earthquake resistant design of reinforced concrete buildings by otani (1)

8/9/2019 Earthquake Resistant Design of Reinforced Concrete Buildings by Otani (1)

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Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, February 2004 Co!yr"ght # 2004 Ja!an Concrete $n%t"tute 3

Invited Paper

Earthquake Resistant Design of Reinforced Concrete Buildings&a%t and FutureShunsuke Otani 1

'ece"ved ( )e!te*ber 2003, rev"%ed 2+ Nove*ber 2003

AbstractThis paper briefly reviews the development of earthquake resistant design of buildings. Measurement of ground accel-eration started in the 19 !s" and response calculation was made possible in the 19#!s. $esign response spectra wereformulated in the late 19%!s to 19&!s. 'on-linear response was introduced in seismic design in the 19&!s and the capac-ity design concept was generally introduced in the 19(!s for collapse safety. The damage statistics of reinforced con-crete buildings in the 199% )obe disaster demonstrated the improvement of building performance with the developmentof design methodology. *uildings designed and constructed using out-dated methodology should be upgraded. +er-formance-based engineering should be emphasi,ed" especially for the protection of building functions following fre-quent earthquakes.

1. Introduction

n earthquake" caused by a fault movement on the earthsurface" results in severe ground shaking leading to thedamage a n d c o l l a p s e o f b u i l d i n g s a n d c i v i l -infra-structures" landslides in the case of loose slopes"and liquefaction of sandy soil. f an earthquake occursunder the sea" the associated water movement causeshigh tidal waves called tsunamis.

/arthquake disasters are not limited to structuraldamage and in0ury death of people under collapsedstructures. 2ire is known to increase the e3tent of thedisaster immediately after an earthquake. The breakageof water lines reduces fire fighting capability in urbanareas. The affected people need support" such as medi-cal treatment" food" clean water" accommodations andclothing. 4ontinued service of lifeline systems" such aselectricity" city gas" city water" communication lines andtransportation" is essential for the life of affected people.$amage to highway viaducts or railway" as seen in the199% )obe earthquake disaster" can delay evacuationand rescue operations. t is the responsibility of civil and building engineers to provide society with the technol-ogy to build safe environments.

5einforced concrete has been used for building con-struction since the middle of the 19th century" first for some parts of buildings" and then for the entire buildingstructure. 5einforced concrete is a ma0or constructionmaterial for civil infrastructure in current society. 4on-struction has always preceded the development of structural design methodology. $ramatic collapse of buildings has been observed after each disastrousearthquake" resulting in loss of life. 6arious types of

1

+rofessor" $epartment of $esign and -rchitecture"2aculty of /ngineering" 4hiba 7niversity" 8apan. E-mail: %hun%u e.otan" faculty.ch"ba-u. !

damage have been identified through the investigationof damages. /ach damage case has provided importantinformation regarding the improvement of design andconstruction practices and attention has been directed tothe prevention of structural collapse to protect the oc-cupants of building in the last century.

Thank to the efforts of many pioneering researchersand engineers" the state of the art in earthquake resistantdesign and construction can reduce the life threat inreinforced concrete buildings. ttention should be di-rected to the protection of e3isting structures con-structed using old technology. The vulnerability of thesee3isting structures should be e3amined and seismicallydeficient structures should be retrofitted. One of theimportant research targets in present earthquake engi-neering is the development of design methodology tomaintain building functions after infrequent earthquakes"for e3ample" through the application of structural con-trol technology.This paper reviews the development of earthquake en-gineering in relation to earthquake resistance of build-ings and discusses the current problems in earthquakeengineering related to reinforced concrete construction.

2. Develop ent of seis olog! andgeoph!sics

/arthquake phenomena must have attracted the curiosityof scientists in the past. ncient reek sophists hy- pothesi,ed different causes for earthquakes. ristotle: ; - s theory was believedthrough the Middle ges in /urope. The 1(%% ?isbon/arthquake :M;.(=" which killed (!"!!!" partially due toa tsunami tidal wave" and a series of earthquakes in

" ). /tan" Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, 2004


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?ondon in 1(#9 and 1(%! attracted the interest of scien-tists.

The first scientific investigation about earthquake phenomena is believed to have been carried out by5obert Mallet" who initiated the physico-mechanicalinvestigation

of

earthquake

wave

propagation.

@e

in-vestigated the earthquake phenomena of the 1;%( 'aples /arthquake" and used such technical terms as

Aseismology"B Ahypocenter"B Aisoseismal"B and Awave pathB in his report :Mallet" 1;&s work on seismology and /wing noted the differ-ence between primary and secondary waves in the re-corded ground motion.

The 7niversity of Tokyo was renamed as the mperial7niversity in 1;;&. )iyokage Sekiya" who workedclosely with /wing and Milne" became the first profes-sor of seismology chair at the 2aculty of Science.2usakichi Omori who succeeded him in 1;9(" was ac-tive in e3perimental as well as theoretical research for earthquake disaster mitigation.

The relation between fault movements and earth-quakes was pointed out by rove ). ilbert" a 7.S. ge-ologist" who reported in 1;(< that earthquakes usuallycentered around a fault line. 4lear relative movementwas observed across the San ndreas 2ault after the19!& San 2rancisco /arthquake :Ms ;. =. This earth-quake caused (!! to ;!! deaths and destroyed s continental drift. +late tectonics can describethe accumulation of strains at the boundaries of ad0acent plates or within a plate due to plate movements at theearthFs surface" which cause earthquakes.

Ma0or earthquakes occur along the boundary of mov-ing tectonic plates when the strain energy" accumulated by the resistance against inter-plate movement" is sud-denly released. This type of inter-plate earthquakes oc-curs repeatedly at a relatively short interval of %! to

years. Seismically blank regions" where seismic activityis quiet for some time along the tectonic plate boundary"are identified as the location of future earthquake oc-currences. @owever" it is not possible at this stage toaccurately predict the time" location and magnitude of earthquake occurrences.

nother type of earthquakes occurs within a tectonic plate when the stress accumulated within a plate by the pressure of peripheral plate movements" e3ceeds theresisting capacity of the rock layers at the fault. Theepicenter is relatively shallow within ! km from theearth surface. The fault in a plate remains as a weak spotafter an earthquake" and earthquakes occur repeatedly at

the same location if stress accumulates up to the failurelevel. The location of many active faults has been iden-tified by geologists" and is taken into consideration indeveloping a seismicity map for structural design. f anintra-plate earthquake occurs near a city" the disaster indensely populated areas can be significant. t should benoted that this type of intra-plate earthquakes occurs at along interval of 1"!!! to "!!! years. Therefore" it ismore difficult to accurately predict the time" locationand magnitude of intra-plate earthquakes.

Ee need to emphasi,e the need for disaster mitigationmeasures in society focusing on optimum use of seis-mology and geophysics data.

). /tan" Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, 2004 #

3. Da$n of earthquake engineering


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t should be noted that Sir saac 'ewton" in 1&;( pro- C

posed the law of motion in A+hilosophia 'aturalis +rin-cipia MathematicaBD i.e." when a force acts on a particle"the resultant acceleration of the particle is directly proportional to the force. The equation was introduced to

m

mg

calculate the motion of stars in the universe. The law of motion was introduced in engineering by 8. 5. h < b <d> lembert who proposed the so-called $> lembert>s principle in his ATraitG de $ynamiqueB in 1(# D i.e." theequilibrium of forces can be discussed in a dynamic problem by introducing a fictitious inertia force" propor-tional to the acceleration and mass of a particle but act-ing in the direction opposite to the acceleration.

8ohn Eilliam Strut" also known as ?ord 5ayleigh" inhis ATheory of SoundB published in 1;((" discussed thevibration of a single-degree-of-freedom system withviscous damping under harmonic e3citation" longitudi-nal" torsional and lateral vibration of bars" and the vibra-tion of membranes" plates and shells. Such knowledgecould not be used in earthquake engineering for manyyears because the ground acceleration signal of anearthquake was not measured and because the equationof motion could not be solved for an arbitrary e3citationfunction.

3.1 Intensit! of ground otion/arly earthquake engineers and seismologists must haveknown the importance of ground acceleration to esti-mate inertia forces acting on structures during an earth-

quake. The seismograph" however" was not capable of measuring ground acceleration" which was more impor-tant for engineering purposes. /. S. @olden :1;;;=" $i-rector of the ?ick Observatory in 4alifornia" reportedthat AThe researches of the 8apanese seismologists haveabundantly shown that the destruction of buildings" etc."is proportional to the acceleration produced by theearthquake shock itself in a mass connected with theearth>s surface.B

ndeed in 8apan" efforts were made to estimate thema3imum ground acceleration during an earthquake.8ohn Milne and his student" )iyokage Sekiya" estimatedma3imum ground acceleration amplitudes from themeasured seismograph :displacement= records by as-suming harmonic motions in 1;;#. *ecause the domi-nant frequencies in displacement and acceleration sig-nals were different" this method tended to underestimatethe ma3imum acceleration. Milne :1;;%= introduced theEest>s equation" which was used to estimate ma3imumground acceleration necessary to overturn a rigid body of width b and height h attached on the groundsimply using dynamic equilibrium :Fig. 1=D

b

h

where acceleration is e3pressed as the ratio togravitational acceleration. This method was e3tensively

A round Accelerat"on F"g. 1 The e%t % e5uat"on.

used in 8apan to estimate the intensity of ground mo-tions from the dimensions of overturned tomb stonesafter an earthquake.

The

1;91 'ohbi

/arthquake

:M

;.!=

caused

signifi-cant damage to then modern brick and masonry struc-

tures in 'agoya 4ity. This is a largest-class near-fieldearthquake to have occurred in 8apan. ("


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design. @e assumed a building to be rigid and directlyconnected to the ground surface" and suggested a seis-mic coefficient equal to the ma3imum ground accelera-tion normali,ed to gravity acceleration . lthough henoted that lateral acceleration response might be ampli-

fied from

the

ground

acceleration

with

lateral

deforma-tion of the structure" he ignored the effect in determin-

ing the seismic coefficient. @e estimated the ma3imumground acceleration in the @on0o and 2ukagawa areason alluvial soft soil in Tokyo to be !. ! and above onthe basis of the damage to houses in the 1;%% nsei-/do:Tokyo= /arthquake" and that in the Camanote area ondiluvial hard soil to be !.1% . Sano also discussedearthquake damage to brick masonry" steel" reinforcedconcrete and timber houses and buildings and proposedmethods to improve the earthquake resistance of suchstructures.

3.3 %tructural anal!sis ethods*uilding structures are highly statically indeterminate.

ctions and stresses in a building must be calculated before seismic forces can be utili,ed in design. 2unda-mental studies of structures were developed in the mid-dle of the nineteenth century. 8. 4. Ma3well in 1; andO. Mohr in 1;(# separately developed the unit loadmethod to determine the deflection of elastic trusses andthe fle3ibility method to determine redundant forces instatically indeterminate trusses. ?. M. @. 'avier was thefirst to use the stiffness method of analysis in the prob-lem of two-degree-of-kinematic indeterminacy in 1;s theorems were presented

in 1;(9.The application of the stiffness method and the slopedeflection method to plane frames originated with .*endi3en in 191#" and was also used by E. Eilson and. . Maney in 191%. set of linear equations had to be

solved before the moment distribution could be deter-mined. The practical method of structural analysis wasintroduced laterD the moment-distribution method was presented by @ardy 4ross :19 !=.

Tachu :Tanaka= 'aito at Easeda 7niversity intro-duced the slope-deflection method in 8apan in 19

'aito>s $-value method of structural calculation for

frame buildings was further e3tended by ). Muto at themperial 7niversity of Tokyo : rchitectural nstitute of

8apan" 19 =. ?ateral stiffness of columns was theoreti-cally evaluated taking into account :a= fle3ural stiffnessof the column" :b= stiffness of ad0acent girders immedi-

ately above

and

below

the

column"

and

:c=

support

con-ditions at the column base. Story shear was distributed

to each column in accordance with its lateral stiffness.The moment distribution of the column was determined by the column shear and the height of inflection point"which was evaluated taking into account :a= the relativelocation of story" :b= the stiffness of ad0acent girdersimmediately above and below the column" :c= changesin the stiffness of the ad0acent girders" and :d= the dif-ference in inter-story height immediately above and below the column. The sum of column end moments ata 0oint was distributed to girder ends in proportion to thegirder stiffness. 6arious factors were prepared in tableformat

for

practical

use.The use of digital computers for the analysis of stati-

cally indeterminate structures began in the mid-19&!s.The enhanced memory" the increased speed of computa-tions and input-output processes" and the efficient use of graphics made it possible to use digital computers inroutine structural design practices. The finite elementmethod for the analysis of continuum structures wasmade possible in the early 19&!s.

3." %eis ic design in 'rban Building (a$ of )apanThe first 8apanese building code" the 7rban *uilding?aw" was promulgated in 1919 to regulate buildings andcity planning in si3 ma0or cities. Structural design wasspecified in *uilding ?aw /nforcement 5egulationsD i.e."quality of materials" allowable stresses of materials"connections" reinforcement detailing" dead and liveloads" and method of calculating stresses were specified" but earthquake and wind forces were not. llowable:working= stress design" whereby the safety factor for uncertainties was considered in the ratio of the strengthto the allowable stress of the material" was in commonuse at this time in the world.

The 19< )anto :Tokyo= earthquake :M (.9= causedsignificant damage in the Tokyo and Cokohama areas"killing more than 1#!"!!!" damaging more than


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vised in 19

Technology suggested in 19 that earthquake responseamplitude of simple systems to transient impulsesshould vary with their natural periods" and introducedthe concept of a response spectrum. @e suggested theuse of an electric analy,er. *iot :19#1=" who later wentto 4olombia 7niversity" developed a mechanical ana-ly,er :torsional pendulum= to calculate the response of linearly elastic systems to an arbitrary e3citing functionDthe 19 % @elena" Montana" earthquake and the 19 ;2erndale" 4alifornia earthquake records were used todevelop the first earthquake response spectra. 'odamping was used in the calculation. @e proposed thatthe undamped response spectrum peaked at !.< s with a

ma3imum

amplitude

of

1.!

"

and

decayed

inversely

i

i


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earthquake resistant design of reinforced concrete buildings by otani (1)

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