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Apri l 2011 | Journal of SEWC 1

April 2011 - Vol: 1 No: 1

Founding Member Organisations 2

SEWC Board Members 2

Editorial Board 2

Guidelines to Authors 2

President's Message 3

Editorial 4

Journa l Sec t ion

Maga zine Sect ion

5 Evolution of Seismic Design Provisions in U.S. Building Codes

Ghosh S.K

10 Precasting: When, Where, How?Gian Carlo Giuliani, Italy

15 Cements and Concrete Mixtures for SustainabilityMehta P. Kumar

23 When Structures MoveKawaguchi, Mamoru

29 Consequences of Ignoring or Mis-Judging the Size Effect in Concrete Design Codes and PracticeBažant, Zdenêk P and Yu

39 Damage Identification of Structures Through Simple and Measurable IndicatorsRaghu Prasad B.K, Lakshmanan N, Gopalakrishnan N and Muthumani K

45 Message from Balaram P, Director, Indian Institute of Science, Bangalore

46 Message from Balakrishnan N, Associate Director, Indian Institute of Science, Bangalore

47 Structural Engineers World Congress - Idea to RealityRoland L Sharpe, Founding President SEWC, Inc.

51 REMINISCENCE - Sankalp - An architectural adventure storyJaisim K, Jaisim Fountainhead, Bangalore

53 Hyderabad International Airport Passenger Terminal Building - Project DescriptionWinston Teng Shu, Principal of Integrated Design Associates Ltd., Hong Kong

55 News

58 Events

Published by: Vidyashankar Hoskere on behalf of SEWC Society, INSTRUCT, 1st Floor, UVCE Alumni Association Building, K.R. Circle,

Banglore - 560 001. Email: [email protected]. Designed and Printed by: 'The Masterbuilder', 102/11, Tripti Apartments,

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Disclaimer: All rights reserved. Reproduction in whole or part without prior written permission prohibited.

The views expressed in this journal are those of the authors and do not reflect those of the publisher.

Content

SEWC

JOURNAL of

Structural Engineers World Congress

International

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Journal of SEWC | Apri l 20112

Foundin g Mem berOrgan isa t ions

Edi t or ia l Board

National Council of StructuralEngineers Associations

NCSEA

International Association of Shell and Spatial Structures

Structural Engineering Instit ute of ASCE American Concrete Institut e

Japan StructuralConsultants Association

Structural Engineers Association of California

SEAOC

SEWCBoard Mem bers

Sundaram R, IndiaPresident- Structural Engineers World

Congress (SEWC) - India

Chairman & Managing Director,

Sundaram Architects Pvt. Ltd

Advisory Board Member - IASSNo. 19, Kumarakrupa Road,

Bangalore 560 001. INDIA

Email : [email protected]

Roland L Sharpe, USAImmediate Past Founding President

Founder President of the Structural

Engineers World Congress ( SEWC)

Consultant with Stanford Linear Accelerator Center,

R. Sharpe Consulting Engineers, 10320

Rolly Road, STE-1, Los Altos Hillf, California, USA


Narendra K Srivastava, CanadaWorking Vice President

Member of International Journal Editorial Boards,

Vice President of the IASS

Adjunct Research Professor at the

University of Waterloo, Canada


Enzo Siviero, ItalyWorking Vice President

Prof.eng, structural consulting engineer in Padova

Teacher Bridge Theory and Design at IUAV

University in Venice

Vice President National University Council Civil

Engineering and Architecture PROGEeST Srl

Via E. degli Scrovegni, 29, 35131 - Padova ItalyEmail : [email protected]

Toshio Okoshi, JapanVice President

Past president of the Japan Structural

Consultants Association, a technical adviser in

Nihon Sekkei and a Professor in Waseda

University. Member of ASCE, IABSE,

JIA, JCI and JSSC


James R. Cagley, P.E.,S.E.Principal, Cagley & Associates,Inc

6141 Executive Blvd, Rockville, MD 20852


A. H-S. Ang, USAResearch Professor, University of California,

Irvine, Email : [email protected]

Sung Pil Chang, South KoreaEmail: [email protected]

Gian Carlo Giuliani, ItalyDr.eng, structural professional enginee

in Milano Italy),

Alberta (Canada) and Cyprus

Advisory Board member IASS, fellow member

ASCE, IABSE, Member ACI. fib, PCI, GLIS


Contributions resulting from original research in the area of structural

Engineering, analysis, design, structural materials and other relatedtopics in the form of technical papers to be published in the

International Journal of Structural Engineers World Congress (SEWC)

are welcome.

Prospective authors are free to prepare the manuscripts in their own

convenient format and submit in MS Word file. The publisher will

modify the format according to the standard format of the journal

before printing.

The authors are requested to particularly not to miss mentioning the

page number of the paper / book in the list of reference.

The manuscript submitted will be peer reviewed and the comment will

be made known to the author.

Guidelines to Authors

Raghu Prasad B.KEditor-in-Chief

Pradeep K.PEditor

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t is my privilege as the President of

SEWC to write in the first journal and

Imagazine of SEWC being released in

Como, Italy. Today Structural engineering

is undergoing a major transformation,

new materials, innovative methods of

construction, different approaches to

design, energy efficient materials and

buildings and the like. So in order to

disseminate knowledge on structural

engineering worldwide we decided to

publish SEWC journal twice a year.

Structural Engineers World Congress wasfirst formed in October 1994. The idea is to

bring all the structural engineers on one

common platform once in four years. The

topics include all design aspects,

practical construction, innovative

solutions, Codes & Practices and design

of energy efficient buildings. Congresses

have been conducted in San Francisco,

USA in 1998, in Yokohama, Japan in 2002 and in

Bangalore, India in 2007. Now in 2011 April it is being held

in COMO, Italy. We are planning 2015 SEWC in

Singapore.

The art of structural designing has become extremely

efficient and interesting since the complexity of the

structural behaviour can be thoroughly analysed with the

available and emerging Software and computers. The

famous adage “form follows function” stands modified to

“form follows structure and function”. This enables

structural designers to adopt interesting and often

amazing configurations for structures such as multi-

storeyed complexes, space frames, shell structures,bridges, long span structures, tall towers and the like.

The congress in Como has a number of Stalwarts

presenting their views on their path breaking works. They

are from different parts of the world and it is going to be

most interesting.

I hope and trust this journal of SEWC will be an useful

addition to the existing Journals.

Sundaram RPresident, Structural Engineers World Congress, WorldwideMember, Advisory Board, IASS

Presi den t 's Messa ge

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t is indeed a privilege to write an

editorial for an inaugural issue. I amIcertain that the entire structural

engineering fraternity would be thrilled to

know that SEWC will hereafter publish

noteworthy contributions in the area of

structural engineering and other related

topics. All these years, SEWC was

content in holding conferences once in 4years. Now, a need is strongly felt among

the structural engineering community

that we need to record our contributions

to the field by publishing the same.

Structural engineering in the world has

grown beyond one's comprehension.

We hear of tall buildings which could be

as tall as almost a km. Similarly we hear

of very long bridges, underpasses/

tunnels. We have witnessed a tunnel

under the sea. We hear of megastructures built in a few months. New

materials have emerged like high

strength, high performance, ultra high

strength, fibre reinforced and light weight

as well as geopolymer concretes. Self

consolidating concrete is a boon to all

structures, especially tall structures

where concrete can be pumped. Such

concretes in the form of liquid when fresh

attaining high strength when cured and set are too good

to believe. They were all dreams three decades ago.

Now is the time to think of energy saving and sustainable

materials like brick and earthen structures like rammed

earth which can withstand even earthquakes. Such

materials also lessen the carbon footprint leading to a

greener planet. New composites using glass and plastics

have emerged recently.

Apart from the new materials mentioned above, research

is still on newer types of forms particularly the spatial and

shell structures. They have been very apt for unusually

long spans. Inflatable structures are finding their presence

in some special applications. Health monitoring and

damage assessment by various techniques and various

types of retrofitting methods are all possible with latest

developments in fracture and damage mechanics.

Especially concrete structures built several decades ago

are in a state of distress due to aggressive environment

and thus there is an urgent need to rehabilitate them by

the methods mentioned above. Some failures in concretestructures which occurred recently are attributed to

another phenomenon called size effect which has opened

up new thoughts on structural design.

Therefore, thus Journal is apt and quite timely as it

addresses many practical issues to be tackled as

mentioned above along with appropriate theories.

I wish the Journal a very bright and long future in the 21st

century.

Edi tor ia l

Prof. Raghu Prasad B.KEditor-in-Chief


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We were able to hold SEWC2011 in Villa Erba

thanks to the local Bodies:

Comune di Como Provincia di Como Camera

di Commercio di Como Villa d'Este

On behalf of the Organising Committee I am

expressing many thanks to the City Mayor and

to the Presidents of the other Bodies for their

valuable and strong support.

Every Congress is organized for improving the

scientific and the technical knowledge of the

participants and of the organizers.All of us, by participating in the Congress, will

benefit of the increasing of our knowledge and

of the sharing of structural engineering

experiences with intercontinental colleagues.

Structural engineering was defined as the art of

using materials, which feature not completely

known behaviors, for resisting not completely

known actions, for designing and building safe

and reliable constructions; a general

improvement for this process is still necessary

and can be achieved during the Congress.

The contributions to SEWC2011 should allow

us to reduce the extents of the unknowns and to

acquire the results of many experiences and

case histories; at the end we will be a little more

confident in our creating effort and will exploit new interesting

structural solutions.

The aims of SEWC2011 are ambitious and I do hope that all of

these will be fulfilled to the participants' satisfaction.

AIM 1 Structural engineers from all the continents will gather and

share their experiencesAIM 2 Being conscious of the existence and the advantages of a

holistic design

AIM 3 Sharing the experience of the cooperation between

Architects and Engineers, taking into account the attitudes

AIM 4 Acquiring the consciousness of the beauty and the

harmony laying in the structural engineering

AIM 5 Finding a clue for special problems - no deep loneliness in

facing unknowns

AIM 6 Discussing scientific clues and case histories for the

design and construction process

AIM 7 Acquiring the development of the characteristics of the

materials

AIM 8 Up dating the knowledge on the structural dynamics

Many other aims could be illustrated but any one of the

participants has his ones.

The aims can be better located in our minds by means of figures

and mainly by works of art which, in my opinion, evocate deeper

thoughts on the matter.

As a conclusion, I do hope that all the delegates will be satisfied

by the whole SEWC2011 event and that will disseminate in their

native Countries the consciousness that structural engineering

has no boundaries.

In addition I wish for all the delegates the warmest greetings from

Italy which they should bring with them in their Countries.

Gian Carlo Giuliani dr. eng.President, SEWC 2011 Organizing Committee

Message from th e Pres ident o f theSEWC 2011 Orga nizing Com m it t ee

Venues of SEWC C. Carrà Hector

and Andromaca

After Le

Corbusier

C. Carrà The

Lover of theEngineer

C. Carrà

Solitude

U.Boccioni -

Unique formsof the spacecontinuum

C. Carrà -

Rhythms andspace continuum

Balla swallows traces and

dynamic sequences

Apri l 2011 | Journal of SEWC

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April 2011 | Journal of SEWC 5

Evolution of Seismic DesignProvisions in U.S. Building Codes

Ghosh, Dr. S.K.

Abstract

Seismic design provisions in building codes of the UnitedStates have undergone profound and far-reachingchanges in recent years. This paper provides an overviewof the major trends that have characterized those

changes. Trends in the broad areas of seismic input, siteclassification and site coefficients, triggers for seismicdetailing requirements, and performance basis of seismicdesign are examined. Future trends are briefly commentedupon.

Seismic Input

The seismic input used in seismic design has changed ina number of significant ways in recent years. Through its1985 edition, the Uniform Building Code (UBC) (1) used aZ-factor that was roughly indicative of the peak accelera-tion on rock corresponding to a 475-year return period

earthquake (an earthquake having a 90% probability ofnon-exceedance in 50 years). There was only an equiva-lent lateral force procedure of seismic design. The upper-bound design base shear or the “flat-top” (or constant-acceleration) part of the design spectrum was soil-inde-pendent; the descending branch or the period-depen-dent (or constant-velocity) part of the design spectrumvaried with 1/T1/2 and was modified by a site coefficient S;there was no lower-bound design base shear.

The Applied Technology Council (ATC) Tentative Provi-sions (2) in 1978 introduced two spectral quantities:

Aa = EPA/g, where EPA was the spectral (pseudo-) accel-eration divided by 2.5 (the division bringing EPA close tothe peak acceleration on rock), and A

v= EPV (in./second)

x 0.4/12 (in./second), where EPV was the spectral (pseudo-) velocity divided by 2.5 (a quantity close to the peak ve-locity on rock). Both quantities corresponded to a 475-year return period earthquake.

The National Earthquake Hazards Reduction ProgramProvisions (NEHRP 1985, NEHRP 1988 and NEHRP 1991(3)) used the same spectral quantities as seismic input.The acceleration-governed part of the design spectrumwas soil-independent, except for a lower plateau for soft

soil sites; the velocity-governed part varied with 1/T2/3 and

was modified by a site coefficient S; there was no lower-bound design base shear.

The Z-factor of the 1988 UBC became indicative of thelarger of two quantities: Aa and Av within a seismic zone.The constant-acceleration part of the design spectrum

remained soil-independent, the lower plateau for soft soilswas eliminated; the constant velocity part now varied with1/T2/3 and was modified by a site coefficient S; a soil-inde-pendent minimum design base shear was added in theequivalent lateral force procedure. All of this remainedunchanged in the 1991 and the 1994 UBC.

The 1994 NEHRP Provisions (3) used soil-modified spec-tral quantities as the ground motion input. A

awas modified

by a short-period site coefficient Fa, yielding C

a; A

vwas

modified by a long-period site coefficient Fv, yielding C

v. Ca

defined the upper-bound design base shear; Cv /T2/3 defined

the descending branch. Thus, the constant-acceleration part

of the design spectrum for the first time became soil-de-pendent. There was still no lower-bound design base shear.

The 1997 UBC was similar to the 1994 NEHRP Provisions,except that a single Z-factor was still used to generate short-period as well as long-period seismic input. C

aof the 1997

UBC was the Z-factor modified by a short-period site coef-ficient, F

a; C

vof the 1997 UBC was the Z-factor modified by

a long-period site coefficient, Fv. C

adefines the flat-top part

of the design spectrum; Cv /T defines the descending branch.

Note the change from 1/T2/3 to 1/T. Two minimum designbase shears are prescribed in the equivalent lateral force

procedure one applicable in all seismic zones, the otherapplicable only in Seismic Zone 4. The higher minimumgoverns when both values are applicable. The minimumvalue that applies in all seismic zones is soil-dependent;the other minimum is soil-independent.

The 1997 and subsequent NEHRP Provisions (3) and theInternational Building Code (IBC) (4) use soil-modified spec-tral accelerations: S

DS= (2/3)F

aS

sand S

D1= (2/3)F

vS

1. S

s

and S1

are spectral accelerations at periods of 0.2 secondand 1.0 second, respectively, corresponding to the maxi-mum considered earthquake on soft rock that is character-istic of the western United States. The maximum consid-

ered earthquake has a 2 percent probability of exceedance

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6 Journal of SEWC | April 2011

Evolution of Seismic Design Provisions in U.S. Building Codes

in 50 years (an approximate return period of 2500 years),except in coastal California where it is the largest earth-quake that can be generated by the known seismicsources.

Two-thirds of the maximum considered earthquake re-places the design (500-year return period) earthquake ofolder codes. S

DSand S

D1define a spectral shape that

changes from location to location, whereas in the past,the same spectral shape was scaled down from areas ofhigh to low seismicity. The flat-top part of the design spec-trum, defined by S

DS,is soil-dependent. The descending

branch of the design spectrum, defined by SD1 /T, is also

soil-dependent. So is the minimum design base shearthat is prescribed for all Seismic Design Categories in theequivalent lateral force procedure (Seismic Design Cat-egory is discussed later), except that in the 2006 IBC, thisminimum has been replaced by a much lower soil-de-pendent minimum value a change that is to be reversed

in the near future. A second minimum base shear is pre-scribed in the equivalent lateral force procedure for build-ings assigned to Seismic Design Categories E and F orfor any building located where S

1= 0.6g. This second

minimum is soil-independent. Designing for two-thirds ofthe maximum considered earthquake provides a uniformlevel of safety against collapse in that earthquake, 2/3being the reciprocal of 1.5, the lower-bound margin ofsafety built into seismic design by U.S. codes (as estab-lished by surveys).

As long as the 500-year return period earthquake was thedesign earthquake, the level of safety against collapse in

the maximum considered earthquake was non-uniformacross the country. This is because in coastal California,the maximum considered earthquake ground motion is onlyabout 1.5 times as strong as the ground motion in a 500-year return period earthquake, whereas in the Midwest andthe East, the maximum considered earthquake groundmotion may be four or five times as strong as the groundmotion in a 500-year return period earthquake.

Site Classification And Site Coefficients

The 1994 NEHRP Provisions3 brought about a major changein site classification and site coefficients used in seismic

design. The new scheme was adopted (with necessarymodifications) into the 1997 UBC and has been adopted(again with necessary modifications) into the 1997 and sub-sequent NEHRP Provisions (3) and the IBC (4). The signifi-cant changes from prior seismic design are as follows:

1. Site Classification - The four Soil Profile Types (S1

through S4) of the 1994 UBC have been replaced by six

Site Classes: A through F. In the 1994 UBC, S1

was rock, S2

was intermediate soil, S3

was soft soil, and S4

was very softsoil.

There are now two categories of rock. Site Class A is hard,

geologically older rock of the eastern United States. Site

Class B is softer, geologically younger rock of the westernUnited States. Site Classes C, D, and E represent progres-sively softer material. Site Class F consists of material sopoor that to be able to design any structure founded on it,a designer must have a site-specific spectrum and mustperform dynamic analysis using that spectrum.

2. Site Coefficients - There used to be one soil factor S;now there are two site coefficients: a short-period oracceleration-related Fa, and a long-period or velocity-dependent Fv.

3. Dependence of Site Coefficients on Seismicity -

Whereas the old S-factor was a function of the Soil ProfileType only (1.0 for S

1, 1.2 for S

2, 1.5 for S

3, and 2.0 for S

4),

each of the new site coefficients (Fa

and Fv), in addition to

being a function of the Site Class, is also dependent on theseismicity at the site. F

a, F

vof the 1994 NEHRP Provisions

are functions of Aa

and Av, respectively. C

a, C

vof the 1997

UBC are both functions of Z. Fa and Fv of the 1997 andsubsequent NEHRP Provisions and the IBC are functionsof S

sand S

1, respectively.

For the same Site Class, the site coefficients Fa

and Fvare

typically larger in areas of low seismicity and smaller in ar-eas of high seismicity. This is directly in line with observa-tions that low-magnitude rock motion is magnified to a largerextent by soft soil deposits than is high-magnitude rockmotion.

4. Maximum Values of Site Coefficients - While the maxi-mum value of the old soil factor S was 2.0 for Type S

4soil,

the maximum values of Fa and Fv are 2.5 and 3.5, respec-tively, in the 1997 and subsequent NEHRP Provisions andthe IBC. This requirement results in significant increases inseismic design forces for buildings (particularly taller build-ings) founded on softer soils in areas of low seismicity.

5. Basis of Site Classification - Soil Profile Types S1

through S4were qualitatively defined in the UBC. The struc-

tural engineer, after reviewing the soils report, typically de-termined the Soil Profile Type. This is to be contrasted withthe new situation where the distinction among the SiteClasses must be based on one of three measured soil prop-erties at the site: the shear wave velocity, the standard pen-

etration resistance (or blow count) or the undrained shearstrength. If one of a number of given conditions is satisfiedat a site, it becomes classified as F. If one of a number ofother given conditions is satisfied at a site, it becomes clas-sified as E. Once Class F and Class E, based on the givenconditions, are ruled out, soil property measurements needto be undertaken.

It is possible for a site to get classified as E, based onproperty measurements as well. The properties need tobe measured over the top 100 ft (30 m) of a site. If the top100 ft (30 m) is not homogeneous, it must be divided intolayers that are reasonably homogeneous, and the proper-

ties of those layers measured. The 1997 NEHRP Provi-

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sions, the 1997 UBC and the 2000 IBC give formulas bywhich to arrive at average soil properties over the top 100ft (30 m), based on those measurements. The IBC, but notthe 1997 UBC or the 1997 NEHRP Provisions, permits thegeotechnical engineer preparing the soils report to esti-mate, rather than measure, the soil properties mentioned

earlier, based on known geologic conditions. In the ab-sence of measured or estimated soil properties, the de-fault Site Class is D, unless the building official has deter-mined that E or F may exist at the site.

Seismic Detailing Requirements

Seismic Zones - In the Uniform Building Code, throughits 1997 edition, and in seismic codes, standards, andother documents based on the UBC, seismic detailingrequirements and other restrictions such as height limitson certain structural systems depended upon the Seis-mic Zone in which a structure was located. Zones wereregions in which the intensity of seismic ground motion,corresponding to a certain probability of occurrence, waswithin certain ranges.

Seismic Performance Categories - Given that publicsafety is a primary code objective, and that not all build-ings in a Seismic Zone are equally crucial to public safety,a new mechanism called the Seismic Performance Cat-egory (SPC) was developed in the ATC 3 document, andwas used in all the NEHRP Provisions through 1994, andin all codes and standards based on the 1994 and earlierNEHRP Provisions (BOCA/NBC 1993, 1996, 1999 (5); SBC1994, 1997, 1999 (6), ASCE 7-93 (7), and ASCE 7-95 (7)).

In all these documents, the SPC, rather than the SeismicZone, was the determinant of seismic detailing require-ments (and other restrictions), thereby dictating that, inmany cases, the seismic design requirements for a hospi-tal be more restrictive than those for a small business struc-ture constructed on the same site. The detailing require-ments for Seismic Performance Categories A & B, C, andD & E were roughly equivalent to those for Seismic Zones0 & 1, 2, and 3 & 4, respectively.

Seismic Design Categories -Seismic Design Categories -Seismic Design Categories -Seismic Design Categories -Seismic Design Categories - The most recent devel-opment has been the establishment of Seismic Design

Categories as the determinant of seismic detailing require-ments in the 1997 and subsequent NEHRP Provisions (3), ASCE 7-98, ASCE 7-02 and ASCE 7-05 (7), and the 2000,2003 and 2006 IBC (4). Recognizing that building perfor-mance during a seismic event depends not only on theseverity of the sub-surface rock motion, but also on thetype of soil upon which a structure is founded, the SDC isa function of location, building occupancy, and soil type.For a structure, the SDC needs to be determined twicefirst as a function of the short-period seismic input param-eter, S

DS, and a second time as a function of the long-

period seismic input parameter, SD1

. The more severe cat-egory governs. The 2003 and 2006 IBC permit the deter-

mination of Seismic Design Category based on short-pe-

riod ground motion alone for short buildings that satisfycertain additional criteria.

Impact of Changes from Seismic Zones to SPCImpact of Changes from Seismic Zones to SPCImpact of Changes from Seismic Zones to SPCImpact of Changes from Seismic Zones to SPCImpact of Changes from Seismic Zones to SPCto SDC -to SDC -to SDC -to SDC -to SDC - Clearly, the procedure for establishing the seis-mic classification of a structure has become more com-plex. Determining the Seismic Zone of a structure simplyrequires establishing the location of the structure on aSeismic Zone map. Determining the Seismic Perfor-mance Category of a structure requires the interpolationof a ground motion parameter on a contour map, basedon the location of the structure, determining the use clas-sification of the structure, and consulting a table. Theprocess leading to the establishment of the SeismicDesign Category of the IBC for a structure involves sev-eral steps, many of which are rather complex.

When ATC 3 in 1978 made the level of detailing (and otherrestrictions concerning permissible structural systems,height, irregularity and analysis procedure) also a functionof occupancy, that was a major departure from prior prac-tice. Now, the level of detailing and other restrictions havebeen made a function of the soil characteristics at the siteof a structure in addition to occupancy. This is a further majordeparture from recent prior practice across the United Statesa move that has important economic implications that havebeen discussed elsewhere (9-11). Earthquake design is nolonger just a regional concern. In unlikely places such as

Atlanta, Georgia, the equivalent of California detailing maybe required, particularly on softer soils.

Performance Basis

Prior to the 1997 NEHRP Provisions - The seismic de-sign provisions of all U.S. codes and similar documentsbased on the 1994 or earlier NEHRP Provisions, or not basedon the NEHRP Provisions, had the following implicit perfor-

mance bases:

(1) For standard-occupancy or ordinary structures, ensurelife safety under the design earthquake, which had a90 percent probability of non-exceedance in 50 yearsor a return period of 475 years.

(2) For assembly buildings or high-occupancy structures,provide enhanced protection of life.

(3) For essential or emergency response facilities, improvecapability to function during and following an earth-quake.

It is generally uneconomical and unnecessary to design astructure to respond elastically to the design earthquake.The design seismic horizontal forces recommended bycodes are generally much less than the elastic responseinertia forces expected to be induced by the design earth-quake. Code-designed structures are expected to ensurelife safety under design earthquake ground shaking becauseof their ability to dissipate seismic energy by inelastic de-

formations in certain localized regions of certain members.

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A decrease in structural stiffness caused by accumulat-ing damage and soil-structure interaction also helps attimes.

The use of seismic design forces prescribed by codesrequires that the critical regions of members have suffi-cient inelastic deformability to enable the structure to sur-vive without collapse when subjected to several cycles ofloading in the inelastic range. This means avoiding allforms of brittle failure and achieving adequate inelasticdeformability by flexural yielding of members. This isachieved through proper detailing of reinforced concretebeams, columns, beam-to-column joints and shear walls,rules for which are presented in the materials chapters ofcodes and in materials standards.

Enhanced protection of life in high-occupancy structureswas provided for in the Uniform Building Code throughthe requirement of an importance factor of 1.5 for the an-chorage of machinery and equipment required for life-

safety systems. The anchorage design forces went up bythis factor. Structural observation, which was required forthis occupancy category, also played a role. An impor-tance factor of 1.25 for the structure itself, an importancefactor of 1.5 for elements of structures, nonstructural com-ponents and elements supported by structures, and struc-tural observation requirements together were used as ameans of improving the capability of essential facilities tofunction during and following an earthquake.

In ATC 3, in the NEHRP Provisions through the 1994 edi-tion, and in codes based on the NEHRP Provisions pre-dating the 1997 edition, enhanced protection of life in

high-occupancy structures (as well as in hazardous andessential facilities) was attempted to be achieved throughthe device of the Seismic Performance Category, whichcombined occupancy with seismic risk at the site of astructure. Higher detailing requirements were prescribedfor higher seismic performance categories. For essentialor emergency response facilities, improved capability tofunction during and following an earthquake was at-tempted to be ensured through stricter limits on interstorydrift.

1997 and Subsequent NEHRP Provisions, ASCE 7-98, ASCE 7-02, and ASCE 7-05, 2000, 2003, and 2006

IBC -

The performance bases of the 1997 NEHRP Provisions, onwhich the seismic design provisions of ASCE 7-98 andsubsequent ASCE 7 standards and the IBC are directlybased, are different from the above. Hamburger (8) hassuggested that the performance bases of the 1997 NEHRPProvisions are as illustrated in Fig. 1, reproduced fromReference 8.

For ordinary structures, life safety under the design earth-quake and collapse prevention under the maximum con-sidered earthquake are ensured by designing the struc-

ture for the effects of code-prescribed seismic forces and

by conforming to the detailing requirements in the ma-terials chapters. Enhanced life safety and collapse pre-vention under the same earthquakes are accomplishedthrough the device of the Seismic Design Category(SDC). It may be noted that essential facilities in so-callednear-fault areas are assigned to SDC F, while other near-

fault structures are assigned to SDC E.The 1997 and subsequent NEHRP Provisions and codesand standards based on them also assign occupancyimportance factors, I, of 1.25 and 1.5 to assembly build-ings and essential facilities, respectively, to partly achievethe higher levels of seismic performance desired for thesestructures. The I-values higher than 1.0 have the effect ofreducing the effective R-values, permitting less inelasticbehavior and, consequently, reduced levels of damage.

From SDC A, B to C to D, detailing requirements increase,and the applicability of certain limited-deformability struc-tural systems becomes restricted. In SDC D, height limitsbegin to apply on certain structural systems, and dynamicanalysis as the basis of design begins to be required forcertain irregular structures.

From SDC D to E to F, detailing requirements do notchange. However, height limits often become more re-strictive and more and more restrictions apply to irregularstructures. Also, structural redundancy must be consid-ered in the design of structures belonging to SDC D, E,and F.

According to Hamburger (8), as shown in Fig. 1, currentU.S. seismic design provisions are supposed to ensure

that ordinary buildings will be immediately occupiablefollowing “frequent earthquakes,” that essential facilitieswill remain operational during and following such earth-quakes, and that assembly buildings will exhibit perfor-mance between the above two. These performance ob-jectives are sought to be met through imposition of limitson the design story drift, ∆, defined as “the difference ofthe deflections of the center of mass on the top and bot-tom of the story under consideration.” Drift limits for high-occupancy buildings are typically more stringent thanthey are for ordinary buildings; for essential facilities, theyare typically more restrictive than those for high-occu-pancy buildings.

The Future

Direct performance-based design, where the design pro-fessional together with the owner or his representativechoose one or more performance objectives (a perfor-mance objective is a desired performance level at a par-ticular ground motion severity or seismic demand), andthose objectives then directly drive the design, is still inthe future of the U.S. codes for new buildings. Such a per-formance-based approach is already available in a stan-dard for existing buildings (ASCE 41-06) (12).

There is little doubt that such direct performance-based

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Fig. 1 Performance Basis of the 1997 NEHRP Provisions


design is the way of the future. Work on performance-baseddesign more sophisticated than what is incorporated inthe ASCE 41 document is currently underway in the UnitedStates under the ATC 58 project being conducted by the

Applied Technology Council. Provisions for direct perfor-mance-based design are likely to replace today's code

provisions where the performance basis is implicit, ratherthan explicit.

Author Affiliation

President, S. K. Ghosh Associates Inc., Palatine, IL, U.S.A.,Email: [email protected]

References

1. International Conference of Building Officials, Uniform Build-ing Code, Whittier, CA, 1991, 1994, 1997.

2. Applied Technology Council, Tentative Provisions for the Devel-opment of Seismic Regulations for Buildings, ATC Publication

ATC 3-06, U.S. Government Printing Office, Washington, DC,1978.

3. Building Seismic Safety Council, NEHRP (National EarthquakeHazards Reduction Program) Recommended Provisions for theDevelopment of Seismic Regulations for New Buildings (andOther Structures), Washington, DC, 1991, 1994, (1997), (2000),(2003).

4. International Code Council, International Building Code, FallsChurch, VA, 2000, 2003, 2006.

5. Building Officials and Code Administrators International, TheBOCA National Building Code, Country Club Hills, IL, 1993,1996, 1999.

6. Southern Building Code Congress International, Standard Build-ing Code, Birmingham, AL, 1994, 1997, 1999.

7. American Society of Civil Engineers, Minimum Design Loads

for Buildings and Other Structures, ASCE 7-93, ASCE 7-95,New York, NY, 1993, 1995, and ASCE 7-98, ASCE 7-02, ASCE7-05, Reston, VA, 2000, 2002, 2005.

8. Hamburger, R.O., “Proposed CRDC Seismic Provisions,” pre-sented to the International Building Code Structural Commit-tee, Orlando, FL, 1997.

9. Ghosh, S.K., “Impact of Earthquake Design Provisions of Inter-national Building Code,” PCI Journal, V. 44, No. 3 (May-June,1999), pp. 90-91.

10. Ghosh, S.K., “New Model Codes and Seismic Design,” Con-crete International, V. 23, No. 7 (July, 2001), American Con-crete Institute, Farmington Hills, MI.

11. Ghosh, S. K., Impact of the Seismic Design Provisions of theInternational Building Code, Structures and Codes Institute,Northbrook, IL, 2001.

12. American Society of Civil Engineers, Seismic Rehabilitation ofExisting Buildings, ASCE 41-06, Reston, VA, 2006.

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Precasting:When, Where, How?

Gian Carlo Giuliani, Italy

Abstract

Conceptual aspects for using the prefabrication and sev-eral applications using liner, planar and spatial elementsfor civil, industrial and tower structures are illustrated inthe article with a mention of the contractor's necessaryskill and equipment.

Keywords

Prefabrication, Concrete, Prestressing, Composite Struc-tures, Buildings, Towers.

When?

Correct structural engineering evolves in a series of stepsstarting with the definition of the purposes and character-istics of the work, continuing with the analysis and theverifications and ending with the preparation of the con-struction drawings and specifications. This process is anextremely valid method that lets face and solve in ad-

vance the problems linked to the different design choices,without having to introduce modifications at a later datethat means forced adaptations and always results in be-ing more expensive.

Precasting is one of the basic choices that needs to bemade at the very beginning of the design process; theconversion of a conventional structure into a precast onevery rarely turns out to be the best choice or completelyfree of compromises.

One needs to decide on precasting straightaway, evalu-ating the pros and cons before adopting it or, on the con-trary, deciding to go for a conventional structure.

However it's always a good idea to also evaluate the alter-native steel solution for the entire structure or for part of it.

When major buildings are dealt with, all aspects of deci-sion about precasting must be carefully considered againat the design stage, because the system and method ofassembly and erection generate temporary actions whichmay require changes of the structural sizing. Not to men-tion the technical/cost effectiveness of such a decision.

The use of precast elements for the load-bearing struc-tures is today commonplace, when applied to floors byusing mass produced girders or panels, and for medium

span industrial buildings, where there's a wide choice of

secondary and primary solutions for roofs and floors andfor the whole framework.

We should, however, point out that the opportunities togain and implement considerable skill and mastery in thefield of concrete constructions are becoming fewer and

fewer and those companies operating in the field ofprecasting are often the safe-keepers of the remainingexperience and the necessary aptitudes.

Where?

The well-known advantages offered by precasting (fac-tory and onsite) for large structures need not be men-tioned here.

It is worth to note that, very often, non conventionalprecasting solutions result in benefits if backed by an ad-equate constructor skill.

In other cases prefabrication is the unique and rationalchoice, which is certainly very challenging for the designbut strongly competitive against the price, the quality andthe delivery time of the conventional construction.

The precasting can be effected in a factory or in the site;the selection among these solutions depends on a num-ber of conditions, like the element size, the transport dis-tance and easiness, the number of similar pieces to bemanufactured and the cost/benefit ratios related with theexistence of factory facilities or with the on site construc-tion of a plant and accounting for a balance of the ele-ment transport cost within the above said locations.

How?

To guarantee the final quality of a project, it is often neces-sary to conceive and design the structure as a precastconstruction right from the very start.

Many types of precasting systems and configurations canbe used, being each one suitable for solving different prob-lems and for complying with the site erection constraints,the element transport conditions, the available equipmentand know how of the construction firm.

The main types of the above said systems can be grouped

in the following categories according to the main dimen-

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sion of the manufactured elements or units: linear, planarand three dimensional; several relevant examples aregiven in the following.

Linear Precasting

Long elements are typically factory produced, in many

cases by using prestressing also, the typical use is forcomponents of frame skeletons.

Verona's Post Office Building

The prefabricated beam and TT floor units for the Verona'sPost Office building (figures 1a,b) are supported by solidcolumns of great height (36 m) and limited cross-section(0.60x0.80 m). Prestressing was applied to the columnsto assure stability during transportation and erection.

Telecom office building in Bologna

In other buildings, precasting has proved to be an excel-

lent idea for just a few elements, such as in the Telecomoffice building in Bologna (figure 2a).

Precast cellular beams span 25 m , bear over the cornertowers and carry the load of 5 or 7 suspended floors(figures 2b,c); the post tensioning cables are shown infigure 2d.

Elevated connections for the new Milano FairExhibition Buildings

In this case 36.50 m span, prefabricated, prestressedbeams were used as floor elements overpassing public

streets; the 20.00 m span main beams are composed of aself supporting steel truss which is integrated with a post-tensioning cable and embedded in concrete in order tokeep the over all structural depth within the limit of 1.45 m(figures 3a, b)

Planar Precasting

Because of their size, two dimensional units are typicallyprefabricated on site.

Prestressed ribbed precast slabs have been successfullyused in several projects to create floors with a great loadcapacity and so avoiding the use of main beams and sec-

ondary elements.The advantages of using slabs come from the structuralbehavior (loads are transferred directly to the columns)and from the monolithic nature of the element. Not tomention the considerably reduced number of production,storage, transportation, erection and in situ assemblingoperations

The disadvantages arise from the need to prepare aprecasting plant on site with forms, reaction beams, anaccelerated curing unit and so on. The need of suitableequipment for handling and erecting large elements, withunit weights greater than those of normal precast ele-

ments, has to be taken into account also.

The costs of setting up the above said equipments arefully compensated by the lower cost of producing similarelements. According to our experience for a total surfacearea to be constructed between 8,000 and 10,000 m2 ,the solution with in site precast planar units becomes acompetitive alternative to precasting and assembling ofseparate elements.

Poli Laboratories building in Rozzano

The prefabricated prestressed ribbed slabs for the fourstory Poli Laboratories building in Rozzano were designedfor a superimposed live load of 12 kN/m2 on a 7.20x8.40 mgrid line pattern, while keeping the floor depth at0.60 m only.

Figures 4a,b show the plates, which were launched onrails at the ground level and lifted to the top of the precastcolumns , and the self stressing form prepared on site.

Roof units for the Milano City Fiera exhibitioncenter

The roof units for the new Milano Fiera City exhibition cen-ter span 20 by 20 meters and are designed for the liveload capacity of 6.0 kN/m2; the whole structure was pre-cast onsite.

Here monolithic plates are being used with single direc-tion ribs and edge beams (figure 5a); the ribs are pre-stressed with bonded strands, while post-tensioningcables are used for the main beams.

Four groups of hydraulic jacks with strand recovery wereused to lift the elements into position.

A self-reacting form (figure 5b) was used and moved onrails to every new position; the form edge panel was tiltedduring this launching to allow passing between the col-umns.

Space Precasting

The theme of space precasting is a complex one becauseof the dimensions of the complete structure and of thecomplicated three dimensional joints which are subjectedto groups of in plane and out of plane actions concen-trated in a reduced area which is located outside the solid

material of the member.In general the structure can be subdivided in sub-ele-ments with linear, planar or space forms to obtain the finalspace configuration; in any case, the design and the con-struction of these members, follow criteria which are dif-ferent from the ones used in the specific above said cat-egories.

In general large span roofs are not easily solved with theuse of the precast elements currently produced. Shellscapable of covering a span of 20 meters are available, butthe main beams for similar distances between the col-umns are too thick and appear unsuitable from the start

due to a high roofing load/own weight ratio.

Precasting: When, Where, How?

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The use of secondary and main floor precast members forlarge spans and the heavy superimposed loads, whichare typical in these building layouts, is impossible also.

New-concepts in the load-bearing system are needed tooptimize the construction system.

Examples of prefabrication of three dimensional structuresare given in the following.

Aeritalia hangar in Turin

For the Aeritalia hangar in Turin, composed of several 30by 30 meters bays, we designed in factory precast thinpre-stressed shells (figure 6a,b) which were fitted with stiff-ening diaphragms at the ends to create the web and theflanges of the main beams.

The shells were aligned on templates at the site and theirdiaphragms were subsequently post stressed in order tocreate the edge main beams.

By using hydraulic jacks, the whole 30 by 30 m unit wasthen lifted up to the top of the columns and suspended tothe capitals by means of stay cables similar to the onesused for bridges (figure 6c); the completed hangar isshown in figure 6d.

Floor units for the Milano City Fiera exhibition center

The first floor of this buildings had to be based on 20 by 20meters bays for the superimposed live load capacity of 15kN/m2 and for housing, inside the depth of the structure,the air intake and exhaust ducts for the ground floor areasas well as piping and wiring for the at level located stands.

An innovative solution was worked out with the concept ofa composite plate featuring concrete top and bottomslabs, connected by means of a shear layer composed ofsteel pipe struts arranged in a 3D truss pattern.

In this structural configuration, the connection betweenthe flanges (conventionally created by webs) has beenreplaced by struts resisting the axial loads created by thethree components of the shear action (figure 7a).

The space between the two slabs can be accessed forinspection and plant maintenance.

The bottom slab is ribbed and prestressed with bondedstrands which cross cast iron nodes embedded in theconcrete and the pin connected to the steel pipes of theshear layer (figure 7b).

The self stressing form was moved on rails to every newbay position (figures 7c,d).

Precast glass fiber reinforced concrete elements placedon the cast iron nodes, located where the pipes convergeclose to the upper surface, constitute the form for castingthe upper slab (figure 7e, f).

All the ducts, pipes and other equipment were positioned

inside the plate (figure 7g)

Four groups of hydraulic jacks lifted the completed plate(weighing a total of 4800 kN, including the already in-stalled ducts) into position (figure 7h); the floor plates laybelow the roof units (figure 7i)

The columns are an integral part of the structural con-cept: pre-cast, with an octagonal cross-section. 25 metershigh and weighing 600 kN; the outer columns are is sight(figure 7k,m).

The support of the composite slab was created by theintroduction of steel-concrete elements in the column withthe necessary recesses to house the bearings, thus allow-ing for lifting the plates without any overhanging elementsand for a reduction of the column bending due to thelocation within the cross-section of the actions transmit-ted by the bearings (figure 7j).

The completed building is shown in figure 7l.

Air traffic control tower at Malaga airport

Because of its location, the control tower at Malaga air-port has a strong visual impact and is composed of three-dimensional shell precast elements for the segments ofthe six wide body ribs which constitute the structure (fig-ure 8g), supports the vertical loads and resist the seismicand the wind actions.

The above said shells were constructed by using the"matching concrete" technology (figure 8a), i.e. castingeach element in a form next to another already cast one,to allow for a "dry" joint erection with a thin layer of epoxy

resin and reinforced by post-tensioned bars (figures 8b,c)

The ramparts for the stairs and the relevant intermediatelandings were precast also.

A service building with an annular shape is located at thebase of the tower and is covered by hypar thin shells whichare supported by X shaped prefabricated elements lo-cated around the outer facade (figures 8c,d,e).

Because of structural reasons related to the limited thick-ness of the shells and to the relevant rise to span ratio, thehypar roof was cast in place.

Air traffic control tower at Barcelona airport

In this case, the use of concrete instead of steel was dic-tated by the client.

The shaft of the Barcelona airport control tower is consti-tuted by prismatic elements with axes lying along straightlines which define a hyperbolic paraboloid; the relevantrectangular sections have a radial orientation.

The challenge of precasting these elements was evenmore demanding, because of the geometry of the shaftdesign featuring helicoid surfaces, and of the necessary

detailing of the connections which were engineered with-


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a) general view of the skeleton(columns, beams, floor units)

b) 36 m long precastprestressed columns

Fig. 1 a, b Verona's Post Office Building

a) general view

b, c) 25 m span cellular beams bearing over the cornertowers and carrying 5 suspended floors

d) postensioning cables for the cellular beams

Fig. 2 a,b,c,d Telecom Office Building in Bologna

a) Prefabricated Prestressed beams b) Main steel truss-concrete beams

Fig.3 Elevated connections for the new Milano Fair ExhibitionBuildings

a) prefab.prestressed slabs b). on site self

stressing form

Fig.4 Poli Laboratories Building in Rozzano

a) 20 by 20m roof units scheme b) self stressing form

Fig. 5 a,b New Milano Fiera City Exhibition Building

out any overhanging parts, (figure 9a,b); because of theinnovative solution the Client required a full scale test (fig-ure 9c), which confirmed the design assumptions.

The erection was performed using the inner self standingaluminum stair structure as a template (figure 9d); thehypar skeleton and the joints got the correct shape (fig-ures 9e,h).

The shaft structure supports the vertical loads, includingthe steel control room (figure 9f,g), and resists the seismicand the wind actions.

The two story building at the base of the tower(figures9i,j,l) is ring shaped and is prefabricated also by usingcolumns, circumference beams, curved facades and sunshading strips cast with a self compacting concrete mixwith white aggregate and cement.

The completed tower is shown in figure 9m.

Conclusions

According to the design and construction experienceearned with the illustrated examples, precast solutionsare very often highly cost effective if the constructor has

the suitable level of expertise required.

In many cases, while it may be far more exacting in termsof engineering, precasting is the only available choicebecause it is far more competitive than on site conven-

tional construction with regard to price, the quality of the

work and construction time.

Author Affiliation

Giuliani, Dr. Eng. Gian Carlo, exclusive Consultant

Redesco srl Milano/Italy [email protected]; Giuliani,Dr. Eng. Mauro Eugenio, exclusive Consultant and GeneralManager Redesco srl Milano/Italy [email protected]


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a) in Factory precast thin pre-stressed shells

c) Whole 30 by 30 unitlifted up

Fig.6 Aeritalia Hangar in Turin

a) Conceptual composition of the multilayer plate

b) Cast iron joint c) Self-stressing form

d) Erection of the forms for theupper slab

e) Ducts placed inside theplate before lifting

a) "Matching Concrete"shells

Fig.7 Floor Units for the milano city fiera Exhibition Center

b) Basement erection

c) Start of shaft erection d) Prefabs and shell

connection

e) Hypar thin shells roofing the basebuilding

Fig.8 Malaga Airport Control Tower:

f) The completedtower

a) Twisted elements d) Erection of theprefabricated

elements usingthe aluminium

stair structure asa template

d) The assembledprefabricated hypar

sk eleton

e) Control roombearing

c) Prefabricatedfacade of thebase building

f) The com-pleted tower

(photo byJ.Azurmendi)

Fig.9 Barcelona Airport Control Tower:


f) The roof and the floor erected g) Column steel elements

j) Column on thefacade

i) The Exhibition building in operation

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Cements and Concrete Mixturesfor Sustainability

Mehta P. Kumar

Abstract

The climate changes, due to man-made global warmingtriggered by steeply rising volume of greenhouse gases,composed mostly of carbon-dioxide, is a very serious is-sue that is being addressed worldwide by every major sec-tor of economy. There is a general acceptance of the viewthat firm measures must be taken without delay to bringdown the global carbon emissions to the 1990 level or lessduring the next 15 years.

The focus of this paper is on portland-cement concrete,which is the most widely used manufactured product in theworld today. Cement production is not only energy-inten-sive but also responsible for direct release of nearly 0.9tonne carbon-dioxide for each tonne of portland clinker,which is the principal component of modern cements. Fif-teen years ago, in 1990, the world production of cementwas slightly more than 1 billion tonnes. In 2005, it alreadycrossed 2 billion tonnes which means that direct CO

2emis-

sions from the portland clinker production have nearlydoubled. Fifteen years from now, with business-as-usual,the estimated cement requirement would be 3.5 biliontonnes, and direct CO

2emissions from cement kilns would

triple the 1990 level. Thus, the challenge before the globalconstruction industry is how to meet the buildings and in-frastructure needs of rapidly growing economies of theworld, and at the same time, cutting down the CO2 emis-sions attributable to cement consumption to the 1990 level,in conformity with other sectors of economy.

Different options for consideration of the construction in-dustry are presented in this paper.

The production and use of blended portland cements con-taining large proportion of complementary cementing ma-terials, such as coal fly ash and granulated blast-furnaceslag provide an excellent strategy for immediate and sub-stantial reduction of direct CO

2emissions associated with

the manufacture of portland-cement clinker. Both EU andNorth American cement standards now permit more than50 % clinker replacement in composite cements. Further-more, the use of composite cements and concrete mixturescontaining large addition of complementary cementingmaterials would yield crack-resisting structural elements ofradically enhanced durability. High-volume fly ash concrete

applications for recently built structures in North America

are cited as typical examples of possible CO2

reduction.

Sustainability - An Introduction

During the 1990s, it became abundantly clear that indus-trialization of the world is happening at an unsustainablespeed. Among the major sustainability issues of publicconcern are high rates of consumption of energy and ma-terials, short service life of manufactured products, and lackof space for safe disposal of huge volumes of solid, liquid,and gaseous wastes generated by human activities. Glo-bal warming, the cumulative effect of these problems, hasemerged today as the most serious sustainability issue ofthe 21st century.

The term, global warming, refers to the greenhouse-gaseffect leading to a steady increase in the earth's surfacetemperature since 1950s. According to a World Watch In-stitute report, twenty-four of the last 27 years have been thewarmest on record. Weather scientists around the world

have concluded that a linear relationship exists betweenthe earth's surface temperature and the atmospheric con-centration of CO

2, which makes up 85 % of the green-

house gases. The current CO2

concentration, about 380ppm (mg/L) in 2005, is the highest in recorded history(Fig. 1). With business as usual, it is projected to increaseat an exponential rate. In 2006, the annual global CO

2

output reached a staggering 30 billion tonnes.

Evidence of global warming is not confined to tempera-ture measurements. The following list includes some ofthe observable effects of the phenomenon:

o A sharp increase in the melting rates of glaciers, polarcaps, and ice sheets.

o Rising ocean levels - a potential threat to coastal popu-lations.

o Unusual increase in frequency and intensity of rain-storms, flash floods, cyclones, hurricanes, heat waves,droughts, and wild fires.

o Adverse impact on current sources of agriculture andwater.

o Disruption of the earth's carbon cycle due to changes in

the botanical species on land and oceans.

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In a series of reports, issued earlier this year by the UnitedNations Intergovernmental Panel on Climate Change, lead-ing weather scientists of the world have unequivocallystated that global warming is occurring, and that it hasbeen triggered by human activities. They have warnedabout devastating consequences of global warming if

immediate action is not taken by national and industryleaders to reduce the carbon dioxide emissions to the1990 level or less.

Although climate change is a global phenomenon, it hasto be tackled in every country individually by each of themajor CO

2emitting sectors of economy, such as power

generation, transportation, and energy consumption as-sociated with the use of buildings, and manufacture ofstructural materials like concrete and steel. According toKyoto Protocol, proposed in 1990 and signed in 2005 by141 countries, the signatories agreed to stabilize the green-house gas emissions by 2012 to 6 % below the 1990 level.

The two largest polluting countries, the U.S. and China,which are responsible for nearly half of the global CO2

emissions, have yet to show a willingness to commit toany specific goals. However, in 2005, many multinationalcorporations, State governments in the U.S., and over 400mayors representing 60 million Americans have signedon to programs that intend to meet or beat the Kyoto tar-gets by 2020. In September 2006, the State of Californiaapproved the Global Warming Solutions Act accordingto which, by 2020, California's CO

2emissions would be

reduced to the 1990 level.

Concrete Industry's Environmental Impact

The subject of environmental impact of the concrete in-dustry is covered by numerous publications across theworld including those listed in References (1-6). The em-bodied energy content, i.e., the sum total of energy re-quired to extract raw materials, manufacture, transport,and install building elements is only 1.3 MJ/kg for 30 MPaconcrete, compared to 9 MJ/kg for recycled steel and 32MJ/kg for new steel. However, being the largest manufac-tured product consumed in the world, quantitatively con-crete represents considerable embodied energy.

Worldwide today, approx. 17,000 million tonnes of con-

crete is being produced annually. Besides natural re-sources, such as aggregates and water, the concrete in-dustry is a large consumer of cement - a manufacturedproduct directly responsible for high CO

2emissions. In

2005, according to Cembureau, the global cement con-sumption was 2,270 million tonnes. Therefore, carbon foot-prints of the global cement industry are very significantconsidering the amount of fossil fuels and electrical powerconsumed for crushing, grinding and transport of materi-als, and for the 1400 to 1500 °C burning operation to makeportland clinker - the principal ingredient of hydrauliccements. The scope of this paper is limited to direct CO

2

emissions, of which approx. 6.3 % of the global emissions

are attributable to portland clinker manufacture.

Co2Emissions From Cement Kilns

Typically, ordinary portland cement is composed of 95 %clinker and 5 % gypsum, which is a complementary ce-menting material (CCM) because it enhances the cementperformance by improving the setting and hardening char-acteristics of the product. Depending on the carbon con-tent of fossil fuels used for clinkering, 0.9 to 1.0 tonnes ofCO

2is directly released from cement kilns during the manu-

facture of clinker. In addition to gypsum, sometimes othermineral additives, commonly known as supplementary ce-menting materials (e.g., coal fly ash, granulated blast-fur-nace slag, natural and calcined pozzolans, pulverized l ime-stone, and silica fume) can either be interground with clin-ker and gypsum or added directly during the concrete mix-ing operation. Large quantities of these materials are avail-able as industrial by-products. As discussed in this paper,when properly used, the mineral additives have the abilityto enhance considerably the workability and durability of

concrete. Therefore, these additives too are treated ascomplementary cementing materials (CCM) in this paper.

Global statistics for 1990 and 2005 on cement produc-tion, CCM consumption, and direct CO

2emission attrib-

utable to portland clinker manufacture, are presented inTable 1. According to the U.S. Geological Survey records,the world consumption of cement in 1990 was 1,044 mil-lion tonnes. From the fragmentary information available itis estimated that, globally, the average clinker factor ofcement (units of clinker per unit of cement) in 1990 was0.9, which means that 940 million tonnes of clinker and104 million tonnes of CCM were used. Assuming the aver-

age CO2 emission rate as 1.0 tonne CO2 /tonne clinker, in1990 the direct CO2

emission from clinker production were940 million tonnes.

In 2005, due to a gradual increase in the use of CCM, it isestimated that 370 million tonnes of CCM were incorpo-rated into 2,270 million tonnes of cement. This gives aclinker factor of 0.84. Also, in 2005, due to increase in theuse of alternate, low-carbon, fuels for burning clinker, theaverage CO

2emission rate dropped to 0.9 tonne per tonne

of clinker. This means that, in 2005, 1,900 million tonnes ofclinker was produced, with 1,700 million tonnes of directCO

2release to the environment. In conclusion, the global

cement industry has almost doubled its annual rate ofdirect CO

2emissions during the last 15 years.

Reducing The Co2Emissions

Comparing the 1990 and 2005 global CO2

emissions di-rectly attributable to clinker production (Table 1), the mag-nitude of the problem becomes at once clear. Not only theannual rate of cement consumption in the world has nearlydoubled during the last 15 years but also, at the currentrate of economic growth in many developing countries, bythe end of the next 15 years the cement requirement is ex-pected to go up to about 3,500 million tonnes a year. As-

suming that during the same period the use of CCM in-

Cements and Concrete Mixtures for Sustainability

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creases from 15 to 20 % of the total cement, the globalclinker production and CO

2emission in 2020 would

amount to 2,800 million tonnes, and 2,520 million tonnes,respectively. To bring down the CO

2emission from 2,520

to 940 million tonnes (the 1990 level) involves nearly atwo-third reduction in clinker requirement, which is un-

likely barring a global catastrophe.In the portland clinker manufacturing process, directrelease of CO

2occurs from two sources, namely the

decomposition of calcium carbonate (the principal rawmaterial) and the combustion of fossil fuels. The formeraccounts for about 0.6 kg CO

2 /kg clinker and the latter

0.25-0.35 kg CO2 /kg clinker (depending on the carbon

content of the fossil fuel); the global average being 0.9 kgCO

2 /kg clinker. Alternate sources of energy other than

fossil fuels are being sought but, at present, they are tooexpensive. Also, there are some cements that do notrequire calcium carbonate as a raw material (e.g.,magnesium phosphate cements) but they are neithereconomical nor technically feasible for large-scaleproduction. Obviously, it will not be possible to achieveany drastic cuts in CO

2emission as long as technical and

economic reasons favor the use of portland clinker as themajor component of hydraulic cements.

The golden rule or mantra for successful resolution of allsustainability issues is, "Consume less, and think more."Based on this mantra, the author proposes the followingthree tools, the simultaneous use of which would enablethe cement industry to reduce greatly the direct CO

2emis-

sion attributable to clinker production:

1. Reduce the consumption of concrete: Architects andstructural designers must develop innovative designsthat minimize the consumption of concrete. Servicelife of repairable structures should be extended as faras possible by the use of proper materials and meth-ods of repair. Low-priority projects should be post-poned or even canceled when possible. Foundations,massive columns and beams of concrete, and pre-cast building components that can be assembled ordis-assembled as needed, should be made with highlydurable concrete mixtures described in this paper.

2. Reduce the cementing materials in concrete mixtures:

Mix design procedures that involve prescriptive codes(e.g., minimum cement content, maximum w/cm, andmuch higher than needed strength) lead toconsiderable waste of cement, besides adverselyaffecting the durability of concrete. Such prescriptivecodes have outlived their usefulness and must bereplaced with performance-based specifications thatpromote durability and sustainability. For example, toachieve durability, it is not the w/c but the cement pastecontent which should be minimized through optimumaggregate grading, use of plasticizing admixtures, andspecifying 56 or 91-day strength for the structuralcomponents that do not have to meet a minimum 28-

day strength requirement.

3. Reduce the clinker factor of cement: Every tonne ofclinker saved would reduce the direct CO

2release from

cement kilns by an equivalent amount. Furthermore, asexplained below, concrete products made with ce-ments of low clinker factor are expected to be muchmore durable when compared to ordinary portland

cement products.Imagine if it were possible to enhance the durability ofmost cement-based products by factor 10 or more, with-out using any expensive technology and materials! Un-questionably, in the long term, this would serve as an ex-cellent strategy for minimizing the wasteful consumptionof cement and other concrete ingredients for general con-struction.

Published literature contains numerous reports showingthat high-early strength concrete mixtures used in mod-ern, high-speed, construction often suffer from lack of du-rability because they are usually made with high content

of a cementing material and a high clinker factor of ce-ment. The hardened product contains a heterogeneouscement paste, with weak interfacial bonding, and is vul-nerable to cracking from excessive thermal shrinkage anddrying shrinkage. According to Reinhardt (7), to minimizethe shrinkage, volume of the paste (cement plus mixingwater) in concrete should not exceed 290 L/m3. High-volume fly ash concrete mixtures, described in this paperare made with cements of low clinker factor (0.4 - 0.5), andless than 290 L/m3 cement paste content. Therefore, theycan be used for making relatively crack-free products ofexcellent durability without any added cost.

What are the Options?

As shown in Table 1, compared to the base year 1990,global carbon emissions direct from portland clinkerproduction have already doubled in the past 15 years. Ifno serious measures are put into place quickly by theworld's construction industry, i.e. with business-as-usual itis estimated that the rate of direct carbon emissions fromcement kilns will almost triple in the next 15 years (Table 2,Option 1). Table 2 also includes data on two other options,an easy option (Option 2) and a challenging but preferableoption (Option 3). Note that Option 1 (business-as-usual)data will be used as a reference point for both Options 2

and 3, that are discussed next.

According to Option 2, by 2020, if the global concreteconstruction industry is able to reduce the concreteconsumption by 20% (compared to Option 1) and at thesame time increase the CCM utilization to 30% of the totalcement, these steps will have the effect of reducing thedirect CO

2emissions from cement kilns to 1,760 million

tonnes. This is nearly twice as much as the 1990 emissionsrate of 940 million tonnes.

According to Option 3, in 2020, the total cementing mate-rial (2,100 tonnes) would comprise 1050 million tonnes of

portland clinker and the same amount of complementary


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cementing materials. In Table 3, estimates of differenttypes and amounts of complementary cementing materi-als that would be available for use in 2020 are given. Notethat coal fly ash is expected to make up 760 million tonnesor nearly three-fourths of the total CCM. Would such alarge quantity of fly ash be available in 2020? It is difficult

to provide a definite answer, but let us examine the as-sumptions under which this is possible.

In the foreseeable future, fossil fuels will continue to remainthe primary source of power generation, and due to thelow cost of coal, expansion of the coal-fired power industrywill continue in major coal-producing countries such asChina, India, and the United States. According to oneestimate, approximately 1200 million tonnes of fly ashwould be available in 2020. It would indeed be aformidable job to ensure that nearly two-thirds of the flyash produced by coal-fired power plants is suitable foruse as a complementary cementing material. This goal

can be accomplished, provided the key players, i.e., theproducers of fly ash, the consumers of cement andconcrete, and individuals or organizations responsible forspecifications work together to overcome the problems,discussed below.

The power sector of the global economy is the largestsingle source of carbon emissions in the world. It is esti-mated that about 7 billion tonnes a year of CO

2is being

released today from the combustion of all fossil fuels, andthat the coal-fired power plants alone generate 2 billiontonnes of CO

2. Besides carbon emissions, according to

Malhotra (5), coal combustion in 2005 generated approxi-

mately 900 million tonnes of solid by-products including600 million tonnes of fly ash. Due to rapidly changingrates of fly ash production and use in the two large econo-mies of the world, China and India, which meet three-quar-ters of their electrical power requirement from coal-firedfurnaces, accurate data on today's global rates of fly ashproduction and utilization are not available. However, arough estimate shows that the current rate of fly ash pro-duction is approximately 750 million tonnes/year, and thatnearly 140 million tonnes/year is being consumed as aningredient of blended cements and concrete mixtures.The remaining fly ash either ends up in low-value applica-tions, such as road sub-bases and embankments, or is

disposed to landfills and ponds.

When used as a complementary cementing material, eachtonne of fly ash can replace a tonne of portland clinker.Diverting fly ash from the waste stream and using it toreduce direct carbon emissions from the cement industryis like killing two birds with one stone. Therefore, increasingthe utilization of most of the available fly ash as a comple-mentary cementing material is, unquestionably, the mostpowerful tool for reducing the environmental impact oftwo major sectors of our industrial economy, namely thecement industry and the coal-fired power industry.

In spite of proven technical, economic, and ecological

benefits from the incorporation of high volumes of fly ashin cements and concrete mixtures, why does the fly ashutilization rate as a complementary cementing materialremain so low? Obsolete prescriptive codes, lack of state-of-the-art information to architects and structural design-ers, and lax quality control in power plants are amongsome of the reasons. Also, all of the currently produced flyash is not suitable for use as a complementary cementingmaterial, however cost-effective methods are available tobeneficiate the material that does not to meet the mini-mum fineness and maximum carbon content require-ments - the two important parameters by which the fly ashsuitability is judged by the cement and concrete indus-tries (5).

Sustainable Cements

Sustainable, portland-clinker based cements can bemade with 0.5 or even lower clinker factor using a highvolume of granulated blast furnace slag (gbfs), or coal fly

ash (ASTM Class F or C), or a combination of both. Natu-ral or calcined pozzolans, in combination with fly ash and/ or gbfs, may also be used. Compared to portland ce-ment, the high-volume fly ash and slag cements are some-what slower in setting and hardening, but they are moresuitable for producing highly durable concrete products.Unfortunately, worldwide, the conventional concrete con-struction practice is dominated by prescriptive specifica-tions that do not permit the use of high volume of mineraladditives.

Cements containing a high-volume of complementary ce-menting materials can now be manufactured in accor-

dance with ASTM C 1157 - a new standard specificationfor hydraulic cements, which is performance-based. How-ever, in North America significant amount of blended port-land cements are not produced, because it is customaryto add mineral admixtures at the ready-mixed concreteplants. According to American Coal Ash Association, atpresent about 14 million of the available 70 million tonnes/ year fly ash is being used as a complementary cementingmaterial in concrete mixtures. Reliable estimates are notavailable from China and India, however, it is reportedthat significant quantities of blended cements containing20-30 % fly ash, are being manufactured in these countries.

The European Cement Specification EN 197/1, issued in2002, contains 26 types of blended portland cements in-cluding three cement types that have clinker factors rang-ing between 0.35 and 0.64. Type III-A Cement covers slagcements with 36-65 % gbfs; Type IV-B Cement covers poz-zolan cements with 36-55 % pozzolans including fly ash,natural or calcined pozzolanic minerals, and silica fume;Type V-A Cement covers composite cements containing18-30 % gbfs plus 18-30 % pozzolans. According toCembureau statistics for 2005, the consumption of ordi-nary portland cement in the European Union countrieshas dropped to 30 % of the total cement produced,whereas blended portland cements containing up to 25

% CCM have captured 57 % of the market share, and


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blended cements with more than 25 % CCM are approach-ing 10 % of the total cement consumption.

Sustainable Concrete Mixtures

For reducing direct carbon emissions attributable to port-land clinker production, the emerging technology of high-

volume fly ash (HVFA) concrete is an excellent exampleshowing how highly durable and sustainable concrete mix-tures, with clinker factor of 0.5 or less, can be produced byusing ordinary coal fly ash (ASTM Class F or Class C),which are available in most parts of the world in largeamounts. The composition and characteristics of HVFAconcrete are discussed in many publications and arebriefly described below. Note that concrete mixtures withsimilar properties can be produced by using a high vol-ume of granulated blast-furnace slag or a combination offly ash and slag, with or without other mineral admixtures.

The cementing material in HVFA concrete is composed of

ordinary portland cement together with at least 50 % fly ashby mass of the total cementing material. The mix has a lowwater content (100-130 kg/m3), and a low content of ce-menting materials (e.g. 300 kg/m3 for ordinary strength andmax. 400 kg/m3 for high-strength). The plasticizing actionof the high volume of fly ash imparts excellent workabilityeven at w/cem of the order of 0.4. However, chemical plas-ticizers are often used, when lower w/cem are required.Occasionally, an air-entraining admixture is also includedin the mix when protection against frost action is sought.

Compared to portland-cement concrete, the HVFA con-crete mixtures designed to achieve the same 28-d

strength exhibit superior workability without segregatingeven at slump values of 200-250 mm. Typically, the con-crete is slow in setting and hardening, i.e. develop slightlylower strength at 3 and 7-d, similar strength at 28-d, andmuch higher strength at 90-d and 1-year. The pozzolanicreaction leading to complete removal of calcium hydrox-ide from cement hydration products enables the HVFAconcrete to become highly resistant to alkali-aggregatereaction, sulfate and other chemical attacks, and reinforce-ment corrosion (due to very low electric conductivity). Fur-thermore, the HVFA concrete mixtures are much less vul-nerable to cracking from both the thermal shrinkage (less

heat of hydration), and the drying shrinkage (less volumeof cement paste). Therefore, in addition to very low clinkerfactor, the ability of HVFA concrete to enhance the dura-bility by factor 5 to10 makes it a highly suitable materialfor construction of sustainable structures in the future. Theauthor has been involved with many field applications ofHVFA concrete that are described in earlier publications(8-11). Three recently built structures in the U.S., withlarge reduction in CO

2-emissions resulting from the use of

HVFA concrete, are described below.

A Hindu Temple, built with concrete members designedto endure for 1,000 years or more, was constructed in Chi-

cago in 2003 (Fig. 2). The superstructure of the temple is

composed of some 40,000 individual segments of intri-cately carved white marble (Fig. 2). Unreinforced mono-lith slabs are a part of the foundation, supported by 250drilled piers, 9 m high and 1 m diameter. All structuralelements were made with, cast-in-place, HVFA concretecontaining 105 kg/m3 ASTM Type I portland cement and195 kg/m3 Class C fly ash, 2 L/m3 polycarboxylatesuperplasticizer, and 100 kg/m3 water. Note that the totalcementing material was 300 kg/m3, the clinker factor wasonly 0.33, and the w/cem was also 0.33. The fresh mix had150-200 mm slump and showed excellent pumpability,which made it possible to place and finish 400 m3 con-crete for the main prayer-hall slab (22 by 18 by 1 m), in lessthan 5 hours. Typical compressive strength values at 3-d,7-d, 56-d, and 1-y were 10 MPa, 27 MPa, 48 MPa, and 60MPa, respectively. No structural cracks in any concretemember were reported. Also, the chloride penetrationpermeability, which is an excellent index of long term du-rability of concrete, was surprisingly low (< 200 coulombs)in 1-year old core samples. A conventional concrete mixwould have required 400 kg/m3 portland cement toachieve similar high-strength. The use of 3,000 m3 HVFAconcrete mix resulted in 900 tonnes of portland cementsaving, which corresponds to about 800 tonnes of CO

2

emissions reduction.

The Utah State Capitol Building, Salt Lake City, under-went seismic rehabilitation in 2006 (Fig. 3a). Due to heavilycongested reinforcement in the foundations, floor beams,and shear walls, a nearly self-consolidating mix contain-ing 160 kg/m3 ordinary portland cement, 200 kg/m3 ASTMClass F fly ash, 138 kg/m3 water, and 1 L/m3

superplasticizer was used. The clinker factor of this mix

was 0.44, and the w/cem was 0.38. The specified slumpand 28-d compressive strength were 150 mm and 27 MPa,respectively. The field concrete showed an average of225 mm slump and 34 MPa strength. It is estimated thatthis 4,500 m3 HVFA concrete job, enabled 900 tonnes ofreduction in CO

2emissions attributable to clinker saving.

The CITRIS Building at the University of California at Ber-keley contains 10,700 m3 HVFA concrete - the largest vol-ume ever used for construction of a single building. Forfoundations and mats, a concrete mix containing 160 kg/ m3 of ASTM Type II portland cement, 160 kg of Class F flyash, and 123 kg/m3 water (0.37 w/cem) was used. For

heavily reinforced columns, walls, beams, girders andslabs, a concrete mix containing 200 kg/m3 ASTM Type IIportland cement, 200 kg/m3 Class F fly ash, and 140 kg/ m3 water (0.35 w/cem) was used. In both cases the clinkerfactor is 0.50. The specified compressive strength was 27MPa @ 28-d for all structural members except the foun-dations and mats which were designed for a specifiedstrength of minimum 27 MPa @ 56-d. Note that the con-crete used for reinforced columns achieved 20 MPastrength @ 7-d, and nearly 40 MPa @ 56-d. It is estimatedthat the choice of HVFA concrete as a structural materialfor the CITRIS Building resulted in a reduction of 1950tonnes of direct CO

2emissions attributable to the low clin-

ker factor of the cementing material.


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Economic and Technical Barriers

For utilization of high proportions of complementary ce-menting materials in general construction, human per-ception appears to be a far more formidable barrier thanactual economic and technical barrier. According toMeryman and Silman (12):

Sometimes, there is a perception that a "green" materialor practice is more costly, but on further examination, itproves no to be so; often it is just a matter of getting on theother side of the learning curve. We must clarify the differ-ence between life cycle cost and first cost, since manysustainable products have better life cycle performance.We need to define the term 'economic' and include thecollateral cost of using non-sustainable practices.

The use of sustainable cements and concrete mixtures,described in this paper, would undoubtedly produce struc-tural members of high durability. However, a statistical

life-cycle analysis is not possible because there are noreliable laboratory tests for quantitative assessment oflong-term durability of field structures. Other major barri-ers are lack of codes of recommended practice and un-willingness of structural designers and engineers to beamong the first to champion the use of new materials.

Again, according to Meryman and Silman (12):

How can an underused material or method become tried,trusted and ultimately the standard? These materials andmethods need advocates. As technical professionals,structural engineers can use specifications to communi-cate a commitment to and confidence in more sustain-

able choices. By taking responsibility for those practices,we become their advocates.

From my own personal experience, I confirm the observa-tions of Meryman and Silman. I have come to the conclu-sion that it is the hand that writes the specifications whichholds the power of leading the concrete construction in-dustry to an era of sustainability. Codes of recommendedpractice advocated by organizations, such as AmericanConcrete Institute and U.S. Green Building Council, canplay an important part in accelerating the sustainability ofthe concrete industry. For instance, the USGBC point-rating system for new construction has already become a

powerful driving force for sustainable building designs.The rating system awards sufficient points for buildingsthat would consume less energy in their use. A similaremphasis is needed in favor of sustainable materials thatproduce less CO

2during their manufacture. By suitably

amending the rating system so that some points basedon CO

2emissions reduction are directly assigned for the

use of sustainable materials in new construction, theUSGBC can help sustainability of the cement and con-crete industries.

Concluding Remarks

The high carbon dioxide emission rate of today's industri-

alized society has triggered climate change that is po-tentially devastating to life on the planet earth. To meetthe global concrete demand, which was 17 billion tonnesin 2005, two billion tonnes of CO

2were directly released to

the atmosphere from the manufacturing process of port-land-cement clinker, which is the major component of

modern hydraulic cements. With business-as-usual, thedirect CO2

emissions from portland clinker production, inthe year 2020, would triple the 1990 level unless immedi-ate steps are taken to bring down the emissions by mak-ing significant reductions in the: (a) global concrete con-sumption, (b) volume of cement paste in concrete, and(c) proportion of portland clinker in cement.

Examples of recently built structures prove that by usinghigh volume of coal fly ash and other industrial wastes ascomplementary cementing materials with portland clin-ker, we can produce low cost, highly durable, and sustain-able cements and concrete mixtures that would signifi-

cantly reduce both the carbon footprints of the cementindustry and the environmental impact of the coal-firedpower generation industry.

It seems that the game of unrestricted growth, in a finiteplanet, by reckless use of energy and materials, is over.Most sectors of the global economy have already initi-ated action plans to bring down their share of carbonemission to the 1990 level or less, by the year 2020. Theconstruction industry is already pursuing the goal of de-signing and constructing sustainable buildings that con-sume less energy and resources to maintain. Now, allsegments of the construction industry - owners, design-

ers, contractors, and cement and concrete manufactur-ers - will have to join the new game of building sustainablestructures using only sustainable materials.

We have the tools to win this game. What is needed now isthe will and the individual initiative. To paraphrase JohnF. Kennedy, "Ask not what others can do. Ask what youcan do to promote the use of sustainable constructionmaterials."

Acknowledgement

The author would like to thank Mason Walters of ForellElsesser Engineers, San Francisco, for the photographs

in Figs. 3 and 4.

Author Affiliation

Mehta Prof. P. Kumar <[email protected]> Univer-sity of California, Berkeley, U.S.A.

References

1. P.K. Mehta, and P.J.M. Monteiro, "Concrete: Microstructure, Prop-erties, and Materials", McGraw-Hill, New York, 2006

2. ACI Board Advisory Committee on Sustainable Development,"White Paper on Sustainable Development", Concrete Interna-

tional, American Concrete Institute, Vol. 27 No. 2, 2005, pp. 19-21


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*Estimated amounts of CCM used in 1990 and 2005 are 10 % and15 % of total cementing material, respectively.

Table 1 Global Direct CO2 Emission from Cement Kilns (MillionTonnes)

Table 2 Estimates of Global Cement Consumption in 2020,and Direct CO2 Emissions from Cement Kilns (Million Tonnes)

Table 3 Estimated Consumption of Complementary Cement-

ing Materials (Million Tonnes)

3. The Concrete Center of U.K., "Sustainable Concrete",

www.concretecenter.com, 2007, 18 pages

4. World Business Council for Sustainable Development, "The Ce-ment Sustainability Initiative", www.wbcsdcement.org, Geneva,Switzerland, 2007

5. V.M. Malhotra, "Reducing CO2 Emissions", Concrete Interna-tional, American Concrete Institute, Vol. 28 No. 9, 2006, pp.42-45

6. P.K. Mehta, "Greening of the Concrete Industry for SustainableDevelopment", ibid., Vol. 24 No. 7, 2002, pp. 23-28

7. H.W. Reinhardt, "New German Guideline for Design ofConcrete Structures for Containment of Hazardous Materials",Otto Graf Journal, FMPA, Univ. of Stuttgard, Germany, Vol. 17,2006, pp. 9-17

8. P.K. Mehta and W.S. Langley, "Monolith Foundation Built to Last

a 1,000 Years", Concrete International, American Concrete Insti-

tute, Vol. 22 No. 7, July 2000, pp. 27-32

9. D. Manmohan and P.K. Mehta, "Heavily Reinforced Shear Walls

and Reinforced Foundations Built with Green Concrete", ibid.,

Vol. 24 No. 8, 2002, pp. 64-70

10. P.K. Mehta and D. Manmohan, "Sustainable, High-Performance

Concrete Structures", ibid., Vol. 28 No. 7, 2006, pp. 37-42

11. V.M. Malhotra and P.K. Mehta, "High-Performance, High-Vol-

ume Fly Ash Concrete", Supplementary Cementing Materials

for Sustainable Development, Ottawa, Canada, 2002

12. H. Meryman and R. Silman, "Sustainable Engineering - UsingSpecifications to Make it Happen", Structural Engineering In-ternational, Vol. 14 No. 3, Aug. 2004, pp 216-219

Fig. 1 Historical and Future Atmospheric CO2, Based onIPCC Reports (1)

Business-as-usual scenario

Fig. 2 The BAPS Hindu Temple, Chicago, 2004High-Volume Fly Ash was Used for

Unreinforced Monolith Foundations and Drilled Piers


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Fig. 3a Utah State Capitol Building After SeismicRehabilitation, 2006

High-Volume Fly Ash was Used for Reinforced Foundations,Beams, and Shear Walls

Fig. 3b Utah State Capitol Building After SeismicRehabilitation, 2006

Excellent Pumpability and Workability of Nearly Self-consolidating Concrete Mixture

Fig. 4a CITRIS Bldg., Univ. of California, 2007Mat Foundation Under Construction

Fig. 4b CITRIS Bldg., Univ. of California, 2007Heavily Reinforced Columns Under Construction


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When Structures MoveKawaguchi, Prof. Mamoru

Abstract

In the present paper moving aspects of structures aretaken up. In our daily structural design the structures areassumed to be immovable, and most of structural calcu-lations are carried out on the basis of static principles.

Although we know that a structure always produces sucha movement due to loading that is referred to as deforma-tion or displacement, its magnitude is normally too smallto be significant in comparison with the dimensions of the

structure, and its effect on the structural behaviors is ne-glected, the whole phenomenon being treated as static.There are cases, however, where large movements areactually experienced by our structures due to differentreasons. Many of them are due to excessive loading andunexpected instability, often leading to collapse of thestructures. Some other cases are related to vibration whereresonance of structures with external agencies such asearthquakes and wind is a key question. Self-excited os-cillation sometimes produces catastrophic and very spec-tacular motion of structures. Controlled motions can beobtained by adopting isolators to cope with the effects ofearthquakes. Dampers which are often incorporated in

seismic isolation systems are normally rather still, butmotion of tuned mass dampers is sometimes very signifi-cant. Structures can be designed to be assembled on theground and then hoisted to the position. In erection ofsuch structures a big movement is observed as inPantadome System. Finally those structures which areoriginally intended to move are described with examplesof rocking stones and a flying carp.

Keywords: moving structures, collapse, excessive defor-mation, controlled motion, earthquake isolation, self-ex-cited oscillation, Pantadome system, tuned-mass damp-ers, pendulum system

Undesirable Movements

There are unfavorable movements which poor structureshave to experience under some undesirable conditions.They are movements due to excessive snow loads, earth-quakes, wind, structural deterioration and so on, and thosemovements have different characteristics due to the na-tures of the causes.

Collapsing Movements due to Snow Loads

Structures standing on the principle of arches and domesare sometimes in danger of yielding collapsing move-ments due to unstable deformation of the compressive

members.

One of such examples is the dome for a trade center inBucharest which collapsed in January 1963 (Fig.ures.1and 2). The dome had a spherical shape to cover a plan of93.5m in diameter. The dome experienced a huge "snap-through" deformation, or a deformation from convex toconcave geometries under the snow load of 2,000 kN whichwas less than 30% of the design snow load.

Another example of this kind is a collapse of the hangingroof of "Palasport" in Milan which occurred in January 1985

(Figures 3 and 4). It had a circular plan of 128m in diam-eter. The presumed snow load on the roof at the time ofcollapse was 1.4 kN/m2 while the standard snow loadwas 0.9kN/m2 . The roof of this velodrome was a saddle-shaped hanging roof that should have more sufficientpotential strength, but the collapse was caused by thebuckling of the ring beam the section of which had been abox section of thin steel plates.

In the above examples the structures must have experi-enced very large movements during the collapse, but nosuch movements were visually recorded. There are manyother examples of structural collapse due to snow loads,but observation records of the collapsing movements arescarce. In general the visual records of collapsing move-ments of large-span roofs due to snow are difficult to make,since firstly it is not easy to anticipate the time of collapsewhich often occurs at a lower loading level than in design,and secondly weather and shooting condition are badbecause of snow falling and snow drift.

Destructive Movements due to Earthquakes

Earthquakes make structures produce significant move-ments which are often destructive. Different from the ef-fects of snow, earthquakes are not loading on the struc-tures but vibrational motion of the grounds on which the

structures stand. Therefore the motion induced in the struc-tures by earthquakes is closely related to the vibrationalcharacteristics of the structures, and when the naturalperiods of the structure are close to those of the prevailingground motion, the motion of the structures can be de-structive. On the other hand this type of motion can oftenbe controlled by means of vibration technology. The idealcase of such a control is seismic isolation, as will be de-scribed later.There have been so many destructive mo-tions of structures due to earthquakes, and some of themhave been recorded numerically in the form of accelera-tion data, but visual records of such motions are againvery scarce because of the facts that prediction of de-

structive earthquakes is again very difficult and that pho-

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tographers are also in danger of their lives during the se-vere earthquakes.

Uncontrolled Movements due to Wind

In design of comparatively rigid structures we treat theeffects of wind as static loads. When a structure is soft,

however, we have to take into account dynamic effect ofwind, and motions of the structure due to this effect.Dynamic effect of wind due to disturbance in the windflow itself is sometimes referred to as buffeting or gustyeffect, and resonance of the structure with this effect isoften discussed.

Another and more important effect of wind is vortex-in-duced vibration, and still more important is self-excitedoscillation or flutter starting from the vortex-induced vi-bration. In such a motion the structure takes in energyfrom constant air flow around it to grow the motion until itbecomes catastrophic. The collapse of Tacoma Narrows

Bridge is explained as the result of such phenomena (Fig-ures. 5 and 6). In general the magnitude as well as themode of self-excited motion is very big and exceeds ourimagination, often being even spectacular. Such motionsare comparatively easy to record visually, since the timeof strong wind can be predicted, the motion of this kindlasts for relatively long time and the photographer is notalways in a dangerous situation.

Controlled Movements

Seismic Isolation

Seismic isolation is a technology to control the response

of structures due to earthquake ground motion. The isola-tion technology is normally applied in combination withenergy-absorbing damping systems. The most popularseismic isolation system is the laminated rubber shoesthat support the structures. However, there are other iso-lation systems effective to control seismic motions in morerational manners than laminated rubber system, whichwill be described in this section.

Pendulum Isolators

A pendulum system is one of the basic methods of seis-mic isolation, having the same fundamental principle in

common with seismographs. As shown in Figure 7, pen-dulums used in engineering include (a) simple pendu-lum, (b) physical pendulum, and

(c) translational pendulum.

It is well known that the natural period T of a simple pen-dulum is given as follows with the

length of the hanger L, and the gravitationalacceleration g.

(1)

One advantage of a pendulum seismic isolator is that thelength of the hanger L is the only parameter governing itsnatural period, and the mass of the object to be isolatedexerts no effect on it at all. Thus, desired periods can beobtained by simply changing the hanger length. This is thegreatest advantage of pendulum seismic isolators com-

pared to laminated rubber seismic isolators in which thenatural period is determined by the mass and rigidity ofisolation structure.

The natural period is slightly elongated if the amplitude ismade larger. The elongation, however, is minute. Thus, theabove equation (1) can be considered valid for all practicalcases. This is another advantage of the pendulum seismicisolator compared to the laminated rubber system, of whichthe deformability is limited. Wide selection of materials isavailable for the hanger. For example, technology for fire-proofing has already reached a mature state if steel is to beused. As discussed above, seismic isolators using pendu-

lum principle possess considerable merit.Considering that seismic isolators must also function as apart of structural support, simple pendulum shown in (a) ofFigure7 is obviously difficult to use. Natural period of physi-cal pendulum shown in (b), on the other hand, fluctuatesalong with the location of center of mass as well as themoment of inertia of the system. Thus, translational pendu-lum shown in (c), whose natural period is only affected bythe hanger length as in the simple pendulum, would beappropriate for use as a seismic isolation device.

One possible application of the translational pendulum seis-mic isolator is for individual floors. A floor suspended froma girder of a building frame as shown in Figure 8 wasadopted for the exhibition rooms of an actual museum forpottery and porcelain wares (in Gifu Prefecture, Japan, com-pleted in 2001). The area of the suspended floor is about1,000 m2, and its mass is about 1,000 tons. Hinges havinguniversal joints are used for the upper and lower ends ofthe hanger. If the hanger is made to be 4.5 m long, Equa-tion (1) yields a natural period of more than 4 seconds, whichis considered sufficiently long for seismic isolation. A se-ries of seismic isolation tests showed that the system waseffective to minimize the seismic effects on the floor.

Rocking Pendulum Isolators

A paddle isolator is based on a rocking pendulum prin-ciple, the concept of which has a long history. The firstexample of isolated foundations in Japan was designedby Ryuichi Oka in 1932, as a column having a sphericalend at the bottom and connected to the superstructurevia a spherical hinge at the top. Due to rocking motion ofthe column, the superstructure moves in a trochoidal curve.

This concept, however, was impractical as production ofspherical elements required considerable skill and man-hours, and column design sometimes interfered with overallarchitectural planning. In the present design rocking mo-

tion of the sphere was resolved into the orthogonal com-

When Structures Move

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ponents along the X- and Y-axes on a plane coordinate.Then, a mechanism was designed which assigns the com-ponents of the rocking motion in the directions of X- and Y-axes to the upper and lower ends of a column. Paddle iso-lator was named after a kayak paddle, as the form of thepresent column resembles it. As shown in Figure 9, a paddle

isolator consists of a column provided with "blades" on thetop and bottom ends whose curvatures are designed to beorthogonal to each other. This column allows resolution ofany horizontal motion in an arbitrary direction into two di-rections, and the isolated part of the building is free to movein the horizontal direction. Referring to Figure 10, the natu-ral period of a rocking pendulum is determined by the lengthof the isolation column L and the radius of curvature of ablade R, and can be obtained by Equation (2).

(2)

One of the features of the rocking pendulum isolator is thatits natural period is not governed by the mass of structureto be supported or any mechanical properties of the mate-rials used in the isolator, similar to the translational pendu-lum isolator. On the other hand, the paddle isolation col-umn may be designed with any length, unlike the transla-tional pendulum isolator. As such, isolating layer may ei-ther be placed just underneath the foundation, or the entireground floor may be designed as an isolating layer.

This enables design of seismic isolators having longer pe-riods, which were conventionally deemed impossible.

In order to confirm the effect of the paddle isolators, acrylicspecimens (shown in Figure 12, the floor panel being 40cm by 40 cm) were manufactured and tested. The test re-sults indicated fairly constant natural periods for paddle iso-lators, regardless of the amplitude of the given motion orthe mass of superstructure. Furthermore, the torsion move-ment was hardly observed even when the mass supportedby the isolation layer was largely shifted off the center. Fig-ure 11 shows the rates of the observed acceleration re-sponses when the seismic motion based on the records ofthe actual earthquakes were applied to the vibration table.

As shown, response in the upper part of the isolating layer

was reduced sufficiently. It was also confirmed that the ef-fect is not influenced by the direction of input seismic mo-tion.

Damping Systems

Damping systems are often used in combination with seis-mic isolators, but they are of course used by themselvesas well for the purpose of energy absorption. Most com-monly used in vibration control are viscous, frictional, hys-teretic and tuned-mass dampers. The first three of theabove dampers control the vibrational motion of the struc-tures by dissipating the energy in the form of heat, while

the tuned-mass dampers transform the energy of their

mother systems into the motion of themselves. So the ef-fect of tuned-mass dampers can be visually confirmed bymeans of scaled model tests, where the transfer of motionfrom the structure to the dampers is clearly observed.

Human-Induced Vibration

Soft footbridges often produce significant vibrational mo-tion that is induced by the movement of pedestrians cross-ing the bridges. It is interesting to note that when the move-ment of the bridge, especially the transverse horizontal com-ponent of which is big enough to be felt by the pedestrians,they are apt to try to secure themselves by tuning their stepsto the period of the motion of the bridge, resulting in ampli-fication of the bridge motion. Vibration of Millennium Bridgein London was a typical example, which was solved by in-

corporating a passive damping system in the bridge.

Designed Movements

Pantadome System

Structures are sometimes designed to move during con-struction for safe, efficient and economical erection. A pat-ented structural system called 'Pantadome System' wasdeveloped by the author with such an idea for a rationalconstruction of spatial structures, and it was successfullyapplied to the structure of World Memorial Hall completedin Kobe in 1984. Pantadome System has since been ap-plied to the Sant Jordi Sports Palace in Barcelona, the Na-tional Indoor Stadium of Singapore and some importantstructures of wide spans realized in Japan. The principle of

Pantadome System is to make a dome or a domical struc-ture geometrically unstable for a period in construction sothat it is 'foldable' during its erection. This can be done bytemporarily taking out the members which lie on a hoopcircle. Then the dome is given a 'kinematic mechanism',that is, a controlled movement, like a 3-D version of a paral-lel crank or a 'pantagraph' which is popularly applied to draw-ing instruments or a power collector of an electric car (hencethe name, 'Pantadome'). By 'folding' the dome in this way,the constituent members of the dome can be assembledon a lower level. The assembly work is thus done safely,quickly and economically, since it can be carried out nearthe ground level. Since the movement of a Pantadome dur-

ing erection is a 'controlled one' with only one freedom ofmovement in the vertical direction, guying cables or brac-ing members which are indispensable in conventional struc-tures to assure their lateral stability against wind or seismicforces are not necessary in erection of a Pantadome struc-ture. The movement and deformation of the whole shape ofthe Pantadome during erection are three dimensional andmay look spectacular and rather complicated, but theyare all kinematically determinate and easily controlled.Three kinds of hinges are incorporated in the PantadomeSystem which rotate during the erection. Their rotationsare all uni-axial ones, and of the most simple kind. There-fore, all these hinges are fabricated in the same way as

normal hinges for usual steel frames.


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Rocking Stones

Rocking stones are stones originally created by Naturethat are movable by human power, or at least looking tobe movable. Here is an example of artificial rocking stoneof 36tons that can be moved by a little child. Repetitivepush of the child in tune with the period of the rockingstone brings the stone into a motion of slow but significantamplitude.

Flying Carp

The "KOINOBORI" is a Japanese traditional carp made offabric which people fly in the breeze in early days of Mayevery year to celebrate the growth of children. The normalsize of a KOINOBORI is 2 to 5 meters in length. KAZO is atown in the suburb of Tokyo that has been famous for itsproduction of KOINOBORI since more than one hundredyears ago. We can still see excellent craftsmen who hand-paint beautiful KOINOBORIS in factories of KAZO City.

In 1988 volunteers of KAZO City, who were members ofJunior Chamber International, got an idea of fabricatingand flying a gigantic KOINOBORI of 100m to advertisetheir city to the world. However, they did not know how toproduce such a huge carp properly. They did not evenknow if such a monstrous feature might "fly" in the air at all.

The author had an opportunity to assist them by estab-lishing the technical basis for the possibility of flying thisgigantic fabric fish in the air. He showed by theory as wellas experiments that a huge KOINOBORI could be de-signed to fly in the breeze of the same wind speed atwhich normal carps fly. By this design theory and struc-tural details a huge KOINOBORI was designed, it wasfabricated by the voluntary members of KAZO City, andfinally it succeeded to fly elegantly in the sky. Since thenflying of the Jumbo KOINOBORI became an annual eventof KAZO City, being celebrated in the beginning of Mayevery year.

Conclusive Remarks

Moving aspects of structures have been described. Al-though structures are normally regarded stationary, thereare many cases where structures move significantly. Themost undesirable motion of a structure is the one due to

collapsing effects of external agencies such as snow, earth-quake, terrorism and deterioration of materials. Structuressometimes produce uncontrolled motion due to wind ef-fects The most dramatic motion is observed when struc-tures show self-excited vibration often started by KármánVorticies as in the catastrophic example of Tacoma Nar-rows Bridge. Since the task of structural engineers is tocreate strong and safe structures, we should be aware ofthose undesirable movements and should always try tofind the means to cope with those phenomena. Some-times we can make the motion of structures controlledone. This can be achieved by means of seismic isolationto cope with earthquakes, and general dampers to cope

with other vibrational effects.

We can also design the structures so that they experiencesignificant movements in the process of construction forthe sake of safety, efficiency and economy of construction,as in the example of Pantadome System. Movement issometimes the intended function to be performed by a struc-ture. One of such cases is an artificial rocking stone of

36tons which the author designed to be moved by a littlechild. Another example is a huge fabric carp of 100m inlength that can fly in the breeze, fabricated by volunteers ofa small town in the suburb of Tokyo under the technicalguidance of the author.

Although it is impossible for those volunteers of the smalltown to make a jumbo jet aircraft, they could fabricate acarp which is much bigger than Boeing 747, and fly it in thebreeze of Kasiserslautern in Germany as well as of theirhometown where they have been playing with it for eigh-teen years.

Author Affiliation

Mamoru Kawaguchi, KAWAGUCHI & ENGINEERS,[email protected]

References

1. A. Beles et al (1966), "Some Observation on the Failure of a

Dome of Great Span", st International Conference of Spade

Structures, University of Surrey

2. S. Montague (1985), "Milan Roof is Total Write Off", New Civil

Engineer, April 25

3. E.B.Farquharson, et al., "Aerodynamic Stability of Suspension

Bridges with Special Reference to the Tacoma Narrows Bridge"Bul. Of Univ. Washington Eng. Exp. Station, No.116, 1949-1954.

4. M. Kawaguchi, I. Tatemichi (2000), "Seismic Isolation Systems

and Their Application in Space Structures", IASS Symposium

on Bridging Large Spans; From Antiquity to the Present,

Istanbul

5. M. Kawaguchi, I. Tatemichi (2000), "Characteristics of A Space

Structure Seismically Isolated by Rocking Pendulums", IASS-

IACM 2000, Fourth International Colloquium on Computation

of Shell & Spatial Structures, June 2000, Chania, Greece

6. M. Kawaguchi (2003), "Physical Models as Powerful Weapons

in Structural Design", IASS Symposium on Shell and SpatialStructures from Models to Realization, Montpellier, Septem-

ber, 2003

Fig. 1 Bucharest Dome before

Collapse

Fig. 2 Dome after Collapse

or Big Motion


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Fig. 3 Palasport beforeCollapse

Fig.4 After Big Motion due toRing Buckling

Fig. 5 Oscillating TacomaNarrows Bridge

Fig. 6 Kármán Vorticies inWind T. Test

Fig.7 Different Pendulums

Fig.8 Concept of Isolated Floors

Fig.11 The Effect of Isolation

Fig.12 Paddle Isolator

Fig.9 Paddle Isolator

Fig. 10 Dimensions

of Isolator

Fig.13 The Both Paddle Isolators Have the Same Period of

Vibration


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Fig. 14. Non-vertical Hoisting of A Dome

Fig. 17 Comparative Dimension of 100m long JumboKOINOBORIFig. 15 Rocking Stone in Colorado, USA

Fig. 16 Art ificial Rocking Stone in Tsukuba


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Consequences of Ignoring orMis-Judging the Size Effect in

Concrete Design Codes and Practice

Abstract

Except for huge unreinforced structures, Weibull's statisti-

cal size effect is weak in concrete structures. The size ef-

fect source is principally energetic, caused by stress redis-

tribution due to a large fracture process zone size or large

cracks formed before maximum load. It is shown that an

unbiased statistical analysis of the existing database for

shear of R.C. beams without stirrups supports the energetic

size effect theory, and that the size effect, albeit milder, af-

flicts beams with stirrups, too. Known though has this type

of size effect been for 24 years, it has been mostly ignored

in design codes as well as practice. What are the conse-

quences? -overdesign of many small structures but, more

seriously, unacceptable risk for large ones. A tolerable fail-

ure probability of engineering structures is 10-6 per lifetime,

and collapse statistics indicate that this has indeed been

true for small structures. Probabilistic analysis calibrated

by a large statistical database confirms this level of failure

probability for shear of reinforced concrete beams without

stirrups < 0.2 m deep. However, if the size effect is ignored

(as in ACI code), the failure probability is shown to increase

drastically-to 10-3 for beams 1 m deep (and nearly as much

for the unrealistic underestimating formulae of CEB, fib and

JSCE). This finding roughly matches several statistics show-

ing that very large structures have been collapsing with a

frequency roughly 103-times greater than small ones. This

is unacceptable. Now that no longer just a handful of theo-

reticians, but entire scientific societies and concrete frac-

ture committees (IA-FraMCoS, ASCE-EMD, ACI Comm.

446), are convinced of the inevitability of energetic size ef-

fect in brittle failures of concrete structures, the engineer-

ing societies ignoring or severely underestimating the size

effect in their design codes, and perhaps even design firms,

are exposed to serious legal risk when another collapse

occurs.

Keywords: size effect, structural safety, reinforced concrete,shear failure, fracture, statistical analysis of test data, de-

sign codes, legal risk.

Introduction

Concrete structures much larger than the specimenstested in laboratories are being built in ever increasingnumbers. For example, the box girder of the record-spanKoror-Babeldaob Bridge in Palau, which collapsed in abrittle shear-compression mode, was 14.2 m deep. Theoutriggers of the Trump Tower under construction in Chi-cago are 6 m deep. However the experimental databasescollected to establish design code specifications consistmostly of small-size laboratory tests. The mean beamdepth in the ACI-445 database (1) on which the sheardesign in the current ACI standard 318 still rests is only0.34 m, and in the latest ACI-445 database (2) it is 0.345m. In the latter, 86% of the 398 data points pertain to beam

depths < 0.5 m and 99% to depths < 1.1 m, and only 1%to depths from 1.2 to 2 m. Since the code-making com-mittees prefer to rely on experiments only, it is thus nosurprise that the size effect is not correctly represented.

Concrete is an archetypical quasibrittle material whosefracture propagation is characterized by a rather largefracture process zone (FPZ), typically 0.5 m long. Thiscauses that small structures (cross section ? FPZ length)fail in a quasi-ductile manner (i.e., with a plastic yield pla-teau) and exhibit almost no size effect, while very largestructures (>> FPZ length) failing in concrete rather thansteel behave in an almost perfectly brittle manner, with a

steep load drop right after the peak load, and exhibit thestrongest possible size effect (3-6); Fig. 1. The size effecthas been most studied for shear of longitudinally rein-forced beams without stirrups (7, 8), but it also occurs inshear of beams with stirrups, in torsion, punching of slabs,failure of columns, arches and prestressed girders due toconcrete compression, failure of anchors and splices, andbar pullout (8, 9). Accumulating experimental evidence(10-20) shows that the size effect causes beams about 2m deep to fail at loads much lower than that calculatedfrom the design code using the understrength factor ϕ =0.75 and the required concrete strength (about 30% lessthan the mean strength). For instance, the largest beam

in Toronto tests (3, 4) had a shear strength almost 50%

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lower than what is calculated from ACI design code (21);see Fig. 1(a). This strength reduction due to size effectnow causes serious concern about the safety of currentdesign codes and engineering practice.

To make the risk of structural failure much smaller thanvarious inevitable risks that people face, the maximum tol-erable failure probability is about 1 in a million (22). Thisvalue roughly agrees with the frequency of failures experi-enced for small beams. But for large ones, it has been about1 in a thousand (23, 24) and could become 1 in a hundredor higher as ever larger beams are being built. Whether ornot such unacceptable risk will have to be tolerated de-pends largely on taking the size effect properly into account.This is an issue of paramount significance for concrete en-gineering.

Risk of Failure in Shear Design

The ACI Building Code (21) currently specifies the contri-

bution of concrete to the cross-section shear strength ofreinforced concrete members by the formula

(1)

(which is valid only in psi, lb. and inches). Here f'c is therequired compression strength of concrete, d is the beamdepth measured from the top face to the longitudinal re-inforcement centroid, and bw is the web width. The codeformula gives a size-independent average concrete shearstrength, v

c= V

c/ b

wd (identical to the 'nominal strength'

in mechanics terminology). However, ignoring the size ef-

fect in Eq. (1) would lead to statistically dangerous de-signs with insufficient safety margins for large shear-criti-cal concrete beams. We evidence it next.

Recently, a database of 398 tests, serving as the experi-mental foundation for the improvement of current sheardesign formula, was compiled by ACI subcommittee 445F(2) and named ESDB. Representing an extension of the1984 Northwestern University database of 296 data (7), itcollects 398 shear strength data for longitudinally rein-forced three-point-bend concrete beams with no stirrups(the Japanese tests reaching the record depth of d = 3 mwere excluded by ACI 445 from this database because

the load was uniform rather than concentrated at midspan).

In Fig. 2(a), the data in the size range of d from 0.1 to 0.3 m,centered at 0.2 m, are isolated from the database. Withinthis narrow range, no size effect trend is discernible, andso the data may be treated as a statistical population. Themean and coefficient of variation of the data

on within this range are

and ω=25% (this relatively high value

of ω is the consequence of unsystematic, haphazard, vari-ability of many influencing parameters in the database). The

values of and ω suffice for determining the probability

density distribution function (pdf) of y in this range. Thepdf is assumed to be log-normal. In that regard, note thatif the randomness of failure loads of small plastically be-having specimens was caused only by the inevitable in-herent randomness of material strength, the only correctchoice of pdf would be the normal (or Gaussian) distribu-

tion (25). In the case of general design formula, however,the major contribution to the scatter seen in Fig. 2(a) stemsfrom the variation of influencing parameters such as theshear span ratio a/d, steel ratio ρw and steel arrangement,aggregate size da, concrete mix, age of concrete, historyof humidity and temperature, etc. The variability stem-ming from these parameters apparently follows moreclosely the log-normal than normal distribution.

The same pdf is compared in Fig. 2(a) to the series ofindividual tests of beams of various sizes made at theUniversity of Toronto (3, 4), which have been invoked bysome engineers to claim that the size effect may be ig-

nored for d up to 1 m (for this depth, the shear strength ofthe Toronto beam lies just above where =

0.75 = understrength factor).

Now it should be noted that, for the type of concrete, steelratio, shear span ratio, etc., used in the Toronto tests, theirshear strength value lies (in the logarithmic scale) at cer-tain distance a below the mean of the pdf. Since the widthof the scatter band in Fig. 2(a) in the logarithmic scale doesnot vary appreciably with the beam size, the same pdf andthe same distance a between the pdf mean and the Torontodata must be expected for every beam size d, including the

sizes of d = 1 m and 1.89 m, for each of which there is onlyone data point. In other words, if the Toronto test for d = 1m were repeated for many different types of concrete, steelratios and shear span ratios, humidity and temperatureconditions, etc., one would doubtless obtain a pdf shifteddownwards, as shown in Fig. 2(a). Now, according to thelog-normal pdf shown, the proportion of unsafe 1 m deepbeams would be about 40%, while for small beams, it isonly 1%. 40% is certainly intolerable. A design code knownto have such a dangerous property is unacceptable.

A design code ignoring the size effect for beams of d < 1m will cause the failure probability P

fof 1 m deep beams to

be about 103-times larger than that of small beams 0.2 mdeep. To demonstrate it, one needs to consider also thepdf of the extreme loads expected to be applied on thestructure, which is denoted as f(y). Based on the load fac-tor of 1.6 and the understrength factor of ϕ= 0.75, the meanof the pdf of the extreme loads will be positioned as shownin Fig. 2(b). Assuming the individual loads to have the log-normal distribution, their pdf is as shown in Fig. 2(b). Basedon the coefficient of variation of extreme loads, here as-sumed as ωL = 10%, the failure probability may now becalculated from the well-known reliability integral (26-28)

(2)

Consequences of Ignoring or Mis-Judging the Size Effect in Concrete Design Codes and Practice

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where R(y) is the cumulative probability density distribu-tion (cdf) of structural resistance. Upon evaluating thisintegral, one finds the following failure probabilities:

for beams 0.2 m deep: for beams 1.0 m

deep:

The failure probability of 1 in a mill ion corresponds to whatthe risk analysis experts generally consider as acceptable(22-24). But 1 in a thousand is unacceptable. So, if the sizeeffect in beam shear were ignored for beams without stir-rups up to 1 m deep, the probability of failure for 1 m depthwould be about 103-times greater than for 0.2 m depth.This would be unacceptable. If there should be any differ-ence, it should be in the opposite sense because, for largebeams, the consequences of collapse are generally moreserious than for small ones.

Statistical Analysis Overcoming Bias in theDatabase

Sound arguments for a realistic design formula capturingthe size effect on shear strength of beams must be basedon fracture mechanics, verified by properly designedexperiments, and statistically calibrated by a broaddatabase. For many engineers, though, a purely statisticalevidence, with no use of mathematics and mechanics, ismost convincing. Such evidence can be, and has been,readily provided for many design problems whereexperiments are easy to perform through the entire rangeof all parameters. But the problem of size effect is different.

In the case of size effect, it is financially prohibitive to con-duct experiments through the entire range of beam depthsof practical interest, which spans from 0.05 m to perhaps14 m (the latter being the depth of the record-setting boxgirder in Palau, whose compression-shear collapse mustbe partly attributed to size effect). Obtaining statisticsand covering by experiments the full range of influencingparameters other than the size (or beam depth) has beeneasy for small beams, but is almost impossible for verylarge ones. Thus it is not surprising that the existing ACIdatabase has major gaps and a strong subjective statis-tical bias caused by crowding of the test data in the small-

size range, scant data in the large size range, and no dataat all for the largest sizes of practical interest (depths >2m). Consequently, simple bivariate statistical regressionof all the points of the ACI-445F database yields a mis-leading trend (29). Eliminating the bias is important for arealistic update of the code provisions currently underconsideration for the design codes of many countries.

The size effect is defined as the size dependence of thenominal strength of structure when geometrical similarity ismaintained and all the parameters other than the size arekept constant. In the case of beam shear, the size maymeasured by the beam depth d, the nominal strength of

structure may be taken as the average concrete shear

strength in the cross section, vc, and the parameters that

must be kept constant comprise all the concrete proper-ties (including the maximum aggregate size d

a), the lon-

gitudinal reinforcement ratio ρw, and the shear span ratioa/d (a = distance of the load from the support).

If the entire database on size effect in beam shear were tobe obtained in one testing program in one laboratory, asound statistical design of size effect experiments woulddictate choosing the same number of tests in equally rel-evant size intervals and maintaining within all the size inter-vals the same means and distributions of parameters ρw,a/d, d

a,, over their entire practical range. This condition is

far from satisfied by the existing database. But there is noother choice. So the question is how to minimize the statis-tical bias in regard to the size effect. From the size effectviewpoint, this database has a bias of two kinds:

o Kind 1. Crowding of the data in the small size range -86% of the 398 data points pertain to three-point-loadedbeams of depths less than 0.5 m, and 99% to depthsless than 1.1 m, while only 1% of data pertain to depthsfrom 1.2 to 2 m.

o Kind 2. Strongly dissimilar means and distributions,among different size intervals, of the subsidiary influ-encing parameters, particularly the steel ratio ρw, shearspan ratio a/d, and the maximum aggregate size d

a.

To reach any meaningful statistical conclusion on the sizeeffect, both kinds of bias must be filtered out.

Statistical Regression of Size Effect

We want to isolate the trend of size effect from a databasegoverned by multiple variables. The standard way to dothat is to carry out multivariate least-square nonlinear re-gression in which all the parameters are optimized simulta-neously. This is the approach which was pursued in previ-ous work (29, 30). There is another way, though. It does notlead to multivariate regression, yet makes the statisticaltrend conspicuous without any mathematics. To this end,an unbiased (i.e., objective) procedure of data filtering isrequired.

Let us subdivide the range of beam depths d of the exist-

ing test data into 5 size intervals (vertical strips in Fig. 3(a-c)). They range from 0.075 to 0.15 m, from 0.15 to 0.3 m,0.3 to 0.6 m, from 0.6 to 1.2 m, and from 1.2 to 2.4 m. In the

ACI database, these intervals contain 26, 251, 80, 38, and3 data points, respectively; see Fig. 3(a-c). Note that theborders between the size intervals are chosen to form ageometric (rather than arithmetic) progression becausewhat matters for size effect is the ratio of sizes, not theirdifference (to wit, from d = 0.1 to 0.1 + 0.5 m, the sizeeffect is strong, from 10 to 10 + 0.5 m negligible). The cho-sen intervals are constant in the scale of log d, and this is

also needed for another reason - in the plot of y =

versus d (Fig. 3), the database is heteroscedastic (i.e.,


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has a variance density decreasing with size), but transfor-

mation to the plot of log versus log d renders

the database almost homoscedastic (i.e., of uniform vari-ance density), which is necessary for meaningful regres-sion analysis (31). Fig. 3(a-c) shows the restricted (filtered)data points by bigger circles, and those filtered out by thetiny circles.

The problem with the distribution of subsidiary influenc-ing parameters in the full database is graphically docu-mented by Fig. 4(a,b), in which the diamonds show theirmeans in the individual size intervals, and the error barsshow the span from the minimum to the maximum re-tained value (Fig. 4(c-f) shows the same plots achievedby filtering the database). In Fig. 4(a), the mean of ρ

wis in

the second interval nearly 7-times larger than in the lastinterval (and almost 2-times larger than in the fourth inter-val). In Fig. 4(b), the mean of a/d is in the third interval 30%

larger than in the last interval (and 10% larger than in thefourth interval). Obviously, such differences among sizeintervals must completely distort size effect statistics.

To filter out the effect of influencing parameters other thand, each interval of d must include only the data within acertain restricted range of ρ

w-values such that the average

would be almost the same for each interval of d. Similarly,the range of a/d and da in each interval must be restrictedso that the average and would also be about the samefor each interval of d. The filtering of data must be done inan objective manner (i.e., with no human preference). Tothis end, a computer optimization algorithm has been for-

mulated. It progressively deletes from each interval, one byone, the data points in each size interval that lie at the topand bottom margins of the ranges of ρ

w, a/d and d

a, until

uniformity of each subsidiary influencing parameter through-out all the intervals is optimally approached. 40%

Because, as generally agreed, the effect of the requiredconcrete strength f'

cis adequately captured by assuming

the shear strength of cross section, vc, to be proportional to

, we do not need to restrict the range of f'c

and may obtainthe ordinate of data centroid in each interval by averag-ing, within that interval, not the vc-values but the valuesof that fall into the aforementioned restricted

ranges of ρw, d/a and da.

As seen in Fig. 3, there are only three test data in the sizeinterval spanning 1.2 to 2.4 m. The first has the longitudinalsteel ratio of ρ

w= 0.14%, the second 0.28% and the third

0.74%. The extremely low ρw

of the first two makes it impos-sible to find similar data in other intervals of d. For example,the minimum ρ

wis 0.91% within the first interval of d, and

0.46% within the third interval. Therefore, one must con-sider the size range from 0.075 to 1.2 m. Formulating a sta-tistical optimization algorithm for database filtering (to bepresented in a forthcoming journal article), one finds 7, 68,17, and 36 data points within the admissible ranges for each

interval of d (ideally, of course, the number of data in each

interval should be the same, and the fact that it is notshows that complete elimination of statistical bias is im-possible; nevertheless for obtaining reliable means, 7 datacertainly suffice).

After filtering, the mean values of ρw

for the restricted rangesare 1.51%, 1.5%, 1.5%, and 1.5%, the mean values of a/dare 3.45, 3.33, 3.33 and 3.23, respectively, and the meanvalues of da are 16.8, 17.0, 16.8 and 16.5 mm. This pro-vides data samples with minimum bias in terms of ρ

w, a/d

and da. The data centroids for each interval are plotted as

the diamond points in the plot of versus log

d (Fig. 3(d)). We see that, despite enormous scatter in thedatabase (Fig. 3(d)), the trend of these centroids is quitesystematic.

Under the assumption that the statistical weight of eachsize interval centroid in Fig. 3 is the same, the foregoingprocedure is used to obtain the optimum least-square fit ofthese 4 centroids with the classical size effect law (type 2energetic size effect law (32)), which was proposed for beamshear in 1984 (7) and recalibrated in 2005 (30), and is

written here as where C,

d0 = free constants to be found by the fitting algorithm(for reasons of proper weighting, it is best to conduct non-linear regression with a nonlinear optimization subroutine,although a linear regression in transformed variables ispossible and acceptable (9)). The resulting fit of the cen-troids (the solid curve) is seen to be quite close; it gives,for predicting the mean strength, a very small coefficient

of variation of errors, namely ω= 2.5% = standard devia-tion of the optimum fit curve from the centroids, dividedby the data mean (for individual beams, ω is, of course,much larger). This coefficient of variation characterizesthe uncertainty in the mean strength of many structures ofa given size rather than in the strength of an individualstructure, which is of main interest for design. The nega-tive curvature of the trend of the centroids confirms thetheoretically predicted (8) gradual transition from quasi-plastic behavior for small sizes to perfectly brittle behav-ior for large sizes. The trend of the last two centroids roughlymatches the theoretical prediction of the slope -1/2 of thefinal asymptote of the size effect curve, given by vc ~ d -1/

2 (7, 13, 29, 30, 32) (which is a property unanimously en-dorsed as fundamental in 2004 by ACI Committee 446).

Using the same statistical algorithm, let us now increasethe average steel ratio for each interval to 2.5%. The fittingof the centroids is shown in Fig. 3(e). The asymptotic slopeof -1/2 is confirmed and the negative curvature is obvious.

To increase the size range, one may further include onepoint from the largest size interval spanning 1.2 to 2.4 m,namely the Toronto beam with

w= 0.74%; see Fig. 3(f).

Admittedly, one data point is too little, but nothing moreexists because of the cost of testing very large beams. Then

the same procedure as above is followed and, for the other


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4 intervals of d, one finds 1, 2, 5, and 15 data points forwhich the means of ρ

win the interval of d are 0.91%, 0.94%,

0.94%, 0.91% and 0.74%, while the mean of a/d (= 2.9)and the mean maximum aggregate size da (= 10 mm) arethe same for each interval. The coefficient of variation oferrors of mean prediction now is ω= 5%, and the size effect

trend is very clear. Again, the trend agrees well with theasymptotic slope of -1/2 and with the energetic size effectlaw (solid curve, Fig. 3(f)).

Now, an important point to note is that, for different aver-ages , and , the trend of the interval centroids is thesame, and closely matches the size effect law. This dem-onstrates objectivity of the data filtering approach.

Also note that the present statistical results lend no sup-port to the previously proposed power laws based onWeibull's statistical theory (33). Neither do they lend anysupport to the asymptotic size effect which is implied byan alternative model (34, 35) based on MCFT (ModifiedCompression Field Theory) (besides, an exponent of mag-nitude >1/2 is impossible thermodynamically as well as fromthe viewpoint of material strength randomness (8, 9, 36)).

Variance of Individual Data Via Weighted Regression:Kinds 1 and 2 of bias afflict not only the mean trend of thefull database, but also its scatter. The scatter may be mea-sured by an unbiased coefficient of variation of the errorsof the optimum fit curve compared to the individual datapoints. This is the error that must be considered for safedesign. It can be ascertained by one of two methods:

1) One method is a simple bivariate nonlinear regression

of our filtered restricted database, in which the kind 2 biasis already suppressed. To suppress the kind 1 bias, oneneeds to give the same weight to the data in each sizeinterval i, regardless of the number mi of the points thatfall into that interval. This may be achieved by assigningto the data in each interval i the normalized weight .Nonlinear regression, i.e., the minimization of the weightedsum of square deviations from the size effect law, thenyields the coefficient of variation of 22.3% for the filtereddatabase with =1.5%, and 23.6% for that with = 2.5%(Fig. 5).

2) The other method, which is the standard one, is a mul-

tivariate weighted nonlinear regression of the entire data-base. Compared to the first method, there is the compli-cation that, instead of filtering the database, one mustjudiciously select the mathematical function describingthe dependence of the parameters C and d0 of the sizeeffect law for shear strength on the subsidiary influencingparameters ρ

w, a/d and d

a, and then optimize simulta-

neously the coefficients of all these functions by minimiz-ing the variance of errors. Proper choice of these functionssuppresses the kind 2 bias. The kind 1 bias is in ref. (30)minimized by weighting the data points in inverse propor-tion to the value of a smoothed histogram of the number oftests versus size. The result is quite similar to the first

method - the coefficient of variation is 19.0%, after trans-

formation to the variable . However, the range from theminimum to the maximum value of each subsidiary pa-rameter (Fig. 4) fluctuates, from one size interval to thenext, more than in the first method (ideally, the rangeshould be the same for all the intervals, and the fact that itis not introduces some extra measure of bias, which can-not be removed although it probably is small).

The effect of data weighting can further be clarified byFig. 5(a,b) where the solid curves are the bivariate nonlin-ear regression curves of the interval centroids, with thesame weight on each centroid. As one can see, almostundistinguishable curves (dashed ones) are obtained bythe weighted nonlinear bivariate statistical regression ofall the data points in the restricted (filtered) database. Anunweighted regression of the same data points is shownin Fig. 5 by the dash-dot curves, and, as we can see, thedash-dot curve is again hardly distinguishable from theregression curve of the centroids in Fig. 5(a), but is very

different in Fig. 5(b). One reason for this difference is thatthe vertical ranges of the restricted data in the individualsize intervals, marked by vertical bars, are in Fig. 5(a) nearlysymmetric with respect to the centroid curve, but not inFig. 5(b). Another reason is that the restricted database inFig. 5(a) is roughly homoscedastic, while that in Fig. 5(b)is not.

For comparison, the coefficient of variation of the multi-variate nonlinear regression conducted on the entire da-tabase (2) is 15% if the data are weighted, and 17% ifunweighted. When only the 11 beams deeper than 1 mare considered, the coefficient of variation is 14% if thesedata are weighted and 16% if unweighted. As we see, theweighted regression gives a better prediction for the scat-ter of shear strength of large beams.

Size Effect For Concrete Beams With Stirrups

Although much information exists on the size effect onreinforced concrete beams without shear reinforcement,there is little information on the size effect in shear failureof beams with minimum or heavier shear reinforcement(stirrups). Many engineers are of the opinion that beamswith minimum or heavier stirrups exhibit no size effect.However, this opinion is incorrect and would lead to un-safe designs for large structures. Computational simula-

tions, and even the limited experimental evidence thatexists, reveal that stirrups do not eliminate the size effect.They only mitigate it. According to the analysis by Ba•ant(37), the energetic size effect law (32) remains valid andthe effect of stirrups is to increase the transitional size d0(9). Avoidance of size effect would require elimination ofpost-peak softening on the load-deflection diagram, andthis could be achieved only if the concrete were subjectedto triaxial confinement with all negative principal stressesexceeding in magnitude several times the uniaxial com-pression strength.

The test series conducted by Walraven et al. (19) clearly

show that there is a strong size effect for deep beams with


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a/d < 2 (Fig. 6(a)) to which the strut-and-tie model is ap-plicable. As is well known, if the failure is triggered by thecompression crushing of concrete strut, it typically exhib-its size effect (8). For slender beams with a/d > 2, two testseries are found in the literature:

1. tests conducted by Bhal (11) in 1968 in Stuttgart, inwhich the shear span ratio is a/d = 3, the shear rein-forcement is heavier than the minimum requirement,and the size range is almost 1 : 4.

2. tests conducted by Kong and Rangan (20) in 1998 inPerth, in which the shear span ratio is a/d = 2.4, theshear reinforcement is heavier than the minimum re-quirement, and the size range is 1 : 3.

When plotted in the logarithmic scale (Fig. 6(b,c)), it canbe seen clearly that, in both data sets, the shear strengthmarkedly decreases with increasing beam depth. The as-ymptotic size effect trend of slope -1/2 does not contra-dict these test results.

Extensive finite element simulations based on the crackband model have also been carried out to investigatewhether the shear failure of beams with stirrups exhibits asize effect. The beam geometry considered in these simu-lations is same as in the Toronto tests (3, 4, 18). Computa-tions are run for geometrically similar beams of depths0.47 m, 1.89 m, which is the size of Toronto test, and 7.56m. The stirrups and longitudinal bars are assumed not toslip (although the bond slip was found to play only a minorrole and tend to intensify the size effect).

The mesh and the computed cracking pattern at maxi-mum load are shown in Fig. 7(a), and the simulated load-deflection diagrams are shown in Fig. 7(b), for all the sizes.The diagram for d = 1.89 m (the size tested in Toronto)shows the peak load of 283 kips. This is very close to thevalue measured in Toronto. The yield plateau observed inthis test is also well reproduced by the simulation. How-ever, for the largest beam simulated, the yield plateaudisappears and the load descends steeply right after thepeak. Fig. 7(c) shows the dependence of the averagebeam shear strength vn = V/bw d on beam depth d, andFig. 7(d) shows the same for the average shear strength

vc = Vc/bw d contributed by concrete (Vc = V - Vs, Vs = As fy d/s; As, s = stirrup area and spacing). Comparedwith the concrete beams without stirrups tested at samelaboratory, the transitional size d0 shown in Fig. 7(c,d) issignificantly increased. These plots document that a strongsize effect exists also in the beams with stirrups, althoughit is pushed into larger sizes. The asymptotic slope of -1/2is seen to remain.

Together with the experimental evidence, the finite ele-ment simulations clearly demonstrate that the shear rein-forcement, whether minimum or heavier than minimum, isunable to suppress the size effect. It mitigates the size

effect in the larger size range, but not enough by far to

make it negligible.

Some Catastrophic Collapses With A Role Of Size

Effect

The overall safety factor µ , although not used in the currentcodes, is defined as the mean of failure test data divided

by the mean (or unfactored) design load. The part of µ ofconcern here is the understrength factor. Besides the overtunderstrength factor j characterizing the brittleness offailure mode, there also exists a covert understrengthfactors jf due to the design formula error and jm due to thematerial randomness (38). Consequently, for shear failureof longitudinally reinforced concrete beams withoutstirrups, the overall safety factor currently is µ ~ 3.8 forsmall sizes and µ~1.7 for large sizes. The former is totallydominated by the live load, and the latter is totallydominated by the self weight. In the latter case, theneglected size effect factor has been considered (38) as

2. In view of the scatter in Fig. 3, the individual overallsafety factors vary within 2.3 to 6 for small sizes, and 1.05to 2.8 for large sizes. The very large values of thesesafety factors are doubtless one reason why, despite theneglect of size effect, there have not been many morestructural collapses than actually experienced. These largevalues also reveal that, in concrete engineering (bycontrast to aeronautical engineering), a single error indesign or construction is usually not enough to bring thestructure down.

The size effect factor for normal concrete structures canhardly be more than 2, and so the size effect alone would

rarely suffice to cause the collapse if the material strengthand formula error have nearly mean values. To producecollapse, the material strength and formula error must si-multaneously have values of small probability, far from themean. Thus, at least two, and typically three, simultaneousmistakes or lapses of quality control are needed to makea concrete structure collapse. This makes it easy for aninvestigating committee to blame collapse entirely on theother factors and ignore the theoretically more difficultsize effect. For example, in the case of catastrophic sink-ing of Sleipner oil platform in a Norwegian fjord in 1991(Fig. 8(a)), which was due to shear failure of a thick tricellwall, there were three simultaneous mistakes. Besides twomistakes recognized by government forensic committee,the necessity of strength reduction of about 34% due tothe size effect was pointed out but omitted from the con-clusions. Of major interest for the size effect theory is the1996 collapse of the Koror-Babeldaob Bridge in the Re-public of Palau (Fig. 8(b)). This prestressed box girderhad the world record span of 241 m when it was built in1976. In addition to the erroneous initial prediction of creepand shrinkage deflections and apparently inappropriateremedial prestressing, one would have to expect a majorstrength reduction due to size effect on the compression-shear failure seen in the photograph. Analysis of this col-

lapse would offer a unique opportunity to check and cali-


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brate the size effect theory but, incredibly, all the techni-cal information was sealed after litigation by a court ver-dict. Scientific ethics demands this verdict to be reversed,in the interest of progress (imagine, e.g., that all the tech-nical information on the collapse of Tacoma Narrows Bridgewere suppressed).

Another reason why structural collapses have not beenmore numerous is that most codes, unwittingly, hide apartial (thought imperfect) protection against size effectin an excessive value of the load factor for self-weight,which is 1.4 for the self-weight acting alone, according tothe current ACI code. In small structures, the self-weight isa negligible part of the load, and so the value of self-weightload factor does not matter. But in a very large bridge,self-weight alone is the decisive loading case. Now, howcould the self-weight be 40% larger than assumed in de-sign? This is inconceivable (except as a sabotage). Atmost it could differ by a few percent. So very large struc-

tures are penalized by almost 40% compared to smallones. This way most codes give a covert protectionagainst the neglect of size effect (39). But such covertprotection is insufficient, by far, for very large structures. Italso exhibits an incorrect trend from the viewpoint of sizeeffect (39), as well as other wrong features. E.g., it givesgreater protection to unprestressed or normal concretescompared to prestressed or high-strength concretes,because they lead to heavier structures, although theopposite should be the case because they are much morebrittle; it gives too little protection to columns comparedto beams, etc. This covert size effect should be eliminated

and replaced by introducing the proper size effect in thecode formulae.

The Question Of Legal Liability Of Concrete Societies

In the face of ever increasing diversification of science, itis nowadays impossible for the code-making committees,typically composed of the best and most renowned engi-neers, to follow in detail all the recently solidified scientificadvances relevant to the building code article or recom-mended practice that they are developing. Nevertheless,keep informed they must. A quarter century ago, when theexperimental data were scant and scattered, and only a

handful of scientists espoused a coherent scientific theory,it was entirely plausible and defensible for concrete soci-eties to ignore the size effect. When a failure attributableto size effect occurred, they could not be held liable. Notany more. The experimental evidence has become unde-niable and the theoretical basis solid. Virtually all the re-searchers in fracture mechanics of concrete and entireresearch-oriented societies and committees in this field(e.g., IA-FraMCoS, ASCE-EMD, ACI Committee 446) haveno doubt that a significant non-statistical size effect existsin all the brittle failures of concrete structures. Conse-quently, ignoring the size effect for the sake of simplicity,or even sanctioning a simplistic or partial consideration of

size effect that is now known to imply a significantly in-

creased risk of failure of large structures, is no longer ac-ceptable. It might expose concrete engineering societiesto legal liability when another catastrophe occurs.

Conclusion

At the dawn of this century, the size effect in brittle failures

of concrete structure has become an established fact. It istime to introduce it into the design codes and practice. Ig-noring it will cause large structures to be failing with thefrequency of about one per thousand or more, instead ofless than one per million as generally considered tolerablefor engineering structures. The human society must not beknowingly exposed to such a risk.

Acknoweldgment: Financial support from the U.S. Depart-ment of Transportation through the Infrastructure Technol-ogy Institute of Northwestern University under Grant No.0740-357-A210 is gratefully acknowledged.

Author Affiliation

Bazant, Zdenek P.: Ph.D., Dr.h.c. mult., S.E. McCormickSchool Professor and W.P. Murphy Professor of CivilEngineering and Materials Science, NorthwesternUniversity, 2145 Sheridan Road, Tech A135, Evanston,Illinois 60208; [email protected] Yu, Qiang:Ph.D, Research assistant, Northwestern University;[email protected]

References

1. ACI-ASCE Committee 326 (1962). "Shear and diagonal tension" ACI Journal, Proceedings Vol. 59, pp. 1-30 (Jan.), 277-344 (Feb.),

352-396 (March).

2. Reineck, K-H, Kuchma, D. A., Kim, K. S. and Marx, S.(2003)."Shear Database for Reinforced Concrete Members without ShearReinforcement" ACI Structural Journal, V. 100, No.2, March-April2003, pp. 240-249.

3. Podgorniak-Stanik, B.A. (1998). The influence of concretestrength, distribution of longitudinal reinforcement, amount oftransverse reinforcement and member size on shear strength ofreinforced concrete members M.A.Sc. Thesis, Department ofCivil Engineering, University of Toronto, 1998.

4. Angelakos, D, Bentz, E.C., and Collins, M.P. (2001). "Effect ofconcrete strength and minimum stirrups on shear strength of

large members" ACI Structural J, 98 (3), pp. 290-300.

5. Bazant, Z.P., Sener, S. and Prat, P.C. (1988). "Size effect tests oftorsional failure of plain and reinforced concrete", Materials andStructures (RILEM, Paris), 21, pp. 425-430.

6. Regan, P.E. (1986). "Symmetric punching of reinforced concreteslabs", Magazine of Concrete Research, V. 38, N. 136, Septem-ber 1986, pp. 115-128.

7. Bazant, Z.P., and Kim, J.-K. (1984). "Size effect in shear failure oflongitudinally reinforced beams" Am. Concrete Institute Journal,81, 456-468; Disc. and Closure 82 (1985), pp. 579-583.

8. Bazant, Z.P. (2002). Scaling of Structural Strength. Hermes Penton

Science, London; 2nd updated ed., Elsevier 2005.


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9. Bazant, Z.P., and Planas, J. (1998). Fracture and Size Effect inConcrete and Other Quasibrittle Materials. CRC Press, BocaRaton and London.

10. Leonhardt, F. and Walther, R. (1962) "Beiträge zur Behandlungder Schubprobleme in Stahlbetonbau" Beton-und Stahlbetonbau(Berlin), March, 54-64, and June, pp. 141-149.

11. Bhal, N.S. (1968) ?ber den Einfluss der Balkenhöhe aufchubtragfähighkeit von einfeldrigen Stalbetonbalken mit und ohneSchubbewehrung. Dissertation, Universität Stuttgart, Stuttgart,Germany.

12. Bazant, Z.P., and Sun, H-H. (1987). "Size effect in diagonal shearfailure: Influence of aggregate size and stirrups" ACI MaterialsJournal, 84 (4), pp. 259-272.

13. Bazant, Z.P., and Kazemi, M.T. (1991). "Size effect on diagonalshear failure of beams without stirrups" ACI Structural Journal 88(3), pp. 268-276.

14. Iguro, M., Shioya, T., Nojiri, Y. and Akiyama, H. (1985). "Experi-mental studies on shear strength of large reinforced concrete

beams under uniformly distributed load" Concrete Library Inter-national of JSCE, No.5 (translation from Proc. JSCE, No. 345/V-1, Aug. 1984), pp. 137-146.

15. Shioya, T., Iguro, M. Nojiri, Y., Akiyama, H., and Okada, T. (1989)."Shear Strength of Large Reinforced Concrete Beams" FractureMechanics: Application to Concrete, SP-118, V.C. Li, and Z.P.Ba•ant, eds., American Concrete Institute, Farmington Hills, Mich.,1989, pp. 259-279.

16. Shioya, T. and Akiyama, H. (1994). "Application to design of sizeeffect in reinforced concrete structures" Size Effect in ConcreteStructures (Proc., Japan Concrete Institute International Work-shop, Sendai), H. Mihashi, H. Okamura and Z .P. Ba•ant, eds.,E\&FN Spon, London, pp. 409-416.

17. Kani, G.N.J. (1967). "How safe are our large reinforced concretebeams?" ACI Journal, 58(5), pp. 591-610.

18. Lubell, A., Sherwood, T., Bentz, E., and Collins, M.P. (2004). "SafeShear Design of Large, Wide Beams" ACI Concrete International26 (1), pp. 67-78.

19. Walraven, J.C. and Lehwalter, N. (1994). "Size effect in shortloaded beams in shear" ACI Structural Journal, V. 91, No. 5, pp.585-593.

20. Kong, P.L. and Rangan, B.V. (1998). "Shear strength of highperformance concrete beams" ACI Structural Journal, 95(6), pp.677-688.

21. ACI Committee 318 (2005). Building Code Requirements forStructural Concrete (ACI 318-05) and Commentary (ACI 318R-05), Am. Concrete Institute, Farmington Hills, Michigan.

22. Duckett, W. (2005). "Risk analysis and the acceptable probabilityof failure" The Structural Engineer, August, pp. 25-26.

23. Melchers, R.E. (1987). Structural Reliability, Analysis & Prediction.Wiley, New York.

24. NKB (Nordic Committee for Building Structures) (1978). Recom-mendation for loading and safety regulations for structural de-sign. NKB Report, No. 36.

25. Bazant, Z.P., and Pang, S.-D. (2007). "Activation energy basedextreme value statistics and size effect in brittle and quasibrittle

fracture". J. of the Mechanics and Physics of Solids 55, 91-134.

26. Ang, A.H.-S., and Tang, W.H. (1984). Probability concepts inengineering planning and design. Vol II. Decision, Risk and Reli-ability, J. Wiley, New York.

27. Madsen, H.O., Krenk, S., and Lind, N.C. (1986). Methods ofstructural safety. Prentice Hall, Englewood Cliffs, N.J.

28. Haldar, A., and Mahadevan, S. (2000). Probability, Reliability and

Statistical Methods in Engineering Design, J. Wiley & Sons, New York.

29. Bazant, Z.P., and Yu, Q. (2005). "Designing against size effect onshear strength of reinforced concrete beams without stirrups. I.Formulation" J. of Structural Engineering ASCE, 131 (12), pp.1877-1885.

30. Bazant, Z.P., and Yu, Q. (2005). "Designing against size effect onshear strength of reinforced concrete beams without stirrups: II.Verification and Calibration" J. of Structural Engineering ASCE,131 (12), pp. 1886-1897.

31. Ang, A.H.-S., and Tang, W.H. (1975). Probability concepts inengineering planning and design. Vol I. Decision, Basic Prin-

ciples, J. Wiley, New York

32. Bazant, Z.P. (1984). "Size effect in blunt fracture: Concrete, rock,metal" J. of Engrg. Mechanics, ASCE, 110 (4), pp. 518-535.

33. Weibull, W. (1939). "A statistical theory of the strength of materials"Proc. Royal Swedish Academy of Eng. Sci., pp. 151, 1-45.

34. Vecchio, F.J., and Collins, M.P. (1986). "The modified compres-sion field theory for reinforced concrete elements subjected toshear" ACI J.. Proc., 83 (2), pp. 219-231.

35. Collins, M.P., Mitchell, S., Adebar, P. and Vecchio, F.J. (1996)."General shear design method" ACI Struct. J., 93(1), pp. 36-45.

36. Bazant, Z.P. (2004). "Scaling theory for quasibrittle structural fail-ure", Proc., National Academy of Sciences 101 (37), pp. 13397-13399 (inaugural article).

37. Bazant, Z.P. (1997). "Fracturing truss model: Size effect in shearfailure of reinforced concrete" J. of Engrg. Mechanics, ASCE123 (12), pp. 1276-1288.

38. Bazant, Z.P., and Yu, Q. (2006). "Reliability, brittleness, covertunderstrength factors, and fringe formulas in concrete dessigncodes" Journal of Structural Engineering, ASCE, Vol. 132, No. 1,pp. 3-12.

39. Bazant, Z.P., and Frangopol, D.M. (2002). "Size effect hidden inexcessive dead load factor." J. of Structural Engrg. ASCE 128(1), 80-86.


Fig. 1 Size Effect Tests of (a) Shear Failure; (b) Torsional

Failure; and (c) Punching Shear Failure

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Fig. 2 (a) Probability Distribution of Shear Strength of Beamsfrom 10 to 30 cm Deep, Based on the ACI-445F database,Compared to Toronto Data; (b) Failure Probability for Small

Beam and 1 m Deep Beam.

Fig. 3 ACI-445F Database and Statistical Regression ofCentroids of Test Data Subdivided into Intervals of Equal Size

Ratio. (a-c) Full Database (the data retained are shown bylarger circles and those filtered out in various cases by tinycircles); (d-f) Filtered Restricted Data Giving the Indicated

Combinations of Uniform Mean Values of Subsidiary

Parameters, Their Centroids and Regression Curves.


Fig. 4 Interval Centroids and Spread between the Maximumand Minimum Value

Fig. 4 Interval Centroids and Spread between the Maximumand Minimum Values of Reinforcement Ratio rw and Shear

Span Ratio a/d ; (a,b) for Full ACI-445F Database; (c,d)for Restricted Database with Mean rw ̃ 1.5%, a/d ̃ 3.3;

(e,f) Ditto but rw ̃ 2.5%, a/d ̃ 3.3; (g,h) Ditto but rw ̃ 0.9%,a/d ̃ 3.0.

Fig. 5 Regression Curves Corresponding to Weighted Fitting(Dashed Curves), Unweighted Fitting (Dash-dot Curves) andFitting on Centroids (Solid Curves) for Filtered Database of

(a) Average Steel Ratio = 1.5%; and (b) Average Steel

Ratio = 2.5%.

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Fig. 7 Computational Simulations of Toronto Beam withMinimum Stirrups. (a) Mesh and Cracking pattern at failure;(b) Load-deflection Curves Generated by Simulations; (c)

Size Effect Fitting of the Total Shear Strength; (d) Size EffectFitting of the Concrete Shear Strength

Fig. 8 Examples of Catastrophic Failures of Concrete Struc-tures. (a) Sleipner Oil Platform, 1991; (b) Koror-Babeldaob

Box Girder in Republic of Palau, 1996.

a) Sleipnerplatform, 1991 b) Palau bridge, 1996

Fig. 6 Size Effect Test of Concrete Beams with Stirrups. (a)Deep Beam with a/d = 1; (b) Slender Beam with a/d = 3; (c)

Slender Beam with a/d = 2.4.


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Damage Identification of StructuresThrough Simple and Measurable

IndicatorsRaghu Prasad B.K, Lakshmanan N,

Gopalakrishnan N and Muthumani K

Abstract

Simple, fast and robust strategies are required for estimat-ing the health of a structure using globally available re-

sponse data. The paper proposes a first stage structuralhealth monitoring methodology using natural frequenciesand static deflections as damage indicators. Equations andmethodologies are proposed and validated in the paper,numerically and experimentally towards damage estima-tion. Identification methodology developed in this paper isapplicable to distributed smeared damage, which is typi-cal of reinforced concrete structures. The idea is that thefirst stage monitoring can be done for a large number ofvulnerable structures in a remote manner and the featuresextracted from the data should help in determining whetherany second stage detailed investigation is warranted. Keywords: Structural health monitoring, Damage Indicators,Bridges and Buildings.

Introduction

A civil engineering structure is a plant (structure or systemwith a governing set of linear or differential equations) whichtakes some input (force) and produces some output (re-sponse). The input could be purely random or determinis-tic. The relationship between the input to output (I/O) de-fines the physical phenomenon that governs its structuralbehavior. This I/O relationship is termed as flexibility (or stiff-ness) in a static structure, compliances (with frequencydependence) in a dynamic structure or an impedance in

an electrical circuit. In many of the situations when a builtstructure or existing mechanical component is to be as-sessed, the I/O relationship has to be generated whole orpart. The problem of identifying this I/O relationship istermed as "system identification". This is typically an "in-verse problem". A good example is a pile foundation, whichis suspect for its load carrying capacity (which cannot beinspected visually) and its state of well being could only beinferred through its response to a set of dynamic or staticforces.

Contrary to a forward problem, the peculiar challenges thatare associated in a system identification and the associ-

ated inverse problem are:

(a) Unwanted signals come in the form of noise both in theinput force as well as in the response and this may bepurely Gaussian or ground-loop electrical noise or dueto other sources (temperature, humidity etc.)

(b) There may be less number of measurements and morenumber of un-known variables (under-determined).

(c) Non-uniqueness of the response, where many possibleinputs could give rise to the same response.

(d) There may be more number of measurements and lessnumber of un-known variables (over-determined).

(e) Less sensitivity of the structure or part of the structure inresponse to impressed forces.

(f) System-non-linearity, friction and other causes, which

are difficult to quantify in precise mathematical terms.

(g) Uncertainty in modeling boundary conditions, joints, andopening-closing cracks (which shows different stiffnessat each half-cycle) and so on.

Previous Investigations on Damage Assessment

Damage-induced variation of static deflection in a beam isused to identify the concentrated damage through an in-verse analysis and closed form expression by Caddemi andMorassi [1] and Caddemi and Greco [2]. Interestingly, theprocedure developed by them, requires measurement of

displacements at both the sides of a concentrated crack toevaluate the crack position. A Monte-Carlo simulation pro-cedure is also used to evaluate the effect of Gaussian dis-tributed measurement errors on the damage evaluationprocedure. The paper by Buda and Caddemi [3], also onsimilar lines, outlines a strategy for damage identificationfor concentrated damage in an Euler-Bernoulli beam. Thestatic damage identification problem is reduced to aFredholm integral equation of the second kind character-ized by a Pincherle-Goursat kernel by Paola and Billelo [4]in another note-worthy work. A simple and elegant formula-tion by Choi [5] and Choi et. al [6], presents an elastic dam-age load theorem, which indirectly states that change in

deflection due to damage is maximum near the vicinity of

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damage and absolute maximum when the position of load,damage and measurement locations coincide.

The available literature on system identification and dam-age detection using only dynamic measured data is huge.

A comprehensive survey is presented by Doebling et al.[7], who have reviewed the numerous technical literaturesavailable on damage detection through vibration testing.Hassiotis et. al. [8], Hassiotis [9] outline a method basedon first order perturbation and optimization theory to com-pute the damage from measured natural frequencies. Iden-tification of damage locations in plate-like structures usingstrain modal approach is proposed by Li et. al [10], usingbending moment index and residual strain mode shape in-dex. A combined static and dynamic approach for damageidentification using curvature mode shape and strain fre-quency response function is proposed by Yam, et. al [11].

The combined static and dynamic data or static-only datafor damage detection are less. Various structural proper-ties of anisotropic composites are identified using prob-ability of detection (POD) concepts and boundary elementnumerical simulation, using static data by Rus et. al [12].Use of wavelets in damage identification using experimen-tally derived deflection through digital photography by Ruckaand Wilde [13] is an interesting study. Nejad et. al [14]have used an optimization method that minimizes the dif-ference between the load vector of the damaged and un-damaged structure using static noisy data for damage iden-tification. A static-dynamic combined damage detectiontechnique, without prior information of intact structure isused by Vanlanduit et. al [15]. Sensitivity studies on static

deflection curvature, curvature mode shape and strain fre-quency response function on damages have been used by

Yam. et. al [16] in yet another interesting study. Anothercombined static-dynamic system identification study usingmeasured damage signature and predicted damage sig-nature is through the work of Wang et. al [17]. Recentlywavelet and radial basis function (ANN) based damageidentification from dynamically measured parameters isproposed by Lakshmanan et al. [18,19] and Raghuprasadet al. [20, 23]. In a previous work Lakshmanan et. al [21,22]have proposed a smeared damage model and the sensi-tivity matrix of static deflection due to damage (reduction of

flexural EI) formulated and solved as an over-determinedsets of equation.

Definition of Damage

A structure is deemed to have been damaged if the struc-ture, after un-loading could not return to its original stateand there is a permanent deformation with loss of energy.Damage is defined, as per International Standards Organi-zation, "as an unfavorable change in the condition of a struc-ture that can affect the structural performance". A structuralmember can suffer varying degrees of damage due to rea-sons such as over loading, environmental ageing, corro-

sion, poor quality of construction, fatigue crack growth un-

der cyclic loading, and creep. On many occasions, a main-tenance engineer is required to take decisions regardingthe repair and improvement of the damaged structure. Theviability of repair has to be weighed with the cost of newreplacement and this is governed by the state of damagesuffered by the structure. Estimation of the magnitude of

damage, location and its spread thus plays a crucial role inthe repair methodology to be adopted. Also, residualstrength and remaining life depend on the magnitude andposition of damage. Structural health monitoring (SHM) isa field of science dealing with the mathematics, algorithms,instrumentation, data-analysis and feature extraction meth-ods for damage identification of structures. SHM providesan engineer with mathematical, structural and electronictools such that damage could be measured and quanti-fied. This is analogous to a doctor provided with variousdiagnostic tools for identifying the health of a human being.

The methodology adopted for identification should be

simple, both in terms of investigations involved and the in-strumentation. Researchers have proposed various meth-odologies including damage identification from modeshapes, wavelet-based formulations and optimization-based damage identification and instrumentation schemesand so on. These are technically involved but require moremeasurements for all critical bridges/buildings, where thesheer volume of number of structures to be investigated isenormous. Ideally, structural health monitoring has to becarried out in two stages:

(a) Stage-1: Remote monitoring of global damage indica-tors and inference of the health of the structure. Instru-

mentation for this stage should be less, simple, but atcritical locations to capture the global damage in a rea-sonable sense.

(b) Stage -2: If global indicators show deviation beyond aspecified threshold, then a detailed and localized instru-mentation and monitoring, with controlled applicationof static and dynamic loads is to be carried out to inferthe health of the structure and take a decision on therepair and retrofit strategies.

Damage Identification from Natural FrequencyChange

In this section, another method based on contours of equalfrequency change, named, "Iso_Eigen_value_change con-tours" is proposed. It is shown that the intersection of twoor more contours with ratios of frequency changes betweenmultiple pairs of frequencies shall give the position andextent of damage. It may be proved that the ratio of thechanges in natural frequencies for any pair of modes (sayN and M-th modes) remains constant irrespective of themagnitude of damage, '?'. However, the criterion is valid fora single contiguous damage and many researchers haveapplied this methodology to concentrated damage idealisedby a rotational spring. The extension of this method for a

distributed damage covered here is novel and unique.

Damage Identification of Structures Through Simple and Measurable Indicators

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Necessary equations for drawing Iso_Eigen_value_changecontours are developed using first-order perturbation theory.

Analytical validation of these curves is carried out for simu-lated damage values. Fig.1 shows the parameters that de-fine a damage.

Damage Identification From

Iso_Eigen_Value_Change Contours

Fig. 1 Simply supported beam with a reduced EI for portion

of its lengthGenerally, damage due to over-loading of a structure, af-fects certain definite length of the structure, which is con-tiguous. The distribution of damage, over this affected lengthcould be in some known variation, say, less at ends of dam-age zone and more at the centre of the damage. Henceidentification of the parameters that define a single con-tiguous damage is more relevant as generally damage doesnot happen in some abrupt variation along a structural ele-ment. The knowledge of at least three frequency changesare essential for retrieving the unknown parameters, whichdefine a damage. Hence the strategy is to eliminate ? bytaking the ratio of the change in frequencies for two naturalmodes. Ratio of the changes in Eigen values are obtainedafter modifying and re-writing relevant equations as,

(1)

hence it is inferred that the ratio of changes in Eigen val-ues, for two modes 'n' and 'm' (squared frequencies) areindependent of the magnitude of damage and are func-

tions of only the central position of damage and its extent.Indirectly, the method is to find out the ratio of variation in

frequencies as the normalizing factor which

is a constant for any pair of frequencies. Having eliminateda variable (β ), out of three, it is possible to construct curvessuch that the variation of Eigen-change-ratios can be visu-

alized. Varying values of which give rise to con-

stant Eigen-change-ratios

for a simply supported beam are plotted in the form

of contours. Following physical in-sights can be obtainedfrom the general contours :

Contours are symmetrical indicating that a symmetrical

damage affects the frequencies equally.

The boundary line shows that the extent of damage ,

on the Y-axis shall at best be twicehe centre of damage

location , on the X-axis.

Contours at the top most point indicate a wide-spread

constant damage and all frequencies are affectedequally and hence the ratio is 1.0.

Contours closer to support are around 3 to 4, indicating

that high frequencies are affected more by off-centricdamage.

As a converse of point (d), contours closer to mid-span,

show smaller values especially for small amounts ofdamage.

This exercise on the theoretical damage identification studyinvolves certain example validation problems which aresolved using these contours.

The example validation problems (D1 to D2) solved are asfollows : ( is the magnitude of damage, kept as 0.10)

(a)D1: (b) D2:

For example, in case(a) 2

2

2

2

n

m

m

n ww

ww

DD

for the pairs of 2-1, 4-2,

3-1 and 4-1 frequency ratios are 1.897, 0.129, 0.968 and0.245 respectively. The intersection point of all the contoursindicate the position and extent of damage, which in thiscase works out to be 0.25 and 0.1 respectively (Fig. 2 (a) ).Figures 2 (b) shows the results of the remaining case. Afterthe geometric details of the damage are got, it is easy toextract the magnitude of damage. The least square esti-mation can be adopted, for this over-determined set of equa-

tions, (with four equations and one un-known), which in thiscase works out to be 0.10.

It is to be observed that, for symmetrical damages, the in-tersection point is also a point of zero slope and hence thecontours are tangential to each other. An extra frequencyinformation may be required to resolve this issue or addi-tionally, it is also proposed to have a static based systemidentification procedure, which shall resolve a symmetricand an un-symmetric damage, in conjunction with dynamicmeasurements.

Damage Estimation Through Deflection Measurements At

The Load Application Point


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A simplified formulation based on flexibility approach iswritten, using only deflection measurements and throughmonitoring of the change in deflection (ratio of change indisplacement to the original displacement). Certain condi-tions are also imposed such that the value of measureddeflection is more and hence the errors are less. These in-

clude Deflection is measured only at the loading point is used

in the inverse analysis.

Ratio of the change in deflection is used instead of the

absolute value of deflection.

Total strain energy (U) due to flexure can be summed up forvarious regions of the un-damaged Euler-Bernoulli beam(Fig. 3) as in the following expression

ò ò ò ò ò A B C D

ud

EI

dx M

EI

dx M

EI

dx M

EI

dx M

EI

dx M U

22222

22222

(2)

and ud are subscripts for damaged and un-damaged states.

Here 'α' ( 0 < α< 1)is the remaining ratio of EI after a dam-

age of 'β EI' has occurred

(1-α = β). The factor is termed as the modified dam-

age factor ( β* ) It is to be noted that the strain energy and

subsequently deflections are proportional to the modified

damage factor and not to the damage factor themselves.

Fig. 2 (a,b) Prediction of Damage Position and Extent from

Iso_Eigen_change Contours(a) D1, (b) D2

Fig. 3 Simply Supported Beam taken for Static SystemIdentification Studies

Reckoning 'x' from the right-hand side support and the

change of deflection is sought below the applied load it-

self, (5)

(6)

where is the incremental increase in deflection at the

'i-th' node due to a damage magnitude βj at the 'j-th' element.

(7)

If there are 'N' damage sites in the beam, the effect of all thedamages can be simply summed up and the above equa-tion can be written as,

(8)

For a particular case of a uniform and widespread reduc-tion in EI, the equation can be modified and the effects onboth the left and right sides of the load are added and theresulting expression is,

(9)

The above equation reinforces the well-known fact that fora uniform decrease in EI, throughout the beam, by a factorof α, deflection increases by a facor of 1/ α and change indeflection is ((1/ α)-1)

The ratio of increased deflection to the original deflection,


For the damaged beam, only the region of damage is re-

placed with anαEI.

(3)

This can be modified and written as,

ò òC C ud d EI

dx M

EI

dx M U U a22

22

ò+C

ud

EI

dx M U

2

12

aa

òC

ud

EI

dx M U

21

2

bb

òC

ud d

EI

dx M U U

21

2

bb (4)

Where, M = moment at any section, EI = flexural rigidity ; d

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for the same loading can similarly be written as,

(10)

In a system identification procedure, for deriving the sys-

tem parameters from the known values of ratio of changesin deflections from the original deflection values, aboveequation can be re-cast into a matrix form with un-known

vector composed of and known vector of ,

both related by a coefficient matrix depending on the ge-ometry of load position and damage. The matrix 'A', termedas the sensitivity matrix, is constructed relating the sensitiv-ity of damage at element 'j' to an increased deflection at

node 'i'. The vector 'b' is the un-known , modified

damage factor (β*) at various elements and vector 'c' is theknown change in deflection, expressed as the ratio of origi-nal deflection, occurring at node 'i' due to the effect of dam-

ages in all elements and which can be measured. Fig.4shows the results of the numerical study with simulated and

retrieved damages.

Conclusions

Iso_Eigen_value_Change contours constructed from

Cawley-Adams criteria are the effective means of iden-tification of damage in terms of damage position and

extent. It is possible to estimate the damage magnitude,as an over-determined problem, once the position andextents are known. These contours are more tolerant toerrors in measurements and up to 5% deviation, a re-gion of intersection is identified rather than a point andthe centre of the region is the likely damage location.

The method of damage identification from static mea-surements improve, if drive-point deflections are used(load and deflections at the same point), rotations de-rived from deflections are not used in the formulationsand more redundancy is incorporated in measurements.

Acknowledgement

The paper is published with the approval of Director,CSIR-SERC and his constant support and encouragementare gratefully acknowledged

Author Affiliation

Raghu Prasad. B.K, Professor, Indian Institute of Science,Bangalore, Lakshmanan. N, Scientist, CSIR-SERC,Chennai, Gopalakrishnan. N, Corresponding Author,Muthumani. K, Scientist, CSIR-SERC, Chennai

References

1. Caddemi, S and Morassi A, "Crack detection in elastic beams by

static measurements", Intl. Jl. of Solids and Structures, 44 (2007),

5301-5315.

2. Caddemi, S and Greco A, "The influence of instrumental errorson the static identification damage parameters for elastic beams",Computers and Structures, 84(2006), 1696-1708

3. Buda, G and Caddemi, S, "Identification of concentrated dam-ages in Euler-Bernoulli beams under static loads", Jl. of Engg.

Mech., ASCE, 133 (2007), 942-956.

4. Paola, M D and Bilello, C, "An integral equation for damageidentification of Euler-Bernoulli beams under static loads", Jl.of Engg. Mech., ASCE, 130 (2004), 225-234.

5. Choi, I Y, Lee, J S, Choi, E and Cho, H N, "Development ofElastic damage load theorem for damage detection in a stati-cally determinate beam", Computers and Structures, 82 (2004),2483-2492.

6. Choi, I Y, "Damage identification techniques for bridges usingstatic response", Ph. D thesis, Hanyang university, 2002.

7. Doebling S.W., Farrar C. R., Prime M. B., Shevitz, P. W., "Dam-age Identification. Health monitoring of structural and mechani-

cal systems from changes in their vibration characteristics - Aliterature review", Los Alamos National Laboratory, Los Alamos,New Mexico, (1996).

8. Hassiotis, S. and Jeong G.D., "Assessment of Structural dam-age from natural frequency measurements", Computers andStructures, 49, (1993), 679-691.

9. Hassiotis, S., "Identification of damage using natural frequen-cies and Markov parameters", Computers and Structures, 74,(2000), 365-373..

10. Li, Y Y, Cheng L, Yam L H and Wong W O, "Identification ofdamage locations for plate-like structures using damage sen-sitive indices: strain modal approach", Computers and Struc-tures, 80 (2002), 1881-1894.

11. Yam, L H, Li, Y Y and Wong W O, "Sensitivity studies of param-eters for damage detection of plate-like structures using staticand dynamic approaches", Engineering Structures, 24 (2002), 1465-1475.

12. Rus, G, Lee S. Y and Gallego R (2005), "Defect identification inlaminated composite structures by BEM from incomplete staticdata", Intl. Jl. of Solids and Structures, 42 (2005), 1743-1758

13. Rucka, M and Wilde, K, "Crack identification using waveletson experimental static deflection profile", Engineering Struc-tures, 28(2006), 279-288.

14. Nejad F.B, Rahai, A and Esfandiari a, "A structural damagedetection method using static noisy data", Engineering Struc-

tures, 27(2005), 1784-1793.

15. Vanlanduit, S, Parloo, E and Guilaume P, "Combined damagedetection technique", Journal of Sound and Vibration 266(2003), 815-831.

16. Yam L.H, Li Y.Y and Wong W.O, "Sensitivity studies of param-eters for damage detection of plate like structures using staticand dynamic approaches", Engineering structures, 24 (2002), 1465-1475

17. Wang X, Hu N, Fukunaga H and Yao Z H, "Structural damageidentification using static test data and changes in frequen-cies", Engineering structures, 23 (2001), 610-621.

18. Lakshmanan, N, Raghuprasad, B.K., Muthumani, K.,

Gopalakrishnan, N., and Basu D. (2007). "Wavelet analysis and


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enhanced damage indicators", Smart Structures and System- An Intnl Jl., 3, 23-49.

19. Lakshmanan, N, Raghuprasad, B.K., Muthumani, K.,Gopalakrishnan, N., and Basu D. (2008). "Damage evaluationthrough radial basis function network (RBFN) based artificialneural network scheme", Smart Structures and System- An IntnlJl., 4, 23-49.

20. Raghuprasad, B.K., Lakshmanan, N, Gopalakrishnan and N.,Muthumani, K. (2008), "Sensitivity of Eigen values to damageand its identification", Structural durability and health monitor-ing, 4(3), 117-144.

21. Lakshmanan, N, Raghuprasad, B.K., Muthumani, K.,

Fig. 4 Various Damage patterns for damage identification for a simply supported beam


Gopalakrishnan, N., and Basu D. (2009). "Identification of rein-forced concrete beam-like structures subjected to distributeddamage from experimental static measurements", Computersand Concrete- An Intnl Jl., 4 (1) .

22. Lakshmanan, N, Raghuprasad, B.K., Gopalakrishnan, N.,Sathishkumar, K., and Murthy S.G.N., Detection of contiguousand distributed damage through contours of equal frequencychange, Journal of sound and vibration (2010).

23. Raghuprasad, B.K., Lakshmanan, N, Muthumani, K. andGopalakrishnan N., "Enhancement of damage indicators inwavelet and curvature analysis", Sadhana, 31(4), (2006), 463-486.

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The Launch of the Journal of Structural Engineering World Congress

(SEWC) in 2011 at the time of the 4th SEWC is a major step in

recognizing the need for an international journal in this important area.

The journal will have its head office in Bangalore, a source of great

satisfaction in view of the many important contributions made in this

area by structural engineers working in India. I wish the journal and its

Editor-in-Chief Prof. B K Raghu Prasad the greatest success in this

venture.

1st March 2011

P. BALARAM

Message

P. BALARAMDirectorIndian Institute of ScienceBangalore - 560 012. India


INDIAN INSTITUTE OF SCIENCEBangalore - 560 012, India

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Message

The economic growth witnessed across all the developing countries has been instrumental in ever

increasing investments in infrastructure and on large projects intended to improve the quality of life ofthe human race. Due to this enormous increase in investments across the world, the area of Structural

Engineering has assumed significant importance. It is an area where the engineers world over had

responded with great innovations and is an area which will witness even more disruptive technologies

developing. Complex innovations cannot take place when confined to one region or a country and it

does not respect even barriers across disciplines. I am extremely happy to note that the Structural

Engineering World Congress (SEWC) has been very active in creating platforms such as International

Conferences to bring people together to share their knowledge, experience and best practices so that

the sharing of knowledge can contribute to its multiplication for the good of the humanity. I understand

that the World congress meetings in San Francisco, Yokohama and Bangalore have been extremely

successful. The 4th one planned to be held in Italy in April, 2011 is touted to be the largest and a

technically rich meeting.

The idea of launching an International Journal, on the occasion of the 4th Structural Engineering World

Congress meet by the SEWC is a very important step and is in the right direction of aligning the thought

leadership in this area towards global dissemination of knowledge and I am sure that this will grow the

area of Structural Engineering in a very impactful way.

On behalf of the Indian Institute of Science and on my own personal behalf, I wish to greet the SEWC

and those brilliant brains behind its activities and wish them all the very best in their efforts in furthering

the frontiers of research in Structural Engineering.

Sincerely yours,

N Balakrishnan

Prof. N. BalakrishnanAssociate DirectorProfessor, Supercomputer Education and Research CentreNational J C Bose Fellow

SERC/NBK/G17 March 2011


INDIAN INSTITUTE OF SCIENCEBangalore - 560 012, India

8/7/2019 Sewc eBook


Roland L SharpeFounding President SEWC, Inc. (1)

Art ic le

Structural Engineers

World Congress- Idea to Reality

Introduction

Structural engineering has been a

developing profession for more than

one hundred years. The first structural

engineering office in the western

United States (US) was opened in San

Francisco by H. J. Brunnier after the

1906 San Francisco earthquake.

Previously structural design of most

bu i ld ings was per fo rmed by

architectural offices.In some countries, universities do

not offer structural engineering “tracks”

but require architectural engineering

courses for building designers. Civil

engineers take different engineering

courses to become designers of

highways, bridges, marine structures,

dams, and so forth. In recognition of

the potential impact of structural and

civil engineering designs, there is a

growing trend in the U.S. and some

other countries to require a graduate

degree as a major qualifier for an

engineer to take an examination for

professional engineering license.

The societal impact of the structural

engineer (SE) is often quite broad. As a

result the SE may face major legal

liability should something go awry with

his design.

It became apparent in the 1980s

and early 1990s that the world was

becoming smaller due to moderntechnology and the economy was

becoming global as international trade

barriers were being removed by

agreements such as NAFTA, GATT,

European Union and pending

agreements in southeast Asia.

Financial interactions between

countries were being transacted on a

24-hour basis as new communication

technology became available. Major

companies from many countries were

expanding by building new plants or

acquiring existing companies in

countries with probable markets for

their products.

Architect-engineer companies

were being asked to design facilities in

many countries. Building codes,

bui lding mater ials, regulatory

procedures, permit requirements,

quality control, and processing varied

from nation to nation. Structural

engineers were being challenged toprovide required professional services.

Many international meetings were

being held on specific architectural

and structural engineering topics -

such as tall building design, bridge

design, ports and harbors, concrete

structures, steel buildings, Euro

standards, and so on. Few formal

discussions were held covering the

broader aspects of structural

engineering.

It was becoming apparent that SEs


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needed to look beyond local and

regional markets and learn from

counterparts in other countries. The

best way to accomplish this was to

meet and discuss face to face.

Informal discussions in the mid

1980s between U.S. and Japanese

structural engineers and researchers

raised questions about the role of the

st ructura l engineer , required

capabilities, and how the SE public

image could be improved. Further

in f o r ma l mee t ings and ma i lcorrespondence over several years

examined in some detail how this

i n t e r a c t i o n c o u l d b e s t b e

accomplished. These interactions led

to small meetings at American Society

of Civil Engineers

(ASCE) Congresses in the U.S.

which culminated in 1994 when six

professional organizations agreed to

form a coalition to sponsor and

organize the first Structural Engineers

World Congress (July 18 to 23, 1998) in

San Francisco.

Recognition of the need for a world-

wide SE Congress, need for interaction

between SEs worldwide, scope and

impact of SE services and effects onsociety, the need to improve the image

and credibility of the SE grew over the

next few years. The development of the

concept of a worldwide SE meeting, its

purpose, organizational structure, pos-

sible location, probable participants,

topics to be covered, and other appro-

priate issues are discussed in the fol-

lowing text.

Early Discussions

In 1980 the U.S. National ScienceFoundation (NSF) and Japan Building

Research Institute (BRI) initiated a joint

study involving full scale lateral load

testing of structural steel and

reinforced concrete structures. The

purpose of the study was to determine

if additional and/or modified reinforcing

of beam/column connections was

needed to improve the seismic

resistance of these types of structures;

in addition which type of computer

analysis could best predict the ultimate

resistance capacity of each type of

structure. Meetings were held mostly in

Tsukuba, Japan where the testing was

being performed at the BRI Test Facility.

Informal discussions held between

U.S. and Japanese structural engi-

neers and researchers

about structural engineers and

what their role should be were dis-

cussed. The initial result was conven-

ing of a joint U.S.- Japan Workshop in

1984 in Honolulu, Hawaii to discuss

structural practices in the two coun-

tries, the role of the structural engineer,

and how could the public image of the

SE be improved. After a successful

meeting it was unanimously agreed

that Workshop meetings should beheld every two years. The concept of a

broader scope SE meeting was infor-

mally discussed.

1991- 1992 - Comments and

suggestions were exchanged via

facsimile and telephone discussions

between the author and JSCA repre-

sentatives and other SEs in the U.S.

The American Society of Civil Engi-

neers (ASCE) and other professional

organizations convened annualmeetings where structural engineering

technical sessions were presented

covering the gamut of structural topics.

In the United States, the ASCE

Structural Division organized and

convened Annual Structural Engineer-

ing Congresses mostly attended by US

engineers. At these meetings small

groups of structural engineers would

meet, often in informal sessions, to

discuss topics of general interest to the

engineering profession. Attendees

represented professional organiza-

tions from various countries.

1993 - Informal discussions and

correspondence continued between

JSCA representatives, ASCE Structural

Division (STD) members, and others. In

April 1993 - at STD Annual Structures

Congress in Irvine, California - a

meeting was held of major U.S. SE

organizations plus others including

JSCA - to further discuss the need and

desirability of organizing a World

Structures Congress (WSC). As a

result of the discussions, the ASCE

STD established an Ad Hoc Committee

on World Structural Congress

Feasibility worldwide, scope and

impact of SE services and effects on

society, the need to improve the imageand credibility of the SE grew over the

next few years. The development of the

concept of a worldwide SE meeting, its

purpose, organizational structure,

p o s s i b l e l o c a t i o n , p r o b a b l e

participants, topics to be covered, and

other appropriate issues are discussed

in the following text composed of

representatives from American

Concrete Institute (ACI), International

Association of Bridge and Structural

Engineers (IABSE), National Council ofStructural Engineering Associations

(NCSEA) of U.S., Structural Engineers

Association of California (SEAOC) and

ASCE STD. The author was elected

Committee Chair. Japan Structural

Consultants Association (JSCA) was

invited to participate in the Committee.

In October, the committee was

elevated to an STD Task Committee

and in January 1994 met in San

Francisco to review input from parent

organizations, and develop preliminaryrecommendations.

Range of SE Activities

Although several international

organizations exist that serve structural

engineers needs in specific areas such

as bridges and buildings (IABCE), tall

buildings, earthquake engineering,

they do not serve many aspects of SE

concerns. A consensus developed in

the Task Committee that the WSC

should include the full range of SEissues - technical, professional, ethics,

education, legal, construction,

products, and other related issues.

There should be exhibits along with

sessions on these topics. It also

became apparent that the WSC should

be “people” oriented with the theme of

getting to know each other better. It

was estimated that there are about

50,000 structural engineers in the U.S.

and perhaps 200,000 or more in the

world.

The question of who is a structural

Structural Engineers World Congress - Idea to Reality


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engineer was examined. As noted

previously, in Japan civil engineers

design bridges and other structures

associated with infrastructure and

mostly work for the government. This

appears to be true for some other

countries. It was recommended that allengineers designing and constructing

structures are considered structural

engineers and should be included in

WSC. The Committee felt strongly that

the WSC should not become a

membership organization and should

not compete with existing international

SE organizations.

April 1994 - at the Annual ASCE

STD Congress in Atlanta, Georgia, the

Task Committee met and afterconsiderable discussion voted

unanimously to proceed with the

planning and organizing of a WSC.

ASCE stated that it did not want to be

the lead organization but believed that

a coalition of organizations should

manage the WSC, with sponsors

providing up-front funds to finance the

event. Co-sponsors would provide

some funding plus “in-kind” support.

JSCA pledged $15,000 in up-front

funds, ASCE and others said theyw o u l d c o n t a c t t h e i r p a r e n t

organizations for funding.

The group agreed that a separate

organization consisting of the coalition

members should be formed with the

specific purpose of organizing the

WSC. An Initial Steering Committee

( I S C ) w a s a p p o i n t e d f r o m

representatives of the six organizations

present at the meeting who agreed to

sponsor or cosponsor the WSC. The

author was elected as Committee

Chair.

1994 - In the ensuing months,

about 100 letters were sent to SE

and/or professional engineering

organizations in countries around the

world to determine their interest as a

participating, cosponsoring, or

sponsoring organization in a World

Structures Congress (WSC). Forty five

responses were received - twenty five

indicated interest as a sponsor,

c o s p o n s o r o r p a r t i c i p a t i n g

organization. Several others said they

would sponsor one or more technical

sessions. The Committee members

corresponded by mail, facsimile, and

telephone.

October 1994 - The ISC met in San

Francisco to formalize the organization

and start initial planning for the WSC.

Many important decisions were made:

1. Name changed to Structural Engi-

neers World Congress (SEWC).

SEWC to be incorporated as a non-

profit public interest corporation in

California. Six founders - ACI,

ASCE, IASS, JSCA, NCSEA, and

SEAOC.

2. Korean Society of Civil Engineers

was welcomed as a sponsoring

organization and a member of the

SEWC Board of Directors..

3. Officers were elected.

4. San Francisco was selected for the

first Congress to be held in 1998 -

date to be determined by

availability of a prime hotel.

5. Initial organization of Congress

planning effort - Steering, Program,Arrangements, Financial, Advisory

Committees and others were

established.

6. Directors were given various

assignments - to recommend

candidates for committee chairs,

possible funding sources, and

addit ional sponsors and/or

cosponsors.

1994-1998 Activit ies

A major change in organization wasmade by separating the Program Com-

mittee into two Committees - Technical

Program Committee; and Professional

& Practice Issues Committee. The

change was initiated because many

Structural meetings emphasize aca-

demic and research papers with lim-

ited presentations on practical prob-

lems associated with running an office,

establishing fees, professional liability,

marketing, and similar. A basic premise

of SEWC was that many issues faced

by the SE are non-technical yet are very

important to the progress and function-

ing of the SE profession.

A Call for Abstracts was issued and

mailed to over 1,000 professionals and

institutions. The Abstracts were

carefully reviewed by the respective

Program Committees. More than 900

abstracts were reviewed and a total of

723 papers were accepted and

presented at the Congress.

There were about 1800 participants

from 49 different countries. A large num-

ber of exhibitors presented their prod-

ucts. The 1998 SEWC was considered

a great success, many laudatory com-

ments were expressed by attendees.

JSCA promptly submitted an

application to sponsor the next SEWC

in Japan in 2002. The SEWC, Inc. BoD

approved their application and

authorized JSCA to proceed.

1998-2007 Activ ities

JSCA f o r med a sepa r a t e

corporation to manage SEWC2002. A

planning schedule was developed,

p r o j e c t b u d g e t e s t a b l i s h e d ,

committees appointed, and a

marketing group set up.

Solicitations were sent to major SE

organizations requesting sponsorship

and up-front funding.

The emphasis of the Congress was

focussed on addressing on an

internat ional basis the many

professional issues facing the

structural engineering profession.

There was considerable effort to

encourage presenta t ions on

professional issues including how

various countries are reacting to the

most recent trends affecting the

profession including advances in

modern technology, new social trends,

and professional changes.

SEWC 2002 was held in Yokohama,

Japan October 9-12, 2002. There were

1300 participants from 35 countries

and 384 papers from 27 countries.

Concerted efforts were made to help

participants interact at various social



8/7/2019 Sewc eBook


events. SEWC 2002 was a great

success.

SEWC 2007 was held in Bangalore,

India November 4-9, 2007. Over 1400

participants attended.

There was a substantial number ofexhibitors. The Congress was

excellent.

SEWC India organized and hosted

"Internat ional Col loquium on

Architecture-Structural Interaction

Bangalore April 22 to 25, 2010. The

organizers invited a number of

international engineers and architects

as keynote speakers - each of them

gave excellent presentations. There

were 900 engineers and architects plus200 students in attendance. An

excellent Colloquium.

Concluding Remarks

As noted earlier the structural

engineering profession is continually

expanding world wide.

The cultures and needs of the world

are ever changing. The SE profession

is intimately involved because of the

need for new industries, factories,

laboratories, infrastructure, and relatedfacilities. This expanding market for the

SE profession brings with it many new

issues facing the SE such as:

International Professional Licensing

Increased Educational Require-

ments

More Restrictive Regulatory

Requirements

Sustainability of StructuresLife Cycle Design and Cost

Business Ethics

Environmental Requirements

Legal Liability

New Materials and Their Long Term

Behavior Under Stress Improved

Collaboration with Architectural

Profession

Improved Quality Assurance

Better Understanding of RisksFrom Natural Hazards

Other issues will undoubtedly arise

as the future unfolds.

Acknowledgments

Many engineering colleagues havecontributed to the concept, convening,and success of SEWC 1998, SEWC2002, and SEWC 2007. I would like tocongratulate and thank each of you foryour selfless dedication and efforts to

improve the SE profession. Many ofyou put in long hours to help ensurethat each of the Congresses were asuccess.

I would especially like to acknowledge

the efforts and dedication of:

Dr. Katsumi Yano, JSCA Past

President

Professor N K Srivastava, Emeritus,

University of Moncton, NewBrunswick, Canada

Professor Alfredo H-S Ang,

Emeritus, University of California -

Irvine, California

Professor Gregory L. Fenves,

University of California, Berkeley,

California* Dr. Sundaram, President of SEWC,

Inc.

Dr. Ron Domer, Danville, California

A. Yamaki, Nikken Sekkei, Tokyo,Japan

I apologize for any name not

mentioned above - you have my

deepest thanks.

ASCE - Distinquished Member;

JSCA - Honorary Member

SEAOC - College of Fellows;

SEAONC - Honorary Member

EERI - Honorary Member; ACI - Life

MemberAssoc ia t ion o f Consu l t ing

Engineers India, Honorary FellowMember.



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few years ago while sitting at

my desk in walked a veryAconfident individual asking for

sometime and would I be interested in

designing a home for him and his

family. I was at that time mired in manyworks and responded “if you give me

complete freedom I might do it” to

which the response was, “agreed, but on

one condition I will review your design

and if not acceptable I may not go ahead”.

Deal accepted advance non refunda-

ble paid- and I had nothing to loose.

Preliminary investigations made

and said “when ready will call you and if

I come up with nothing you cannot ask

for the advance back”. “Done” andaccepting the challenge I took it upon

myself to see what I can come up with

nothing to loose. The list of

requirements was long a whole

integrated joint family to be resettled

from a small urban apartment into a

whole new environment.

I set pencil and crayon to paper

and every spare time was spent on

this sketch. I only used only one thick

sheet and on it superimposed sketch

over sketch emphasizing the

decisions with color and charcoal.

Weeks passed, I thought he would call

and say “time up”. But not a whimper,

almost a month later when I thought I

had spent enough time “come over”

and he did within the hour.

ONE LOOK “I have never seen any-

thing like this- and I must say I have

been to many architects but this is well”

with that he took the drawing saying “will

get back if We accept it” the way he reac-

ted I thought it would be the last of him.

Ten minutes later he was back

gave me one hard look and said “can

you really build this and I have a view of

how it might look”. I replied “as of now I

don't know but I shall and I never give

views of my projects and that was a

pre-condition” In his very individualistic

REMINISCENCES - Sankalp-An architectural adventure story

Art ic le

Prof. Jaisim KJaisim Fountainhead, Bangalore


8/7/2019 Sewc eBook


REMENISENSES - Sankalp - An architectural adventure story

he agreed and asked “how much it

would cost”. I replied “I do not know”

And in passing I added “ it can only

be built by a builder I trust and have

confidence in”

And the real story of realizationbegan It dawned on me after he left Oh

boy, what have I got into this

extraordinary organic form with flowing

walls and interplaying spaces moving

into smoothly rising levels. I had never

done anything like this before, I was

sure he would take the drawing and

run. Here was something more than a

challenge- this was DO or DIE.

Called JACK Srinivas (the builder)

“think we can do it” “Sir, you put yourmind and it is done” was the confident

reply. And to add fuel to the fire we

decided to go all the way and see how

much we could stretch ourselves.

Country bricks and that too used

vertically to get the soft curves and

heights, was the main material and so

kilns were and hunted and orders placed.

Now, the site smiled mischievously

and added its own challenge, there

was a reservoir nearby and arrogantlywe set the base of the building lower

than the water table, and seepage and

dampness became a big issue along

with the black cotton soil. We rose to

the challenge no normal foundations

A big pad of rocks as large as the

house and wider was laid in layers and

rollers used to compact them. Over this

a concrete base cum floor was

integrated something like aerodrome

runway. If planes weighing several

tones can land with immense force why

not some dumb walls stand!. But the

walls loved it and began to sing. And as

we rose with them we took their

performance to greater heights by

making them move outwards defying

every logic in their sensual movement

which finally got crowned by the vast

brick dome. Amazing is what came to

be realized. Little did we comprehendthe extent of the achievement?

We were all in such a mood that

every movement was orchestrated with

all sorts of inputs as long as there was

some value in them. From the humble

laborer to the Maistrys to every other

worker would with a smile come up with

their inputs and innovations to make

this a real master piece. This clearly

expressedthehiddentalentthatmany

forgotten humans have in their daily

chores.

Wewerelikechildrenintheirplay

den,timewasforgotten.Itwentonand

ontheadventureneverseemedtoend

andIdonotseeitendingeventoday.

That Home beckons me like a siren

askingformoreandmoreindulgence.

Thelighting ofthedomeismastered

withclaypotsthatdefinethetimeofthe

year, like a Sun calendar. Theresonance that this space affords is

magicalifImaysayso.Itisamystifying

atmosphereeverynookandcornerhas

a little story within the larger story.

Sankalp is an epic, it cannot be

described easily with words, and it

mustbelivedandfelt.Ittakesabuseas

easilyaspraise.

Icangoandon,FromtheGarage

to the service quarters and the

gardens it is one experience. Yes,eventhegarage-mustbeseentobe

believed. BUT Sankalp is a very

mischievousliving being,itdoesnot

like being neglected or left alone, it

demands attention like all intelligent

childrendo.ITisnot justaHome,itis

partofone'slife.

Awaiting Sankalp's next call I will

signoff!

Jaisim

www. jaisim-fountainhead.com


8/7/2019 Sewc eBook


o meet the growing demands of

the city a new, modern green

field airport was planned atTShamshabad on the outskirts of the

city. The project is the first privatelydeveloped airport in India, a consor-

tium led by GMR, comprises of the

Airport Authority of India and Malaysian

Airports Authority. The new airport is

designed to handle 12 million passen-

gers per annum initially and will in its final

stages be expanded to 40 million pas-

senger per annum ultimate capacity.The Passenger Terminal Building

(PTB) design is based on a centralprocessor linked with two linear piers,

serving 10 contact stands in Phase 1

but extendable to accommodate 32

contact stands in its final phase. A high

level of operational flexibility has been

built in to meet the park demands for

domestic and international operations

through Swing Gates. The PTB is

des igned to meet the la test

international standards by ICAO / IATA,including the full segregation of

departure and arrival flows, short

unassisted walking distances, 60

minutes Minimum Connecting Time,

boarding bridges that can serve

Art ic le


Hyderabad International Airport

Passenger Terminal Building- Project Description

Winston Teng ShuPrincipal, Integrated Design Associates Ltd., Hong Kong

8/7/2019 Sewc eBook


aircrafts from code C to code F, in line

5-levels security screening for all hold

baggage, and the provisions for a fully-

automated baggage handling system.

The rationalized design proposes

an alternative organization of major

functions, space utilization, structural

grids and service systems within the

PTB to the given Masterplan. The

alternative new design created a PTB

that is highly modularized and

repetitive to ease construction;

eliminated a 10m deep basement to

shorten the construction schedule;

reduced the overall construction area

by 8.5% to save cost while the revenue

generating areas have been increased

by 12.7% to improve investmentreturns. The alternative design was

commissioned in September 2005 and

the 105,000m2 PTB and the Air Traffic

Control Complex are scheduled to

complete in a record time of 30 months

from the date.

The architectural design of the PTB

has a lofty and flowing roof form,

spanning from the Airport Village by

means of a fabric structure, it reaches

the peak over the Check in Hall and

finally lowers down to shield the façade

from solar heat along the 1.2km length

piers on the airside. The flowing roof

gives a strong direction to the


departure passenger flows, and

through the skylights with the floating,

iconic “Temple Leaf” reflectors hung

below them, the entire PTB departure

level is totally lit by natural light during

the day and by diffused up lights in the

night.

The 2.5 year's period from design

inception to operation means an

extremely tight program for a project of

this scale. To ensure on-time

completion of the design to meet the

stringent procurements program by all

disciplines, the work was packaged

systematic ally t o allow timely

exchange of design information in a

progressively structured manner. The

pro ject'stightbudgetconstraintsalso

demanded a high degree of cost

effectiveness analysis throughout the

design process, including capital

costs, life cycle costs, developing

alternatives, etc. The close co-operation between the various

d isc i p l i nes req ui red a st ro ng

managementofteamwork,andinthe

12 months of detail design the team

producedover3500detaildrawingsfor

construction.Thenewairportandthe

PTBhasopenedon14March2008by

Mrs. Sonia Gandhi and it begins

operationalintheweekfollowing.The

PTB has become an architectural

landmark for it is the first ma jor

infrastructure public building of thisscale being commissioned in the

moderneraIndia.

In recognition of excellence in its

design and services provided to the

travelling public, the Hyderabad

InternationalAirporthasbeenawarded

one of the Top Five Best Airports

Worldwide,andtheBestAirportbysize

in the 5 15 mppa category by the

Airports council International of

Genevain2009.

Hyderabad International Airport Passenger Terminal Building - Project Description

8/7/2019 Sewc eBook


News

Incredible but True - 15 - StoreyedHotel Built in Less than 6 Days

The pace, at which China has under-taken seemingly impossible con-

struction tasks, has been impressiveover the years. The country is nowperhaps home to more mega struc-tures than anywhere else in theworld. But another recent project,takes the cake, for not being the big-gest project, but for the speed atwhich this particular building wasbuilt. A 15 storeyed hotel was built in6 days flat. Now, that is somethingincredible.

The building, which epitomizes theprowess of the country's construc-tion engineers, is located inChangsha, Hunan province. Thecompany behind the building hasbeen China's Broad Group. The com-pany pitched all its might and cameout with this astounding achieve-ment by constructing the 15-storeyed Ark Hotel in less than sixdays time.

Meticulous planning was behind the

rapid pace at which the constructionwork took place. A team of around200 workers worked in perfect tan-dem to achieve the feat. The struc-tural framework of the building waserected in just 46.5 hours. The exter-nal cladding and internal non-structural surfaces were completedin a matter of just 90 hours, making itone of the most remarkable feats ofconstruction ever attempted.

The building has been designed towithstand a 9.0 magnitude earth-quake too. Not only this, the hotel

used just one sixth of the material ofan equivalent sized building with acost saving of around 20 percent.The designers have also incorpo-rated several energy efficient fea-tures in the building to make it fivetimes more energy efficient thanother comparable buildings. Someof the features include, 6 inches ofthermal insulation, LED lighting sys-tems, external solar shades and tri-ple pane windows. There are reportsthat the company intends to con-struct 15 other similar buildings else-where in China and 30 in other partsof the world.

It must be noted here that the below-

ground construction and foundationwere completed before the count-down was started. The building alsouses several prefabricated compo-nents, which is essential for settingsuch scorching pace. Even whenthese caveats are taken intoaccount, the construction of thebuilding is a remarkable story thatshowcases the rapid strides that theconstruction industry has made in China.

This is not the first time that the

Broad Group has been in news. Thecompany had earlier completed theconstruction of a fairly complexpavilion in the Shanghai World Expoin just one day flat. Apart from thespeed of construction, the Ark Hotelalso brings into attention the fact thatsustainable building technology canbe incorporated in such structures.The building is also a symbol of thebuilding waste minimization, as theworld looks towards a greener future.

Cute Bubble Tentscould be perfect f or

Living in the Wild

Cute little Bubble Tents could be the

perfect answer to staying in jungles,

as man once used to do earlier.

These bubble tents have been

launched by a company named

Bubbletree and have become a hit

with those looking to enjoy wilder-

ness in its entire splendor.

Panama CanalAlternative beingplanned by China

China is now reportedly in talks with

the government of Columbia for theconstruction of a 220 km rail link that

will join the latter's Atlantic and Pacific

Coasts.The link would involve han-

dling cargo containers, with the link

transporting them in a much more

quicker time, in a cost effective man-

ner across the two coasts. This link , if

complete, could pose a real threat to

the Panama Canal.

Colombian president Juan Manuel

Santos is reported to have said "It's areal proposal. It is quite advanced. I

don't want to create exaggerated

expectations, but it makes a lot of

sense." The proposal is now being

eagerly watched by several leading

countries around the world.

Rough estimates put the cost of the

project at about US $7.5 billion.

Critics of the proposal however feel

that the project is not required with

the successful expansion of the canal,which has doubled its capacity, allow-

ing for the passage of large ships.


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The globe-shaped prefabricated

dwelling is available in half-transpa-

rent or fully transparent designs. The

manufacturers have also come out with

several different models of the bubble

tents to suit different requirements.

The bubble tents come complete

with sofas; roll out beds and portable

wardrobes. The manufacturers havealso made provisions for customiz-

ing the bubble tents to be tree sus-

pended versions.

London is already home to some

of the most exotic luxury hotels in

the world. You can now add one

more to the list in the form of a five

star hotel that will be, believe it or

not, completely underground.

The new hotel, designed by

Reardon Smith Architects, would

be located at the Hersham Golf

Club in Surrey, London. The hotel

will have 200 plus guestrooms, all

underground, making it one of the

most unique hotels in the world.

The entire area would be covered

with a lush green garden that

would blend seamlessly with the

natural beauty of the surrounding

country side.

A Luxury Hotel that wil lbe Completely Underground

Frank Gehry's New Iconic Skyscraper in New York

World renowned architect Frank

Gehry's new iconic skyscraper

opened in New York amidst much fan-

fare recently.

The building has been the talk of the

town and has created a buzz in the

engineering and architect commu-

nity. The 76-storeyed building named

“New York by Gehry” has laid claims

to being the tallest residential tower in

the western region.

Some critics in the city have called

the building “the best skyscraper

since the 1960s” in New York. The

building is also said to be on the vergeof going in for green certification.

News

Ancient Church nowbecomes a

Modern Bookstore

An ancient Dominican Church has

been transformed into a spectacular

modern book store, thanks to the cre-

ative genius of architecture. The

Church which dates back to the 13th

Century has been briefly used as aparish, before it was converted into a

warehouse and then into a giant park-

ing lot. It was converted into its pres-

ent form by architecture firm Merkx

and Girod.

There is a special viewing gallery at

the back of the structure from where

visitors can admire the spectacular

14th century ceiling frescoes or relax

over a cup of coffee at the café that is

located in place of the former choir.


8/7/2019 Sewc eBook



News

Landmark tower Resembling Chinese Lantern

Guosen Towers a new landmark towerslated for Shenzhen, China resem-bles a giant Chinese lantern, the 204meter tall tower will feature shadinglouvers on every floor, rainwater recy-cling, and natural day -lighting foreach employee's work station.

The volume of the tower has a squarefloor plan with an elegant, slender vol-ume that allows daylight to reach intothe building to provide a more plea-surable working environment for

employees. So that each worker hasaccess to views and natural daylight,no workspace was placed furtherthan 11 meters away from the facade.The edge of each floor was angleddown 35-55 degrees to create ashade for the floor below and largeglass fronts connect these louverstogether. Each louver's size and anglewas optimized for its location on thebuilding and relationship to the sun.For example, on the north side, the lou-

vers are smaller than on the south side.

The louvers can also accommodatesolar panels to generate electricity,

and they reduce the overall coolingload by 33%. Rainwater is collectedoff the louvers and piped into the greywater circulation for use inside thebuilding. Plus a lengthy water pipe sys-tem runs invisibly through the façadecollecting heat from the sun, and thesolar cells heat up water. Employeesand visitors also have quick and easyaccess via an underground tunnel tothe nearby metro station.

Parts of the facade are lifted to create

a double height ceiling for a more dra-matic effect and better views of thecity. These two double height featuresin the middle of the tower aredesigned as small amphitheatre withterraced seating that can be used forconferences and gatherings. A lowrise building next to the tower holds ashopping and conference center. Theend result of the louvered towerresembles a giant Chinese lantern,which will provide a warm glow to thecity at night.

Ult ima Tower A 2-mile high Mt Doom-Esque Structure

Architect Eugene Tsui is taking thegigantic volcano tower concept to awhole new eco level, by taking designinspiration from the natural world. Hisnew design for the Ultima Tower a 2-mile high Mt Doom-esque structureborrows design principles from treesand other living system to reduce itsenergy footprint. Tsui's concept forthis towering, ultra-dense urbandevelopment has certainly capturedthe attention with its thought-provoking design.

The Ultima Tower is an innovativegreen design concept proposed toresourcefully use earth's surface andallow sustainable distribution ofresources within a dense urbansetting. Designed to withstand

natural calamities, Ultima Tower is

highly stable and aerodynamic.Rather than spreading horizontallythe structure rises vertically from abase with a 7,000 foot diameterinspired in part by the termite's neststructures of Africa, the higheststructure created by any livingorganism.

Surrounded on all sides by a lake, thebuilding would use building inte-grated photo-voltaic solar cells tomeet most of the electrical energyrequirements. The tower would alsouse Atmospheric Energy Conversionto exploit the differences in atmo-spheric pressure at the bottom andtop of the tower and convert this differ-ential into electrical power. Wind tur-bine energy would also be used to

power the tower.

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Events

In 2011, MesseMünchen International (MMI), a

leading organizer of global trade fairs will be

launching the successful ConBuild trade fair

concept in Southeast Asia's biggest economy

and high growth market of Indonesia.

Under MMI's INFRASTRUCTURE initiative to

suppor t and promote in f rast ructure

development through top class international

trade fairs and conferences, ConBuild extends

this initiative to the Construction and Building

sector the foremost sector in infrastructure

development.

Details

Dates: 13th April 2011 16th April 2011

Contact Point: Ms. Denise Jones

Tele: + 65 6236 0988

Fax: + 65 6236 1966

Email: [email protected]: http://www.conbuild-indonesia.com/homepage.html

Location: Jakarta, Indonesia

ConBui ld 2011 Indones ia

The 6th Edition of the annual exhibition for the

Construction industry in the Northern

Gulf,gulfBID is the event that brings leading

suppliers, brands, equipment and services face-

to-face with clients and buyers with an aim of

inspiring more deals and implementation of the

latest trends and ideas.

Details

Dates:26th April 28th April 2011

Contact Point: Hilal Conferences and Exhibitions

Tele: + 973 17 299123

Fax: + 973 17 299155

Email: [email protected]

Website: www.gulfbidexhibition.com

Location: Hall 1, Bahrain InternationalExhibition and Convention Centre

gulfBID 2011 - Bahra in

In its 8th consecutive year, Project Qatar 2011 is

one of the region's leading construction events.

This highly anticipated show has become an

annual networking event for companies and

individuals operating across all construction

sectors. A perfect platform for high-caliber

investment deals, an ideal showcase for the

latest cutting-edge construction machinery,

equipment, systems and material, Project Qatar

provides a unique opportunity to conduct

business and gain access to a competitive

market with the industry's top companies and

professional visitors in one convenient location.

Details

Dates: 2nd May 5th May 2011

Contact Point: IFP Qatar Ltd.

Tele: + 974-4-329900

Fax: + 974-4-432891


Website: http://www.projectqatar.com/

Location: Doha, Qatar

Projec t Qatar 2011

Construmat is synonymous with construction

materials. It's the trade show that brings together

the whole sector. The Show is a benchmark in

Europe and is a recognized platform that offers

the best opportunities for expansion.

Details

Dates: 16th May 21st May 2011Contact Point: Fira Barcelona

Tele: 902 233 200

Fax: 93 233 21 98

Email: info(at)firabcn.esconstrumat@firabcn .es

Website:www.construmat.com

Location: Barcelona, Spain

Const ruma t 2011 - Spain


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Since its foundation in 2000, the CTT has rapidly

developed into the most important trade fair for

construction equipment and technology in

Russia and the CIS. Its concept offers

international machinery and equipment

manufacturers the opportunity of entering the

markets of Russia and the CIS and of

surrounding regions.

Details

Dates: 31st March 4th April 2011

Contact Point: IMAG Internationaler Messe-und

Ausstellungsdienst GmbH / Medial Global

International GroupTele: 089-94922-0 / + 7-495-2035300

Fax: 089-94922-350 / + 7-495-2034100

Email: [email protected] / [email protected]

Website: www.ctt-moscow.com

Location: Moscow, Russia

CTT Moscow 2011

The objective of MADE expo is to satisfy a

precise market requirement, to overcome the

lack in Italy of an important world-class

showcase. Made expo strives to guarantee

productive excellence in terms of the technology

and design of Italian business and provide an

exhibition setting able to capture international

attention.

Details

Dates: 5th October 8th October 2011

Contact Point: MADE eventisrl

Tele: + 39 02 80604440

Fax: + 39 02 80604397

Email:[email protected]

Website: www.madeexpo.it/en/index.php

Location: Fiera Milano

MADEexpo 20 11 - I ta ly

Concret e Show 2011 - Brazi l

CONSTRU India is designed as the perfect

platform to introduce new technologies. Backedby our direct contact with the industry, we intend

to bring together buyers and sellers enabling

scope of a perfect presentation.Constru

Indiafocuses on six major segments. Viz. Urban

Infrastructure & Transportation, Green &

Intelligent Buildings, Build with Steel,

Construct ion Engineer ing & Design,

Construction & Building Materials, Electricals in

Building & Construction.

Details

Dates: November 2011

Contact Point: India-Tech Foundation / Winmark

Services Pvt. Ltd.

Tele: + 91-22-2648-4901 / + 91-22-2660-5550

Fax: + 91-22-2260-3992 / + 91-22-2660-3992

Email: [email protected] / [email protected]

Website:www.winmark.co.in

Location: Mumbai, India

Const ru Ind ia 2011

Events

Concrete Show South America 2011is the

largest international event for technology in

highway, building and infrastructure specifically

in Latin America. It will serve as an international

meeting point for business and technological

users of concrete and their users.

Details

Dates: 31st August 2nd September 2011

Contact Point: UBM Sienna, André

Sanches(Event Manager)

Tele: + 55 11 46891935

Fax: + 55 11 46891926


Website: www.concreteshow.com.br

Location: São Paulo, Brazil


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8/7/2019 Sewc eBook



he 5th Structural Engineers World Congress (SEWC), which is dedicated to the art, science, and practice of structuralengineering, is slated to be held in Singapore in 2015.The event holds special significance as it marks an occasion where theT

conference is being held in a city, which is renowned for its prowess in structural engineering and its iconic buildings. The eventwould be conducted by the Association of Consulting Engineers, Singapore (ACES) and the Prestressed and Precast ConcreteSociety of Singapore (PPCS).

The World Congress held every four years, aims to cover major aspects pertaining to technical, and professional practice

issues. The congress focuses on the needs and the contemporary issues of the structural engineering profession worldwide andhighlights the profession's interface with the society. It also re-iterates the impact of the structural engineering profession on thesociety reflected by excellent public image, standing, and credibility of structural engineers. SEWC 2015 presents exce llentopportunities for structural engineering professionals to interact with each other and to learn more about what is happening in theWorld of Structural Engineering.

STRUCTURALENGINEERSWORLDCONGRESS 2015

- SINGAPORE

The City of Iconic Structures Beckons Structural Engineers

SEWC 2015

Jointly Organized by

ACESPrestressed andPrecast Society

Supported By

BCA SECB

8/7/2019 Sewc eBook


Ramasamy


8/7/2019 Sewc eBook



sewc ebook

Documents