base isolation libre

i

2012

Mahmoud S. Ahmed

M.A.Sc., B.Sc.

BUILDINGS WITH BASE ISOLATION TECHNIQUES

ii


By

Mahmoud SAYED AHMED

Ph.D. Candidate, Civil Engineering Department, Ryerson University,

Toronto, ON, Canada, [email protected]

[email protected]

Project Report

Presented to Ryerson University

In partial fulfillment of the

Requirement for the Tall Building course

In the program of

Civil (Structural) Engineering

Toronto, Ontario, Canada, 2012

© Mahmoud SAYED AHMED, 2012

mailto:[email protected]

iii


Mahmoud SAYED AHMED

C.Eng.(Egypt), M.A.Sc., B.Sc.

Abstract

Base isolation (BI) system for buildings is introduced to decouple the building structure

from potentially damaging induced by earthquake motion, preventing the building

superstructures from absorbing the earthquake energy. The mechanism of the base isolator

increases the natural period of the overall structure, and decreases its acceleration response to

earthquake / seismic motion. A steel building with structural rubber bearing is introduced

throughout this study. The study analysis performed to check for the adequacy of the base

isolation against building lateral drift and inter-story drift as per allowance in National Building

Code of Canada 2010. Two buildings were analyzed using the nonlinear time history response

analysis using the dynamic MODAL analysis for fixed base (FB) building, and Isolated base (IB)

building with rubber bearing. The analysis represents a case study for symmetric steel building

to show the ultimate capacity of the selected structural bearing, and to make a comparison for

the difference between the isolated base and the fixed base buildings. Initial results show that

the presence of the structural rubber bearing reduces significantly the vertical displacement,

moment and shear generated for the same mode.

Keywords: building, base isolation, rubber bearing, earthquake, dynamics, time history response

Citation:

Sayed-ahmed, Mahmoud. Building with Base Isolation Techniques. Journal of Al-Azhar University

Engineering Sector (JAUES), Vol. 7, No. 1, Dec. 2012, pp. 147-159.

iv

Acknowledgments

The author would like to thank Prof. Dr. K.M. Anwar Hossain, P.Eng. for his helpful

directions during the course of this research. The author also appreciate the support from

Ryerson University, ON, Canada; library for support and making the available database for

literature review and civil engineering department for offering the SAP2000 to run the modal

analysis.

Disclaimer

The proposed information is for research purpose only, in which its presented data may

provide guidance for a future detailed design procedure. Furthermore any design or analysis

needs a registered professional engineer to design, revise, and stamp for approval. Author claim

no liability to anyone.

v

Contents Abstract ........................................................................................................................................... iii

Acknowledgments ........................................................................................................................... iv

Disclaimer ........................................................................................................................................ iv

List of tables.................................................................................................................................... vii

List of figures .................................................................................................................................. vii

List of Abbreviations ........................................................................................................................ ix

List of Symbols ................................................................................................................................. ix

Chapter I: Introduction .................................................................................................................... 1

1.1 General .................................................................................................................................. 1

1.2 The problem .......................................................................................................................... 1

1.3 The objectives ........................................................................................................................ 3

1.4 The scope ............................................................................................................................... 3

1.5 The contents and the arrangement of the report ................................................................. 3

Chapter II: Literature review ........................................................................................................... 4

2.1 General .................................................................................................................................. 4

2.2 History of base isolation ........................................................................................................ 5

2.2.1 Base-isolation review ..................................................................................................... 6

2.3 Common types of structural bearing .................................................................................... 9

2.3.1 General ........................................................................................................................... 9

2.3.2 Types of structural bearings ......................................................................................... 10

2.3.3 Design of elastomeric structural bearing ..................................................................... 13

2.3.4 Bearing Motion ............................................................................................................. 17

2.4 Earthquake load .................................................................................................................. 18

2.4.1 General ......................................................................................................................... 18

2.4.2 OBC code requirements for earthquake load .............................................................. 20

2.5 Vibration and basic concept ................................................................................................ 25

2.5.1 General ......................................................................................................................... 25

2.5.2 Vibration ....................................................................................................................... 25

2.5.3 Time-History analysis: basic concept ............................................................................ 27

2.5.4 Analysis of dynamics response by mode superposition ............................................... 31

2.6 Base isolation ....................................................................................................................... 34

vi

Chapter III: Parametric Study ........................................................................................................ 44

3.1 General ................................................................................................................................ 44

3.2 Reinforced concrete structure case study ........................................................................... 44

3.2.1 Project description ....................................................................................................... 44

3.2.2 Base-Isolated building .................................................................................................. 48

3.2.3 Fixed base building ....................................................................................................... 55

3.2.4 SAP2000 Model Analysis .............................................................................................. 62

Chapter IV: Conclusions ................................................................................................................. 67

4.1 General ................................................................................................................................ 67

4.2 Conclusions .......................................................................................................................... 67

4.3 Recommendations ............................................................................................................... 68

References ..................................................................................................................................... 69

Bibliography ................................................................................................................................... 70

Appendix ........................................................................................................................................ 71

A: Earthquake ............................................................................................................................ 71

B: Structural bearing .................................................................................................................. 75

C: Earthquake time history ........................................................................................................ 77

vii

List of tables

Chapter II

Table 2. 1 Influential loads on buildings ........................................................................................ 18

Table 2. 2 Importance factor for earthquake load ........................................................................ 22

Chapter III

Table 3. 1 High damping bearing Properties ................................................................................. 45

Table 3. 2 Modal participating mass ratio (MPMR) for fixed and isolated base building ............. 62

Table 3. 3 Modal moment and shear values for edge column B.1 ................................................ 63

Table 3. 4 Joint displacement in column B.1 ................................................................................. 64

Table 3. 5 Joint reactions for column B.1 at the base (Joint 13) ................................................... 65

List of figures

Chapter I

Figure 1. 1 Design procedure for Base Isolation buildings according to NBCC 2005 ...................... 2

Chapter II

Figure 2. 1 Three functions of a bearing [cedengineering.com] ..................................................... 4

Figure 2. 2 Building structure with hybrid control system [Pozo et al 2005] ................................. 7

Figure 2. 3 Base-isolated structure founded on shallow soil layer ................................................. 8

Figure 2. 4 Analytical model for base-isolated structure including soil impedances ...................... 8

Figure 2. 5 External forces of isolated system [Li, H.-N & Wu X.-X 2006] ....................................... 9

Figure 2. 6 Elastomeric bearing [pretread.com] ........................................................................... 11

Figure 2. 7 Roller Bearing [rwsh.de] .............................................................................................. 11

Figure 2. 8 Bolt Rocker bearing [bt-bautechnik-gmbh.de] ............................................................ 12

Figure 2. 9 Pot bearing [agom.it] ................................................................................................... 12

Figure 2. 10 Spherical bearing [Dongil Rubber Belt] ..................................................................... 12

Figure 2. 11 Internal forces which act to displace the rubber from the vertical height lost in

deflection to the unloaded sides [Farat] ....................................................................................... 15

Figure 2. 12 Load-deflection for one and three layer units reinforced with steel plate [Farat] ... 15

Figure 2. 13 The shape factor [Farat] ............................................................................................ 15

Figure 2. 14 Lift-off: Heaヴiﾐg Heha┗ioヴ assuﾏed iﾐ : さseisﾏiI liﾐeaヴﾏodelざ [NCHRP ヵΓヶ]........... 15

Figure 2. 15 Maximum average pressure on a layer of elastomeric bearing at SLS without

rotation [CHBDC] ........................................................................................................................... 16

Figure 2. 16 Building movement ................................................................................................... 17

Figuヴe ヲ. ヱΑ PヴiﾐIipal plates iﾐ eaヴth’s Iヴust ................................................................................. 19

viii

Figure 2. 18 Tectonic plate movement .......................................................................................... 19

Figure 2. 19 Seismic design data for selected locations in Ontario, Canada ................................. 21

Figure 2. 20 Rigid base SDOF system subject to translational component of earthquake ground

motion ........................................................................................................................................... 30

Figure 2. 21 Effective load due to horizontal earthquake ground acceleration ........................... 30

Figure 2. 22 Earthquake base shear [Tedesco, J.W.] ..................................................................... 30

Figure 2. 23 Mechanical model representing MDOF building structure subject to ground

acceleration ................................................................................................................................... 33

Figure 2. 24 Response spectrum for ground motion recorded on Sep 19, 1985 at SCT site in

Mexico City and spectral ordinates for fixed-base and isolated building [] .................................. 36

Figure 2. 25 Natural vibration modes for two buildings [] ............................................................ 37

Figure 2. 26 Friction pendulum sliding (FPS) isolator .................................................................... 39

Figure 2. 27 Relative displacement during chi-chi earthquake [Tsai et al 2003] .......................... 39

Figure 2. 28 Typical Friction Pendulum System ............................................................................. 40

Figure 2. 29 Pasadena City Hall ..................................................................................................... 41

Figure 2. 30 Plan view & cross-section [Forell/Eleseer Engineering, Inc.] .................................... 42

Chapter III

Figure 3. 1 3D Finite element model ............................................................................................. 45

Figure 3. 2 Plan and elevation view ............................................................................................... 46

Figure 3. 3 Combo (Dead plus live) effect on the N-S for Grid A.1 or A.4 ..................................... 47

Figure 3. 4 Response histories (a) displacement of column (joint 15, 13), (b) displacement of

column w.r.t. base, (c) displacement of base shear ...................................................................... 49

Figure 3. 5 Isolated-base – Mode 1 – Period 2.81065 ................................................................... 50

Figure 3. 6 Isolated-base – Mode 2 – Period 2.7975 ..................................................................... 51




Figure 3. 10 Methods to transfer force from column to foundation [Honeck, W.C., Westphal, D.]

....................................................................................................................................................... 55


column w.r.t. base, (c) displacement of base shear ...................................................................... 56

Figure 3. 12 Fixed-base – Mode 1 – Period 0.49310 ..................................................................... 57





Figure 3. 17 Base Isolation joint reactions in joint local coordinate system (MODAL) – Mode 1 . 66

ix

List of Abbreviations

BI Base isolation

CHBDC Canadian Highway Bridge Design Code

CSI control-structure interaction

CQC complete quadratic combination

FEM finite element method

FPS friction pendulum system

HDR high damping rubber

IBC International Building Code

in Inch

kip 1000 pounds-force (4.4482216 kN)

LBR lead rubber bearing

MDOF Multi-degree-of-freedom

NBCC National Building Code of Canada

OBC Ontario Building Code

PGA Peak ground acceleration

PTFE polytetrafluoroethylene

SFRS seismic force resisting system

SDOF Single-degree-of-freedom

SRSS square root of sum of squares

List of Symbols

A area

A pseudo-acceleration

Bx Torsional sensitivity

c damping constant

E modulus of elasticity

f cyclic frequency

F force

g acceleration due to gravity

G shear modulus

h height of floor / layer

H total height

I moment of inertia

Ie earthquake importance factor

J base overturning moment reduction factor

k stiffness

L length

m mass

M moment

M total weight

Mv factor for higher mode

Rd ductility-related force modification factor

Ro overstrength-related force modification factor

S shape factor

S(Ta) spectral response acceleration

Ta fundamental lateral period

u displacement

V shear force

W width

W weight

X,Y,Z directions

ω natural circular frequency

Θ rotation

ζ damping

Δ deflection

σ stress

1

Chapter I: Introduction

1.1 General

Base isolation (BI) is a mechanism that provides earthquake resistance to the new

structure. The BI system decouple the building from the horizontal ground motion induced by

earthquake, and offer a very stiff vertical components to the base level of the superstructure in

connection to substructure (foundation). It shifts the fundamental lateral period, Ta, dissipates

the energy in damping, and reduces the amount of the lateral forces that transferred to the

inter-story drift, and the floor acceleration. The Structural Engineers Association of Northern

Califoヴﾐia ふ“EONCぶ puHlished a siﾏple ヴegulatioﾐ titled さTeﾐtative Isolation Design

Reケuiヴeﾏeﾐtsざ iﾐヱΓΒヶ, ┘hiIh lateヴ ┘as added as provisions in the Uniform Building Code 1997,

FEMA 273 with exception of permit to pushover, and IBC2000.

The structural bearing criteria include vertical and horizontal loads, lateral motion, and lateral

rotation that transferred from the superstructure into the bearing and from the bearing to the

substructure. Bearing allows for stress-free support of the structure in terms of (1) they can

rotate in all directions, (2) they deform in all directions, (3) they take horizontal forces (wind,

earthquake).

1.2 The problem

Reducing the effect of the horizontal forces generated from wind pressure or

earthquake load is of great concern to designers. The structural bearing technique is one of

those tools to reduce the lateral displacement of the building, to increase the structural safety,

and to increase the human comfort during the occurrence of such event. This study tries of

2

clarify the advantage of the base isolation technique with respect to buildings since only few

researches were done into this area. Figure 1 shows the schematic diagram for the design

process for building against earthquake loading as governed by the National Building Code of

Canada 2010 part 4. Clause 4.1.1.4 in NBCC 2010 specifies that buildings and their structural

members shall be designed by one of the following methods (i) analysis based on generally

established theory, (ii) evaluation of a given full-scale structure or a prototype by loading tester

or (iii) studies of model analogues. Throughout this model analogue study the selected building

height will be less than 60 m for regular shape building.

Figure 1. 1 Design procedure for Base Isolation buildings according to NBCC 2005

3

1.3 The objectives

The main objectives of this study work can be stated as follow:

1- To contribute to the efficient design of structural base isolated techniques for buildings

2- To model and investigate a behavior of building with base isolation.

1.4 The scope

The scope of this study includes:

1- Conducting literature review on previous work, and codes of practice to structural

behavior of Base Isolated Buildings

2- Carrying out finite element modeling (FEM) study on two identical building with

different base conditions

1.5 The contents and the arrangement of the report

Chapter II of this report summarizes the literature review on the structural bearing, and

application for buildings with related codes and standards. Chapter III present a case study

conducted on two identical steel buildings, one with base isolation, and other was fixed base for

comparison of the results. Chapter V presents the conclusions of this research, and the

recommendation for future study.

4

Chapter II: Literature review

2.1 General

Base isolation (BI) system for buildings is introduced to decouple the building structure

from potentially damaging induced by earthquake motion, preventing the building

superstructures from absorbing the earthquake energy. The mechanism of the base isolator

increases the natural period of the overall structure, and decreases its acceleration response to

earthquake / seismic motion. Base-isolation relies on the structural bearing, which is the

connection element between the superstructure and substructure to dissipate the horizontal

displacement, rotation or translation, as shown in Figure 2.1. The bearing that prevents

translation is called a fixed bearing or fix point bearing if it is fixed in all directions; it is called a

unidirectional movable bearing or a guided bearing. Base shear introduced due to seismic

ground acceleration for fixed base building or base-isolated building is investigated throughout

this chapter.

Figure 2. 1 Three functions of a bearing [cedengineering.com]

5

2.2 History of base isolation

The fiヴst Hase isolatioﾐ ┘as ヴegisteヴed as a pateﾐt iﾐヱΒヰヰ’s, aﾐd the oﾐe of the fiヴst fe┘

Huildiﾐgs that used the Hase isolatioﾐ ┘as iﾐ eaヴl┞ ヱΓヰヰ’s iﾐ Toko┞o Iﾏpeヴial Hotel, in which

after that structural bearing commercially used in bridge construction. The first material used

for BI was made of lead rubber bearing (LBR) providing high flexibility and damping. In early

ヱΓΒヰ’s the high daﾏpiﾐg ヴuHHeヴふHDRぶ ┘as used iﾐ U“, Hut the dヴa┘HaIk ┘as that these

products have no restoring force where they dislocate after the shaking force. The developed

friction pendulum system (FPS) in shape of spherical surface overcomes this demerit of sliding

bearing, and providing a restoring force. “iﾐIe ヱΒヴヰ’s the ﾐatuヴal ヴuHHeヴ has Heeﾐ used foヴ Hase

isolation, through the process of material development synthetic rubber or

polytetrafluoroethylene (PTFE) which is developed by DuPont was used, and designed for 50

years or more. About 40 years ago, the elastomeric (layered rubber and steel) was used in

bridges, providing an increase of 7% in stiffness after 37 years from installation, with oxidation

restriction to 10 mm to 20 mm. Few design equations were developed for base isolation and

bearing by codes committees like UBC, IBC2000, FEMA273, NZS4203, CHBDC S6, AISI and

AASHTO LRFD foヴ Hヴidges. AIIoヴdiﾐg to the CHBDC, Ilause ヱヱ.ヶ.ヱヱ, it states さBeaヴiﾐg shall

suppoヴt aﾐd tヴaﾐsfeヴ all loads ┘hile aIIoﾏﾏodatiﾐg tヴaﾐslatioﾐs aﾐd ヴotatioﾐs iﾐ the stヴuItuヴeざ,

also added iﾐ Ilause ヱ.Β.ン.ン that さBヴidges ┘ith supeヴstヴuItuヴes suppoヴted on bearings shall be

designed to permit the jacking of the superstructure. Jack and shimming locations shall be

shown on the drawings. The design shall allow for movement at the permanent bearing

loIatioﾐs suffiIieﾐt to peヴﾏit Heaヴiﾐg ヴeplaIeﾏeﾐtざ. Buildiﾐg should have the same provisions

for bearing and its replacement as per CHBDC as well. Nevertheless more provision must be

added for building since it is more complex structure than that of bridges. Due to the presence

of the base isolation, the superstructure of the building above ground needs a transfer slab

6

acting as upper part of the foundation slab, to carry loads from column/frame system. A normal

practice is to locate a bearing at the reaction points at the transfer slab, sometimes lateral

movement is restrained at selected bearing. Design procedures of BI building can be listed as:

(1) response spectrum method, (2) time history analysis, (3) ultimate capacity of isolator, where

a study for the restoring system must be considered.

2.2.1 Base-isolation review

For earthquake resistant construction using base isolation [Noel J, R. 1992] it was found

that more attention should be paid to four points: 1. preparation of guidelines for evaluation

and approval of base isolation structures; 2. preparation of guidelines related to the

performance of base isolation devices; 3. facilities to encourage exchange, collection and

dissemination of technical information on the response-control structure; and 4. study of

methods of evaluation of performance of response-control structures. A study run by Murat &

Senol for the active-passive base-isolation systems used for the seismic response control of

structures appears to be effective for small to medium strength earthquakes. Hybrid base

isolation systems, as shown in Figure 2.2, which use an active system together with the passive

base isolation system, may be used to control the response of structures subjected to larger

ground motions created by larger magnitude earthquakes. The hybrid base isolation system

using passive base isolation pads together with hydraulic type actuators is proposed. The

system, placed between the foundation of the building and its superstructure, is used to

minimize the forces imposed on the superstructure by the earthquake induced ground motion

[Murat, S & Senol, U. 1995] [Pozo et al 2005]. In application for the base-isolation system, the

Historical buildings have relatively low height, are usually massive and their natural vibration

period is rather low.

7

Figure 2. 2 Building structure with hybrid control system [Pozo et al 2005]

Hence if such buildings are located in a seismically active region, using base isolation systems

will be a very effective way for improving their dynamic response. In some cases the

displacements at the base isolation level are rather big and exceed the allowed limits. In such

cases it is recommended to add dampers to the base isolation system [Iskhakov, I. & Ribakov, Y.

2007]. Analytical seismic responses of structures retrofitted using base isolation devices are

investigated by Vasant & Jangid and the retrofitting of various important structures as historical

buildings, bridges, and liquid storage tanks are selected to investigate the effectiveness of the

base isolation in seismic retrofitting. It is observed that the seismic response of the retrofitted

structures reduces significantly in comparison with the conventional structures depicting

effectiveness of the retrofitting done through the base isolation technique [Vasant A & Jangid,

R.S. 2008]. Chia-Ming and Billie F. presented development and experimental verification of an

active base isolation system for a seismically excited building and modeling the complex nature

of control-structure interaction (CSI) [Chia-Ming & Billie F. 2010]. Hyung-Jo et al investigated a

smart base-isolation system using magnetorheological (MR) elastomers, which are a new class

of smart materials whose elastic modulus or stiffness can be adjusted depending on the

8

magnitude of the applied magnetic field. The results further suggest that the feasibility of using

MR elastomers as variable stiffness elements for enhancing the performance of conventional

base-isolation systems [Hyung-Jo et al 2011]. Yannian et al studied the influence of the action of

coupling earthquake to sliding base-isolation structure for 6 story building. The results by

exemplification show that the peak values of relative acceleration, relative displacement and

inter-storey shear force of sliding base-isolation structure increase in different degree under the

action of coupling earthquake [Yannian et al 2011]. Regarding the slide-limited friction base

isolation technology, Gui-Feng & Yu-Hong studied the total restoring force model of isolation

device. They analyzed the influential factors such as friction coefficient, elastic stiffness and yield

displacement of displacement-constraint device on base isolation system [Gui-Feng & Yu-Hong

2011]. Spyrakos et al investigated and developed 2-DOF (degree-of-freedom) for the effect of

soil-structure interaction (SSI) on the response of the base isolated multistory building founded

on elastic soil layer overlaying rigid bedrock and subjected to harmonic ground motion

[Spyrakos et al 2009].

Figure 2. 3 Base-isolated structure founded

on shallow soil layer

Figure 2. 4 Analytical model for base-isolated

structure including soil impedances

9

Figure 2. 5 External forces of isolated system [Li, H.-N & Wu X.-X 2006]

Li & Wu investigated the limitation of height-to-width ration (HWR) for base-isolated building

with elastomeric rubber bearing. It was found that the isolated building with longer period may

have a relatively HWR value: and the stiffness of the superstructure affects HWR limit value little

[Li, H.-N & Wu X.-X 2006]. The main two key conditions, which determine the HWR limit for an

isolated structure, are: (1) the outermost rubber pads of the isolated layer cannot bear tensile

force; (2) the compressive force that the outermost rubber pads bear cannot exceed their

ultimate antipressure strength.

2.3 Common types of structural bearing

2.3.1 General

Base-isolation may be referred to its function, main material, or may receive a combined

terms. The main functions maybe listed as: Point rocker bearing, Sliding bearing, Pot bearing,

Spherical bearing, Deformation bearing, Fixed bearing, Movable bearing, Restraints, and Guide

bearing. The Base-Isolation can be referred to the main material: Steel bearing, PTFE bearing

(polytetrafluoroethylene), and Elastomeric bearing (reinforced/not reinforced). The Base

10

Isolation can also be referred as of combined terms: point rocker sliding bearing, pot sliding

bearing, spherical sliding bearing, and deformation sliding bearing.

2.3.2 Types of structural bearings

In revision to the CHBDC clause 11, the code requires that the bearings (1) carry high

permanent compression load with minimum compression deflection; (2) to accommodate

horizontal movement by shear deflection with low shear stiffness to prevent excessive loads on

the buildings footings due to thermal expansion and contraction; (3) to accommodate rotational

deflections due to the transfer slab hogging and sagging; (4) to accommodate live loads with

minimal additional compressive deflection; (5) to have a natural frequency particular to the

application. The standards recognized the bearing as follows:

- Plain elastomeric

o Natural Rubber (polyisoprene)

o Neoprene (polychloroprene)

- Steel reinforced elastomeric

- Roller bearing

- Rocker bearing

- Pot bearing

- Disc bearing

- Spherical and cylindrical bearing

- Other (require approval)

Where factors affecting the selection criterion include: dead load, total load, lateral load, uplift,

rotations, translations, cost and durability.

11

Pot bearings are designed to carry combinations of vertical loads, horizontal loads,

longitudinal and transversal movements, and rotations. This type of bearing can carry very high

loads of over 50,000 kN. A completely encased natural rubber pad is positioned in a steel pot.

Under high pressure the pad behaves like a liquid. The elasticity of the rubber allows tilting

movement (rotation) of the piston in the horizontal axis [agom.it]. Rolling bearing is a bearing

which carries a load by placing round elements between the two pieces. The relative motion of

the pieces causes the round elements to roll with very little rolling resistance and with little

sliding [wikipedia.org]. Elastomeric bearing developed in 1936 and consists from circular or

rectangular laminated pads, layers made of reinforced rubber, and layers made of steel plates,

the horizontal displacement is resisted by the friction forces F which depends on the

compressive force C of these bearing, and its coefficient of friction p, with F = Cp. Spherical

bearing consists from three main parts; the pan, the sphere part, and the upper plate made of

constructional steel. The horizontal displacement causes friction resistance, and moment due to

rotation.

Figure 2. 6 Elastomeric bearing

[pretread.com]

Figure 2. 7 Roller Bearing [rwsh.de]

http://en.wikipedia.org/wiki/Bearing_(mechanical)

http://en.wikipedia.org/wiki/Rolling

http://en.wikipedia.org/wiki/Rolling_resistance

http://en.wikipedia.org/wiki/Sliding_(motion)

12

Figure 2. 8 Bolt Rocker bearing [bt-bautechnik-

gmbh.de]

Figure 2. 9 Pot bearing [agom.it]

Figure 2. 10 Spherical bearing [Dongil Rubber Belt]

Rocker bearing consist of one or more rollers of steel along with a rocker arrangement which

permits a longitudinal and rotational movement. There are three types of Linear Rocker

Bearings: fixed, guided-sliding and free-sliding Linear Rocker Bearings. Disc Bearing

accommodates rotation by deformation of a single elastomeric disc, molded from a urethane

compound. It may contain a device for partially confining the disc against lateral expansion.

13

2.3.3 Design of elastomeric structural bearing

Rubber bearings is displaced around the edge of the bearing resulting in a bulging when

it is subjected to vertical loading, as shown in Figure 2.11, since rubber itself is incompressible.

Figure 2.12 shows the amount of compressive deflection per unit compressive load (kN/mm)

depends on the bulge of the rubber i.e. shape factor and the shear modulus of the rubber

compound. To achieve an appropriate natural frequency to achieve the required deflection,

elastomeric layer should not be more than 25 mm, in which after that a need to add horizontal

reinforcing plates are moulded into the rubber bearing to reduce the shape factor relative to the

overall height of the bearing and to increase the compressive stiffness of such bearing.

The elastomeric bearing design procedures was adopted for AASHTO LRFD bridge

desigﾐ speIifiIatioﾐ H┞ the NCHRP Repoヴt ヵΓヶさRotatioﾐ liﾏits foヴ elastoﾏeヴiI Heaヴiﾐgざ, aﾐd H┞

the AmeriIaﾐ Iヴoﾐ aﾐd “teel Iﾐstitute ふAI“Iぶ, さ“teel Hヴidge Heaヴiﾐg seleItioﾐ aﾐd desigﾐ guideざ.

[1] Where S is the shape factor, L is the length of the bearing parallel to the span of the bay, W is

width of the bearing, measured perpendicular to the length, as per Figure 2.13. Rubber is not

Ioﾏplete iﾐIoﾏpヴessiHle, aﾐd the effeIt of IoﾏpヴessiHilit┞ iﾐde┝, ゜, de┗eloped iﾐ “taﾐtoﾐ aﾐd

Lund [2006]

[2] √

Where K is the bulk modulus of the rubber, and G is the shear modulus of the rubber. In

designing for rubber bearing the AASHTO LRFD Bridge Design Specification introduced two

methods; Method A that specifies that shear modulus of the elastomer should be between

0.080 ksi and 0.250 ksi, and nominal hardness should be between 50 and 70 on the Shore A

14

scale, and all other physical properties should conform to ASTM D 4014. The service level axial

stress is limited by

[3] ksi

Where σa = the average axial stress, and G = the shear modulus of the elastomer. This stress can

be increased by 10% if the bearing is fixed against shear displacement. The shear deflection is

governed by

[4]

Where hrt is the total thickness of the elastomer. To ensure the lift-off as shown in Figure 2.14

is prevented, the rotation and axial stress must satisfy

[5] 岾峇

Wheヴe θx is the rotation applied to the bearing about x-axis, hrt is the thickness of one rubber

layer, and n is the number of internal rubber layers. Finally the length and the width of the

bearing must be greater than three times the total thickness to prevent instability.

Method B specifies that the shear modulus of the elastomer should be between 0.080 – 0.175

ksi, and the nominal hardness should be between 50 – 60 on Shore A scale, and all other

properties to conform ASTM D 4014. The bearing that is subjected to shear deformation, total

axial stress is governed by:

[6] ksi

Live load stress is required to less than 0.66 GS, and the total stress can be increased to 2.0 GS

and 1.75 ksi if the shear displacement is prevented. The combination of the axial load and

rotation are governed by the need to prevent the lift-off and to avoid excessive shear strain in

the compressive side of the bearing. The governing equation to prevent lift-off

[7] 岾峇

15

Figure 2. 11 Internal forces which act to displace the rubber from the vertical height lost in

deflection to the unloaded sides [Farat]

Figure 2. 12 Load-deflection for one and three layer units reinforced with steel plate [Farat]

Figure 2. 13 The shape factor [Farat] Figure 2. 14 Lift-off: bearing behavior

assuﾏed iﾐ : さseisﾏiI liﾐeaヴﾏodelざ

[NCHRP 596]

16

Figure 2. 15 Maximum average pressure on a layer of elastomeric bearing at SLS without

rotation [CHBDC]

And for preventing excessive shear strain on the compressive side

[8] [ 岾峇 ] These two equations bound the axial stress, rotation pair lying between them will neither lift off

nor cause excessive local compression. In the Canadian Standards CHBDC a set of limitation for

bearing stresses are plotted in Figure 2.15.

17

2.3.4 Bearing Motion

Bearings are allowed to move and rotate with respect to the support plane, rotation and

displacement should be considered in three directions at a right angle to each other. Type of

bearing must be selected prior to the calculation of the bearing movement. The selection

criterion of the bearing depends on a preliminary estimation for the displacement as listed in

below table, and based on the next fix-point: (1) Steel structure: ±0.50 mm/m, (2) Concrete

structures: +0.30 mm/m, -0.60 mm/m, (3) Prestressed concrete structures: +0.30 mm/m, -1.20

mm/m [Eggert, H & Kauschke, W. 2002].

Figure 2. 16 Building movement

Since by code provisions, it is required to make an access to the bearing elements underneath

the superstructure for replacement after their service life. Small columns are likely to be

constructed above the foundation slab to carry the load bearing. Above the bearing, there is a

transfer slab that carries all gravity loads. The bearing deformation at the top of the carrying

base or columns can be expressed as follow:

[9] Where T is the bearing net thickness, A is the bearing area, G is the shear modulus, L,E,I are the

carrying structural element data, FH is the horizontal force, and f is the displacement between

substructure and superstructure.

18

Table 2. 1 Influential loads on buildings

Su

pe

rstr

uct

ure

Outer loads Dead loads

Wind & Earthquake

In Z direction

Horizontal

Restraints Temperature

Shrinkage

Prestressing

Creep

Support settlement

In all directions

In all directions

In prestressing direction

In prestressing direction

In Z direction

Su

bst

ruct

ure

Outer loads Dead loads

Wind & Earthquake

Shock

In Z direction

Horizontal

Horizontal

restraints Temperature

Subsoil motion

In all directions

Z (settlement) direction and rotation about

horizontal axis (rotation of the foundation)

2.4 Earthquake load

2.4.1 General

Earthquake is the sudden release of accumulated energy in the tectonic plates of the

earth crust and resulting in propagation of seismic waves; P waves, S waves and surface waves.

Earthquake occurs at the faults at boundaries the tectonic plates, causing colliding, separation,

sliding, or subducting between the adjacent plates. Epicenter is the ground surface point that

intersects vertically in a line to the depth of the hypocenter, which considered being a significant

factor of seismic hazard. Earthquake magnitude was first introduced with Richter [Richter 1935]

for local magnitude (ML). Richter magnitude can measure the amount of seismic released energy

up to ML 6.5. The surface-wave magnitude (Ms) was developed to solve the saturation problem

of Richter magnitude above ML of 6.5 [Gutenberg 1945]. However this scale was also saturated

at Ms > 8. The short-period body-wave magnitude (Mblg) developed by [Kanamori 1983] for

19

Figure 2. 17 PヴiﾐIipal plates iﾐ eaヴth’s Iヴust

(a) Plate collide (b) Plate separate

(c) Plate slide (d) Plate subduct

Figure 2. 18 Tectonic plate movement

20

North America and Canada tectonic plate, however this scale also get saturated at magnitude

levels less than that of Ms. The moment magnitude (Mw or M) was developed by [Kanamori

1977; Hanks and Kanamori 1979] where it relies on the seismic moment with the following

equation

[10]

Where D is the average displacement over the entire fault surface, A is the area of the fault

suヴfaIe, aﾐd ´ is the a┗eヴage sheaヴヴigidit┞ of the faulted ヴoIk. The seisﾏiI ﾏoﾏeﾐt ヴepヴeseﾐts

the amount of energy released at the source.

[11]

Where Mw is the moment magnitude and Mo is the seismic moment.

Duration (Ta) of the ground motion, the peak ground acceleration (PGA), and the seismic

maps are parameters of great interest to assess the seismic hazardous for the given location.

Based on past seismic events, the Annual Maxima Series (AMS) and the annual probability of

occurrence of earthquakes data for their magnitude, period and location would assess the

acceptable risk for design loads. Codes allow using the static push-off analysis for regular

building less than 60 m of height as in NBCC 2005, and to use the response spectrum method for

other types of buildings.

2.4.2 NBCC code requirements for earthquake load

The static base shear load for structural elements due to earthquake motion shall be

determined according to the procedure given in the following equations [NBCC 2010]

[12]

21

[13]

And for and the seismic force resisting system (SFRS) with an Rd equal to or greater than 1.5, V

need not to be greater than

[14]

Where S(Ta) is the 5% damped spectral response acceleration, expressed as a ratio to

gravitational acceleration, for a period of T; Mv is the factor for higher mode effect on base

shear [Humar & Mahgoub 2003]; IE is the earthquake importance factor; W is the dead load plus

25% of the design snow load plus 60% of the storage load for area used for storage; Rd is the

ductility-related force modification factor; Ro is the overstrength-related force modification

factor [Mitchell et al 2003]; and V is the lateral earthquake design force at the base of the

structure.

Figure 2. 19 Seismic design data without PGA for selected locations in Ontario, Canada

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.5 1 1.5 2 2.5

Sp

ect

ral

Re

spo

nse

Acc

ele

rati

on

,S

Period, T

Toronto

Alexandria

White River

22

Figure 2.15 shows the parameters used to represent seismic hazard for specific geographical

locations are the 5%-damped horizontal spectral acceleration values for 0.2, 0.5, 1.0 and 2.0

seconds periods that have the 2% probability of being exceeded in 50 years. The four spectral

parameters are deemed sufficient to define spectra closely matching the shape of the Uniform

Hazardous Spectra (UHS). Hazardous values are the 50th

percentile (median) value based on

statistical analysis of the earthquake that have been experienced in Canada. The median was

chosen over the mean because the mean is affected by the amount of epistemic uncertainty

incorporated into the analysis. It is the view of the Geological Survey of Canada and the

members of the Canadian National Committee on Earthquake Engineering that the estimation of

the epistemic uncertainty is still too incomplete to adopt into the Code [NBCC 2010].

Buildings are classified by one of the major occupancy and classified in more than one

Importance Category. Table 2.2 shows the importance factor for earthquake loads and effects,

IE, forming part of sentence 4.1.8.5(1) in NBCC 2010. Low Importance Category buildings are

defined as building with low human-occupancy farm buildings as having an occupant load of 1

person or less per 40 m2 of floor area. Normal Importance Category building is used for

residential buildings, High Importance Category building is used for petrochemical facilities, and

Post-disaster Importance Category building is used for hospitals and special buildings.

Table 2. 2 Importance factor for earthquake load

Importance category Ultimate limit state

Low 0.8

Normal 1.0

High 1.3

Post-disaster 1.5

23

The fundamental lateral period, Ta, in the direction under consideration for steel moment frame

[15]

The weight, W, of the building shall be calculated using the formula

[16] ∑

The total lateral seismic force, V, shall be distributed such that a portion, Ft, shall be assumed to

be concentrated ath the top of the building, where Ft, is equal to 0.07 Ta V but need not exceed

0.25V and may be considered as Zero, where the fundamental lateral period, Ta, doesﾐ’t e┝Ieed

0.7 s; the reminder V-Ft, shall be distributed along the height of the building, including the top

level, in accordance with the formula

[17] ∑

The structure shall be designed to resist overturning effects caused by the earthquake forces

determined in the below formula, and the overturning moment at level x, Mx, shall be

determined using the below equation

[18] ∑

Where for hx ≥ ヰ.ヶhn, and for hx < 0.6hn

Where J is the base overturning moment reduction factor

Torsional effect are considered by applying torsional moments about a vertical axis at distance

±0.10Dnx from the centers of mass at each floor derived for each of the following load cases

considered separately [Humar et al 2003] to avoid torsional moment due to accidental

eccentricities:

[19]

24

Where Fx is the lateral force at each level and Dnx is the plan dimension of the building at level x

perpendicular to the direction of seismic loading being considered. Torsional sensitivity will be

considered then by calculating the ration Bx for each level x for each orthogonal direction

[20] ⁄

Wheヴe B is the ﾏa┝iﾏuﾏ of all ┗alues of B┝ iﾐ Hoth oヴthogoﾐal diヴeItioﾐs, δﾏa┝ is the ﾏa┝iﾏuﾏ

story displacement at the extreme points of the structure, at level x in the direction of the

earthquake induced by equivalent static force at distance ±0.10Dnx from the center of mass at

eaIh flooヴ, aﾐd δa┗e is the a┗eヴage displaIeﾏeﾐt at the e┝tヴeﾏe poiﾐt of the stヴucture at level x

by the above mentioned forces.

Based on the lateral deflection calculated for base shear, the largest interstory deflection at any

level shall be limited to 0.01hx for post-disaster buildings, 0.02 hx for schools, and 0.025 hx for all

other buildings.

2.4.2.1. Method of analysis

The Equivalent static force per NBCC 2010, article 4.1.8.7 for the superstructure conditioned to

(a)

(b) Regular structure where h < 60m, and Ta < 2 sec in each of its two orthogonal

directions.

In NBCC 2010, article 4.1.8.16 for foundations required that the foundations shall be capable to

transfer earthquake loads and effects between the building and the ground without exceeding

the capacities of the soil. In case at site where , foundations or basement

walls shall be designed to resist earthquake lateral pressure from backfill or natural ground.

25

2.5 Vibration and basic concept

2.5.1 General

The seismic base isolation is limited by uncoupling the structure from the ground

induced motion in the horizontal directions. By arranging the horizontally active elements

(bearings) between the superstructure (the building and the secondary foundation slab) and the

substructure (base foundation), which may reach to ±300 mm, and reduce the dangerous

horizontal acceleration transmitted into the structure to a permissible level and the natural

frequency down to 1.4 Hz.

Ground motion has magnitude, fault mechanism, and fault distance consistent with site

and represented by the maximum considered ground motion, which is known as earthquake-

induced load. Seismic load performs orthogonal horizontal loading on the building, where it uses

the model response history analysis to capture 90% of the mass structural in each of the two

orthogonal directions [ASCE 7-05]. By the presence of the base isolation systems, the structural-

borne noise must be considered, for example the rail traffic generates a soil-bound vibration

signals ranges 10-80 Hz when building is less than 25 m away from the track beds, while the

average range is approximately 60-250 Hz. The necessary spring compression z to provide a

certain vertical natural frequency can be determined by with fz in Hz and z in mm.

2.5.2 Vibration

The structure undergoes vibration when it is disturbed from its static equilibrium

position and to allow it to vibrate. The vibration analysis is resulting in describing the natural

frequency and damping ratio. This motion that vibrates the building could be resulted from the

wind or earthquake-induced force. The time for the undamped system to complete one cycle of

26

vibration is the natural period of vibration donated as Tn, in units of seconds, which is related to

the ﾐatuヴal IiヴIulaヴ fヴeケueﾐI┞ of ┗iHヴatioﾐ, ωn, in radians per seconds.

[21]

The natural cyclic frequency of vibration is donated by fn for a system executes 1/Tn cycles in 1

second. The cyclic frequency fn its units is (Hz) [cycles per seconds (cps)]

[22]

The ﾐatuヴal IiヴIulaヴ fヴeケueﾐI┞ ωn, natural cyclic frequency fn, and natural period Tn can be

expressed differently as follow

[23] √ √ (rad/sec), √ (Hz), √ (sec)

Wheヴe δst = mg/k, δst is the lateral displacement of the mass due to lateral force mg, g is the

acceleration due to gravity, m is the mass, k is the stiffness

[24] and √

Wheヴe ζ is the daﾏpiﾐg ヴatio, I is the daﾏpiﾐg Ioﾐstaﾐt ﾏeasuヴed H┞ the eﾐeヴg┞ dissipated in a

cycle of free vibration or in a cycle of forced harmonic vibration, and ccr is the critical damping

IoeffiIieﾐt. With deIa┞iﾐg of ﾏotioﾐ afteヴ ┗iHヴatioﾐ the ζ HeIoﾏes sﾏall, √ and this

gives an approximate equation of .

27

2.5.3 Time-History analysis: basic concept

The earthquake response is a base excitation, subjected to an arbitrary ground displacement

xgふtぶ. Ne┘toﾐ’s seIoﾐd la┘ sets foヴth the eケuiliHヴiuﾏ Ioﾐditioﾐ [Tedesco, J.W. 1998].

[25]

Where F1 = inertia force = 岑 ,

FD = damping force = 岌 , Fs = elastic restoring force = ks,

F(t) = externally applied force = 0.

And x(t) is the relative displacement of the mass and xt(t) is the total (absolute) displacement of

the mass. Thus, the equilibrium condition may be expressed

[26] 岑岌

The effective load that induces the dynamic response of this system is defined in recognition of

the fact that the inertia form term (Ft) is proportional to the total motion of the system, while

the damping force (FD) and elastic restoring force (Fs) are proportional to the relative motion of

the system. Therefore,

[27]

It follows that

[28] 岑岑岑 Hence it may be written as

28

[29] 岑岑岌

Or

[30] 岑岌

Where Feff(t) is the effective load, attributed to the horizontal ground acceleration, applied to

the mass m and is given by

[31] 岑

“iﾐIe ω2 = k/m and √

[32] 岑岌岑

Thus, for any arbitrary acceleration of the support 岑 , the relative displacement of the mass

x(t) can be computed from the Duhamel integral expression, for zero initial conditions, as

[33] √ ∫ 岑 √

It is noted that the relati┗e ヴespoﾐse of the stヴuItuヴe is IhaヴaIteヴized H┞ its ﾐatuヴal fヴeケueﾐI┞ ω,

the daﾏpiﾐg faItoヴ ζ, aﾐd the ﾐatuヴe of the Hase e┝Iitatioﾐ岑 . Generally, the undamped

natural frequency is used in place of the damped frequency, and the negative sign is ignored.

[34]

Where

[35] ∫ 岑

29

And R(t) is called the earthquake response integral. The relative displacement x(t) is important in

the earthquake analysis of structures because of strains (and stresses) in the structural

members are directly proportional to the relative displacement. For example, the total shear

force, or base shear, V transferred to the foundation by elastic constraints

[36]

Notice that the base shear is equivalent to the elastic restoring force in the system, Fs(t). The

exact relative velocity 岌 of the mass is obtained by differentiating the relative displacement

x(t), with respect to time, resulting in

[37] 岌 ∫ 岑 √

√ ∫ 岑 √

The absolute acceleration of the mass, 岑 , is obtained by differentiation of 岌 , with respect

to time and noting that 岑岑岑 this yields

[38] 岑 ( )√ ∫ 岑 √

∫ 岑 √

These equations represent the earthquake time-history response for a SDOF structure, where

the effective earthquake force and the elastic restoring force are equivalent at any instant of

time.

[39]

30

Figure 2. 20 Rigid base SDOF system subject to

translational component of earthquake ground

motion

Figure 2. 21 Effective load due to

horizontal earthquake ground acceleration

Figure 2. 22 Earthquake base shear [Tedesco et al 1998]

31

Finally, if the stiffness term k is expressed in terms of the natural circular frequency of the

s┞steﾏ ω, theﾐ the effeIti┗e eaヴthケuake force is equivalent to . Notice here that the

effective earthquake force is expressed as the product of the mass m and the pseudo-

acceleration , but not the absolute acceleration 岑 .

2.5.4 Analysis of dynamics response by mode superposition

In many cases, designers are interest in study the response of the support motions rather than

the applied actions by earthquake. For the base isolation, a typical multi-degree-of-freedom

MDOF system is selected to study the vibration of the tall building. In this mode the mass mi are

lumped (localized) at the floor levels and are interconnected with massless columns that have

the equivalent spring constant Ki. Dashpots represented by the damping constant ci model the

energy dissipation in the system. The shear force at every level is denoted by Vi, and Vn

corresponding to the base shear acting between the structure and the soil, or acting at the base

isolation; 岑 is the ground acceleration, and xi represents the relative displacement of the

building at story level i. The other parameters assess the dynamic response of the structure

subjected to base excitation are the relative velocities 岌 and total acceleration xti at each story.

[40] [ ]{ 岑 } [ ]{ } 岑 [ ]{ 岌 } [ ]{ }

Where 岑 is the ground acceleration and {I} is the unit vector of dimension n. At any floor I

the effective load acting on the mass can be expressed as

[41] 岑

The complete effective load vector is given by the product of the mass matrix and the ground

acceleration 岑 as follow:

[42] { } [ ]{ } 岑

32

Thus the first equation can be written as

[43] [ ]{ 岑 } [ ]{ 岌 } [ ]{ } [ ]{ } 岑 { } The model equations of motion can be expressed as following

[44] [ ]{ 岑 } [ ]{ 岌 } [ ]{ } { } Where [M] and [K] are the model mass and stiffness matrices respectively, [C] is the model

damping matrix, and the effective model force vector { } is given by

[45] { } [ ] [ ]{ } 岑 [ ] { } Wheヴe the teヴﾏ ω is Ialled the ﾐatuヴal IiヴIulaヴ fヴeケueﾐI┞ of the s┞steﾏ, ┘ith uﾐits of ヴadiaﾐs

per second, k is the stiffness and is given by

[46] √ rad/sec

The motion is periodic and repeats itself every T seconds, where

[47]

[48] 岾峇

[49] [ ] [ ] [ ][ ] [ ]

Since the model mass, model stiffness, and modal damping matrices are diagonal, the n

uncoupled equation can be written as follows

[50] 岑岌ヴ = ヱ,ヲ,…..,ﾐ

Where

[51] { } [ ]{ } 岑

The response of the rth mode in normal coordinates at any time t may be obtained by

evaluation of the Duhamel integral expression for the given ground motion

33

[52] 岾峇∫

For undamped system, the above equation can be reduced to

[53] 岾峇∫

The system response in physical coordinate, for relative displacement is then given as

[54] { } ∑ { }

Figure 2. 23 Mechanical model representing MDOF building structure subject to ground

acceleration [Tedesco et al 1998]

34

2.6 Base isolation

The concept of base isolation systems is quite simple by interposing structural elements

with low horizontal stiffness between the structure and the foundation to decouple the

structure from the horizontal components of the ground motion which gives the structure a very

low frequency than both its fixed base and the ground motion [Naeim, F & Kelly, J.M. 1999]. The

deformation of first dynamic mode happens in base isolation while the structure above is rigid;

the deformation of higher modes happens in the structure which is orthogonal to the first mode

and to the ground motion, these higher modes do not participate in the motion; therefore, the

high energy in the ground motion cannot be transmitted to the structure. The base isolation

system does not absorb the energy from the earthquakes but it deflects it through the system

dynamics which is not depending on the damping level, but dampers are important to suppress

resonance at the isolation frequency [Naeim, F & Kelly, J.M. 1999].

For the structural building with fixed base: lumped mass m, lateral stiffness k, and the

lateral damping c, for single-degree-of-fヴeedoﾏ “DF s┞steﾏ ┘ith ﾐatuヴal fヴeケueﾐI┞ ωn, natural

period Tn, aﾐd daﾏpiﾐg ヴatio ζ. The suHsIヴipt f iﾐstead of ﾐ to eﾏphasize foヴ fi┝ed Hase ふ┘ithout

isolation system). The base shear Vb for fixed base building is function of the mass and the

pseudo-acceleration response .

[55] √

[56]

[57]

[58]

35

For the structural building with base isolation; the base slab – transfer slab – has mass

mb with lateral stiffness kb and linear viscous damping cb. Two parameters, Tb the natural

vibration period aﾐd ζb the damping ratio, are introduced to represent the base isolation for one

story building. The base isolation system reduces the base shear because of the natural period

of the first mode, the isolation mode, thus increase in the response period, leading to a smaller

spectral ordinate. The design spectrum gives the pseudo-acceleration and deformation as expressed below

[59]

[60] √

[61]

[62]

[63]

Base-Isolation Building [Lu et al 2012]

36

Effectiveness of base isolation

The main function of the base isolation is to reduce the base shear, for this purpose the

Tb/Tf period ratio should be as large as practical, otherwise it will be harmful. Case study 1; for

example during 1985 in Mexico City and for one-story building the recorded earthquake with

pseudo-acceleration value = 0.25g associated with Tf = 0.ヴ seI aﾐd ζf = 2% for the fixed-

base structure, and = 0.63g associated with Tb = ヲ.ヰ seI aﾐd ζb = 10% for the isolated

structure. The ratio / = 0.63g/0.25g = 2.52. This means that the base shear in

the base-isolated building is 2.52 times the base shear in the fixed-base building as Tb>>Tf,

where it is appropriate to select system with the studied factors [Chopra, A.K. 2001].

Figure 2. 24 Response spectrum for ground motion recorded on Sep 19, 1985 at SCT site in

Mexico City and spectral ordinates for fixed-base and isolated building [Chopra 2001]

37

(a) fixed-base building; (b) isolated building

Figure 2. 25 Natural vibration modes for two buildings [Chopra 2001]

An example for multi-degree-of-freedom (MDOF) system, case study 2; is a five-story shear

frame building with lumped mass m = 100 kips/g at each floor, and stiffness k for each floor, the

fundamental period Tf = 0.4 sec, the classical damping matrix cf = a1kf with 2% of damping a1 for

the fundamental mode. The base slab mb = m. The isolation system has a fundamental period of

Tb = ヲ.ヰ seI aﾐd ζb = 10%. The modal damping ratios for both systems are shown in Figure 2.25.

The fiヴst ﾏode foヴ Hoth s┞steﾏs of daﾏpiﾐg ζb = 10% shows that earthquake-induced force for

the first mode is increasing non-linearly for the fixed-base, and almost increased in constant rate

for the base-isolated structure all-over its height. For the other modes, the base mass is acting

as a fixed base afterward. In calculating of the square root of the sum of the squares (SRSS) base

38

shear Vb with respect to the building weight W for the fixed-based building Vb/W = 1.613, and

the Vb/W = 0.361 for the isolated building. This means that the base shear in the base-isolated

building is 3.49 times less than the base shear for the fixed-base building, where Tf>>Tb.

For moderate-to-high-rise building, the effect of higher modes can be approximately

distributed using the general modal relationship shown in Table 2.3, where the fundamental

period of vibration may be calculated using the code formulas, and the periods for the second

through the fifth modes can be estimated by using tabular values.

Table 2. 3 General modal relationship

Mode 1 2 3 4 5

Ratio of period to 1st

mode period 1.000 0.327 0.186 0.121 0.083

Participation factor at roof 1.31 -0.47 0.24 -0.11 0.05

Base shear participation factor 0.828 0.120 0.038 0.010 0.000

Case study 3: Seismic Rehabilitation of Pasadena City Hall

The friction pendulum sliding FPS isolator, as shown in Figure 2.26 has a great impact in

reducing the base shear effect as shown in Figure 2.27. Figure 2.28 show structural detailing for

the proposed system, which was successfully used in In California, U.S., for the historical

Pasadena City Hall, as shown Figures 2.29 & 2.30. The building was rehabilitated with the

seismic isolation that consists of removal of the original basement floor slab, excavation and

installation of new foundation, placement of a new basement transfer system, and installation

of 240 friction pendulum sliding (FPS) isolators between the foundation and basement level.

39

Figure 2. 26 Friction pendulum sliding (FPS) isolator

Figure 2. 27 Relative displacement during chi-chi earthquake [Tsai et al 2003]

40

Figure 2. 28 Typical Friction Pendulum System

41

(a) Main entrance

(b) Top view

Figure 2. 29 Pasadena City Hall

42

Figure 2. 30 Plan view & cross-section [Forell/Eleseer Engineering, Inc.]

43

Table 2. 4 List of major retrofitting buildings projects completed using base isolations [Matsagar

& Jangid 2008]

44

Chapter III: Parametric Study

3.1 General

This chapter is a study analysis for a steel structure building subjected to earthquake-

induced load, with two scenarios; (a) fixed base building and (b) base-isolated building with

rubber bearing. Both buildings are identical expect in the base fixation, and were modeled by

SAP2000 (ver. V14.1.0 Advanced) for nonlinear time history analysis.

3.2 Reinforced concrete structure case study

3.2.1 Project description

A two story building made of steel structure, Figure 3.1, with 3 bays of 30 feet in each

direction, the story height is 12 feet, as shown in Figure 3.1. The structural steel has the

following spec; the modulus of elasticity E = 29000 ksi (A992Fy50), Poisson ratio equals to 0.3,

the beam section is W24x55, the column section is W14x90. The horizontal slabs are reinforced

concrete of 4000 psi and 6 in, 10 in of thickness for the roof and the floor respectively. The

vertical loads for roof is 75 psf for the dead load (DL) and 20 psf for live load (LL), while for the

floor is 125 psf for DL, and 100 psf for LL. Diaphragm constraints at each level is assigned to

make all diaphragm rigid. This project was subjected to nonlinear time history analysis, where

seismic load is applied by SAP2000 for lacc_nor-1 file data in the X-direction and lacc_nor-2 file

data in the Y-direction simultaneously. Each time history is given in units of cm/sec2, where

there are 3000 time steps, at equal spacing of 0.02 sec, for total of 60 sec. There are 8

acceleration points per line. This building is analyzed under two cases; case 1 with fixed base,

and case 2 with isolated base. The rubber isolator has specification listed in table 3.1.

45

Table 3. 1 High damping bearing Properties

Vertical (axial) stiffness 10,000 k/in (linear)

Initial shear stiffness in each direction 10 K/in

Shear yield force in each direction 5 kips

Ratio of post yield shear stiffness to initial shear stiffness 0.2

Figure 3. 1 3D Finite element model

46

(a) Plan view

(b) Elevation view

Figure 3. 2 Plan and elevation view

47

(a) Moment 3-3 Diagram

(b) Axial Force Diagram

Figure 3. 3 Combo (Dead plus live load) effect on the N-S for Grid A.1 or A.4

Figure 3.2 shows the plan and elevation views for the 2story 3 bays building. Further in this

chapter will focus on column at axis B.1, second column from the left, where the base joint is

called as Joint 13, and the first floor joint is called Joint 14, and the roof joint is called Joint 15.

Figure 3.3.a shows the bending moment for columns and beams for the structural frame for the

gravity load (dead + live load), the bending moment for column B.1 is -52.402, 54.384, -29.742

and 42.203 kip-in at Joints 13, 14, 14, and 15 respectively. Figure 3.3 depict the axial force for

48

columns on axis 1 and 4. It was observed that axial load due gravity load is -76.917 and -220.477

kip for the second and first floor respectively.

3.2.2 Base-Isolated building

The base isolation extends the fundamental lateral period resulting in reducing the base

shear forces, enhancing the total building drift to the total height and the inter-story drift if

compared with the conventional foundations. Figure 3.4.a depicts the time response history for

column B.1 with its three joints; Joint 13-15, the figure shows that the column from the base to

the roof level moves laterally in a same rate, thus no deflection occurs at the joint 14, Figure

3.4.b depicts the B.1 column movement with respect to the base, and shows that to great extent

the column move with base. Figure 3.4.c depicts the displacement of the base shear to the

earthquake with respect to time.

It is worth mention that the change in the fundamental period changes the moment, and

consequently changes the building deformation. Figures 3.5 through 3.9 depict the moment 3-3

diagram and the deformation shape for five different MODAL with different periods -. It was

observed that with the decrease of the period, the structure laterally deforms more. Lateral

deformation for building is usually assessed by the shear rigidity index (SRI), bending rigidity

index (BRI), the drift index (DI) and the inter-story drift (ISD). The last two criterions can be

expressed as following:

[64] ⁄

[65] ⁄

Wheヴe Δi is the deflection at the roof; Hi is the total height of the building, hi is the floor height.

49


column w.r.t. base, (c) displacement of base shear

50

(a) Moment 3-3 Diagram (MODAL) Model 1 – Period 2.81065

(b) Deformation shape (MODAL) – Mode 1 – Period 2.81065

Figure 3. 5 Isolated-base – Mode 1 – Period 2.81065

51




52




53




54




55

3.2.3 Fixed base building

The fixed base for the steel columns, as shown in Figure 3.10 which relies on the steel

plate and anchored bolts, reduce the fundamental lateral period resulting in increasing the base

shear forces, increasing the total building drift to the total height and the inter-story drift if

compared with the base-isolated foundations. Figure 3.11.a depicts the time response history

for column B.1 with its three joints; Joint 13-15, the figure shows that the column from the base

to the roof level moves laterally in an independent rate, thus deflection occurs at the joint 14,

Figure 3.11.b depicts the B.1 column movement with respect to the base, and shows that Joint

13 move the base while joint 14, and 15 move independently. Figure 3.11.c depicts the

condensed wave displacement of the base shear in response to the earthquake-induced load. It

is worth mention that the change in the fundamental period changes the moment, and

consequently changes the building deformation. Figures 3.12 through 3.15 depict the moment

3-3 diagram and the deformation shape for five different MODAL with different periods -. It was

observed that with the decrease of the period, the structure laterally deforms more.

Figure 3. 10 Methods to transfer force from column to foundation [Honeck, W.C., Westphal, D.]

56


column w.r.t. base, (c) displacement of base shear

57



Figure 3. 12 Fixed-base – Mode 1 – Period 0.49310

58




59




60




61




62

3.2.4 SAP2000 Model Analysis

The fundamental lateral period was solved using the finite element analysis (FEA)

software, SAP2000. Table 3.3 shows that the fundamental period (T) and the corresponding

frequency (ƒ=1/T) for the Modal participating mass ratio (MPMR) solved for Ritz Vector Analysis,

for the steel building under investigation in this study which has two scenarios; (a) fixed base,

and (b) the isolated base. It was found that the isolated base is 5.699, 6.337, 6.895, 1.64, 1.766

times for Modal 1 through 5 respectively. The first three modes were significantly higher, where

they absorb more than 95% of the earthquake-induced load.

Table 3. 2 Modal participating mass ratio (MPMR) for fixed and isolated base building

Modal

Mode

Period, T [seconds] Frequency, ƒ [Hz]

Fixed Base Isolated Base Fixed Base Isolated Base

1 0.49310 2.81065 2.0279 0.35578

2 0.35973 2.79750 2.7799 0.35746

3 0.35117 2.42137 2.8476 0.41298

4 0.19916 0.32664 5.0211 3.06147

5 0.14006 0.24728 7.1397 4.04399

Where ƒ ≥ 1 Hz for rigid building, ƒ < 1 Hz for flexible building

Moment and shear forces generated from each mode are of great concern to designers, to

predict the failure modes, progressive collapse of the building, or to add extra bracing to resist

such lateral loading. Table 3.4 analyze the moment and shear values for column B.1 and its 3

joints under five different MODAL periods (modes) for minor (V3, M2) and major (V2, M3).

Selection the moment and shear values for the roof, it was found that the moment for the fixed

base building is higher than that of the isolated base building by 51.38, 20455, 0.31, 2.34 and

2.23 for mode 1 through 5 respectively for the minor (M2), and 70, 106, 66, 13.7, and 2.289 for

mode 1 through 5 respectively for the major (M3). Hence the base isolation enhances the

building capacity to resist the earthquake-induced load, and that reduction in moment could be

used towards reducing the selection members sizes, reducing the total building weight and cost.

63

Table 3. 3 Modal moment and shear values for edge column B.1

H

Modal 1 Modal 2 Modal 3 Modal 4 Modal 5

Moment Shear Moment Shear Moment Shear Moment Shear Moment Shear

Iso

late

d-B

ase

Min

or

(V3

, M

2)

288 10.95 -0.146 -0.012 2.4E-4 -3.452 0.047 1104.155 -15.399 -423.458 5.990

144 -10.06 -0.146 0.022 2.4E-4 3.375 0.047 -1110.116 -15.399 437.875 5.990

144 29.27 -0.411 -0.035 5.2E-4 -8.186 0.115 1431.488 -20.376 -536.685 7.627

0 -29.27 -0.411 0.040 5.2E-4 8.403 0.115 -1502.657 -20.376 561.644 7.627

Ma

jor

(V2

, M

3)

288 4.5E-3 2.3E-4 14.804 -0.19 22.168 -0.28 -0.246 0.022 2765.094 -37.176

144 0.038 2.3E-4 -12.55 -0.19 -18.120 -0.28 2.864 0.022 -2588.261 -37.176

144 -0.086 1.4E-3 32.193 -0.457 49.083 -0.698 -4.993 0.072 3107.763 -45.283

0 0.112 1.4E-3 -33.644 -0.457 -51.388 -0.698 5.389 0.072 -3413.022 -45.283

Fix

ed

-Ba

se

Min

or

(V3

, M

2)

288 562.661 -7.645 245.464 -3.435 1.067 -0.023 -2586.53 38.47 944.549 -13.976

144 -538.23 -7.645 -249.23 -3.435 -2.209 -0.023 2921.005 38.47 -1068.03 -13.976

144 1133.21 -16.52 403.782 -5.849 2.217 -0.023 1862.977 -25.378 -691.367 9.451

0 -1245.9 -16.52 -438.537 -5.849 -1.082 -0.023 -1791.469 -25.378 669.645 9.451

Ma

jor

(V2

, M

3)

288 -0.315 0.021 -1569.76 20.652 -1477.367 19.656 3.372 -0.038 -6329.895 94.133

144 2.776 0.021 1404.129 20.652 1353.073 19.656 -2.092 -0.038 7225.272 94.133

144 -3.192 0.031 -2430.91 37.054 -2251.606 34.076 0.841 -8.2E-3 4966.383 -66.903

0 1.321 0.031 2904.872 37.054 2655.291 34.076 -0.348 -8.2E-3 -4667.693 -66.903

H is the building height in [in], M is the moment in [kip-in], V is the shear force in [kip]

64

Table 3. 4 Joint displacement in column B.1

Modal

Mode

Joint Fixed Base Isolated Base

[Height] U1 U2 U3 U1 U2 U3

15 [288] -9.2E-14 -0.7459 -0.0032 -2.2E-11 -0.4699 -0.0001

1 14 [144] -5.4E-14 -0.4597 -0.0025 -2.2E-11 -0.4642 -0.0001

13 [0.00] 0.00 0.00 0.00 -2.2E-11 -0.4518 -4.8E-5

15 [288] 0.8412 -0.2804 -0.0026 -0.4659 1.9E-11 2.3E-5

2 14 [144] 0.4806 -0.1602 0.0021 -0.4625 1.8E-11 2.1E-5

13 [0.00] 0.00 0.00 0.00 -0.456 1.8E-11 1.1E-5

15 [288] 0.7684 1.6E-13 -0.0013 -0.5141 0.1714 6.7E-5

3 14 [144] 0.4362 9.0E-14 -0.001 -0.5088 0.1696 6.0E-5

13 [0.00] 0.00 0.00 0.00 -0.4987 0.1662 2.9E-5

15 [288] 1.19E-14 0.5858 0.0073 -3.3E-14 -0.6543 -0.0086

4 14 [144] -1.03E-14 0.5853 0.0043 -1.8E-15 -0.1044 -0.0073

13 [0.00] 0.00 0.00 0.00 2.6E-14 0.5306 -0.0031

15 [288] 0.6114 -0.2038 -0.0062 -0.727 0.2423 0.0066

5 14 [144] -0.6612 0.2204 -0.0034 -0.1064 0.0355 0.0056

13 [0.00] 0.00 0.00 0.00 0.0025 -0.1926 0.5778

Where U1, U2, U3 are displacement in x, y, z directions respectively in [in]; Height in [in]

Drift is another point of interest to designers and must conform to code requirements. Table 3.5

shows the deflections in x, y, z directions for the edge column B.1 under the different 5 MODAL

(periods) for the fixed base and the isolated base building. The major observation to this table is

that the defleItioﾐ foヴ the Hase isolated Huildiﾐg doesﾐ’t staヴt fヴoﾏ zeヴo, thus ヴeduIes

significantly the drift index for the building. For example in studying the drift index (DI) for

MODAL mode 1, the drift index for the isolated base = (0.46999 – 0.4518)/288 = 0.063159E-3 in,

while for the fixed base building DI = (0.7459 – 0)/288 = 2.589E-3 mm, which means that the

deflection in base isolated building is less by 40.99 times than that of the conventional fixed

structure. The joint reactions in Table 3.5 are obtained using modal combination applied

65

individually to each joint. The joint reactions are represented as Ri,m where is (i) is for the

direction, and (m) for mode. The total reaction follows this equation

[66] √∑

Table 3. 5 Joint reactions for column B.1 at the base (Joint 13)

Structure Type Type Joint reaction [kip]

1 2 3

Isolated Base

Modal1 0.000 0.678 0.480

Modal 2 0.684 0.000 -0.108

Modal 3 0.748 -0.249 -0.291

Modal 4 0.000 -0.796 31.454

Modal 5 -0.867 0.289 -24.722

Gravity 0.000 0.000 361.487

Fixed Base

Modal 1 -3.134E-2 16.522 13.514

Modal 2 37.054 5.849 10.948

Modal 3 -34.076 2.291E-2 5.603

Modal 4 8.258E-3 25.378 -22.900

Modal 5 66.903 -9.451 18.251

Gravity 0.179 0.404 360.799

Directions 1, 2, 3 represent X, Y, Z axis respectively; Gravity load equals to dead and live load

For example the joint reaction , Figure 3.17, for the isolated base building in X-direction equals

to SQRT (0.6842+0.748

2+0.867

2) = 1.33 kips, while for the fixed base building it is equal to SQRT

(3.134E-22+37.054

2+34.076

2+8.258E-3

2+66.903

2) = 83.727 kips. Apparently, the joint reaction in

fixed base building for column B.1 in X-direction is higher by 62.95 times than that of the base

isolated building. While the base reactions for response spectrum are computed for each mode

and then the modes are combined using CQC or SRSS modal combination rule:

[67] ∑

[68] √∑

Where for the base reaction, all join reactions from all columns must be computed [CSI 2012].

66

Figure 3. 17 Base Isolation joint reactions in joint local coordinate system (MODAL) – Mode 1

67

Chapter IV: Conclusions

4.1 General

This study presents both theoretical investigation and modeling for building subjected

to earthquake-induced load with fixed base and with base-isolated method using rubber

bearing. The objective of this work is to contribute to the efficient design of base-isolated

structure subjected to seismic ground motion. The following sections summarize the conclusions

resulting from this research work as well as recommendations for future research.

4.2 Conclusions

Based on the theoretical and modeling findings, the following conclusions can be drawn:

The main observation from the modeling study on the accuracy of seismic effect and

lateral load patterns utilized in the Multi-Modal Pushover analysis (MPA) in predicting

earthquake effect showed that the accuracy of the pushover results depends strongly

on the load path, properties of the structure and the characteristics of the ground

motion.

The lateral deflection for MDOF for multi-story building can be represented as SDOF

once the equivalent mass and stiffness is obtained.

The plastic hinge location varies by the type of loading, and the change in MODAL

period. It can be located at any point along the span of member as well as the end of the

member.

Drift index and inter-story drift should be predicted using the multi-modal (SRSS) and

the elastic first mode with long period for the lateral load pattern which corresponds to

the average in most cases.

68

Base-isolated structure exhibit less lateral deflection, as the lateral displacement at the

base never equals to zero, and less moment values than the fixed base structure.

The base isolation decouples the building from the earthquake-induced load, and

maintain longer fundamental lateral period than that of the fixed base.

4.3 Recommendations

1. Study the influence of the structural bearing properties and the stresses generated from

tilting of the superstructure due to lateral loading.

2. Study the potential for liquefaction of the soil and its consequences on base-isolated

buildings.

3. Establish design procedures and guidelines for Base-Isolation structure.

69

References

Al-Hussaini, T.M., Zayas, V.A., Constantinou, M.C., "Seismic Upgrade of Multi-Story Buildings

Using the Friction Pendulum Isolation System," Proc., Tall Buildings in Developing

Countries, International Conference on Tall Buildings, Dhaka, Bangladesh, June, 1993.

C. Chia-Ming and B. F. Spencer, Jr., "An Experimental Study of Active Base Isolation Control for

Seismic Protection," in Sensors and Smart Structures Technologies for Civil, Mechanical,

and Aerospace Systems 2010, 8-11 March 2010, USA, 2010, p. 76473V (12 pp.).

Chopヴa, A.R., さD┞ﾐaﾏiIs of stヴuItuヴes,ざ PヴeﾐtiIe-Hall, New Jersy, USA, 2001.

C.-M. Chang and B. F. Spencer, "Active base isolation of buildings subjected to seismic

excitations," Earthquake Engineering and Structural Dynamics, vol. 39, pp. 1493-1512,

2010.

C.-M. Chang and B. F. Spencer Jr, "An experimental study of active base isolation control for

seismic protection," in Sensors and Smart Structures Technologies for Civil, Mechanical,

and Aerospace Systems 2010, March 8, 2010 - March 11, 2010, San Diego, CA, United

states, 2010, pp. The Society of Photo-Optical Instrumentation Engineers (SPIE);

American Society of Mechanical Engineers; KAIST.

C“I, さHase ヴeaItioﾐs foヴヴespoﾐse speItヴuﾏ,ざ ┘eHsite: https://wiki.csiberkeley.com/display/kb/

Base+reactions+for+response+spectrum+analysis, accessed March 2012.

Eggert, H., Kauschke, W., さStructural Bearings,ざ Ernst & Sohn, Germany, 2002.

G.-F. Zhao and Y.-H. Ma, "Parameters study of rural buildings structures supported on slide-

limited friction base isolation system," Zhendong yu Chongji/Journal of Vibration and

Shock, vol. 30, pp. 148-152, 2011.

G. Sun and A. Li, "Dynamic reliability analysis and parameter optimization of base isolation

structure," Journal of Southeast University (Natural Science Edition), vol. 39, pp. 320-7,

2009.

H.-J. Jung, et al., "Seismic performance analysis of a smart base-isolation system considering

dynamics of MR elastomers," 55 City Road, London, EC1Y 1SP, United Kingdom, 2011,

pp. 1439-1450.

HoﾐeIk, W.C. aﾐd Westphal, D., さPヴaItiIal desigﾐ aﾐd detailiﾐg of steel Ioluﾏﾐ Hase plates,ざ Forell Elsesser Engineers, Inc, July 1999.

Huﾏaヴ, J., Ya┗aヴi, “., aﾐd “aatIioglu, M., さDesigﾐ foヴ foヴIes iﾐduIed H┞ seisﾏiI Toヴsioﾐざ. Caﾐ. J.

Civ. Eng., vol. 30, pp. 328-337, 2003.

Huﾏaヴ, J., aﾐd MahgouH, M.A., さDeteヴﾏiﾐatioﾐ of seisﾏiI desigﾐ foヴIes H┞ equivalent static load

ﾏethod,ざ Caﾐ. J. Ci┗. Eﾐg., ┗ol. ンヰ, pp. ヲΒΑ-307, 2003.

I. Iskhakov and Y. Ribakov, "Modern trends in base isolation applications for seismic protection

of historic buildings," in 10th International Conference on Studies, Repairs and

Maintenance of Heritage Architecture, STREMAH 2007, June 4, 2007 - June 6, 2007,

Prague, Czech republic, pp. 623-632, 2007.

J.-g. Sun, et al., "Experimental research on rubber base-isolation tank," Journal of the Harbin

Institute of Technology, vol. 37, pp. 806-9, 2005.

Li, H.-N, Wu, X.-X., さLiﾏitatioﾐ of height-to-width ration for base-isolated buildings under

eaヴthケuakeざ, “tヴuItuヴal Desigﾐ of Tall Special Building, vol. 15, pp. 277-287, 2006.

Lu, L., Chu, “., Yeh, “., Chuﾐg, L, さ“eisﾏiI test of least-input-energy control with ground velocity

feedback for variable-stiffﾐess isolatioﾐ s┞steﾏsざ, Jouヴﾐal of souﾐd aﾐd ┗iHヴatioﾐ, ┗ol. ンンヱ, Oct., pp. 767-784, 2012.

https://wiki.csiberkeley.com/display/kb/%20Base+reactions

https://wiki.csiberkeley.com/display/kb/%20Base+reactions

70

MitIhell, D., TヴeﾏHla┞, R. KaヴaIeHe┞li, E., Paultヴe, P., “aatIioglu, M., aﾐd Aﾐdeヴsoﾐ, D., さ“eisﾏiI force modification factors for the proposed 2005 edition of the National Building Code of

Caﾐada,ざ Caﾐ. J. of Ci┗. Eﾐg., ┗ol. ンヰ, pp. 308-327, 2003.

Matsagaヴ, V.A.,aﾐd Jaﾐgid, R.“. さBase isolatioﾐ foヴ seisﾏiI ヴetヴofittiﾐg of stヴuItuヴes,ざ PヴaItiIe Periodical on Structural Design and Construction, vol. 13, No. 4, pp. 175-185, Nov 1,

2008.

M. Sener and S. Utku, "Active-passive base isolation system for seismic response controlled

structures," in Proceedings of the 36th AIAA/ASME/ASCE/AHS/ASC Structures,

Structural Dynamics, and Materials Conference and AIAA/ASME Adaptive Structures

Forum. Part 1 (of 5), April 10, 1995 - April 13, 1995, New Orleans, LA, USA, 1995, pp.

2350-2359.

M. Sener and S. Utku, "Control of torsional modes in buildings under seismic excitation by

adaptive base isolation," in Smart Structures and Materials 1996: Passive Damping and

Isolation, Febrary 26, 1996 – Feb. 27, 1996, San Diego, CA, USA, 1996, pp. 145-156.

M. Sener and S. Utku, "Adaptive base isolation system for the control of seismic energy flow into

buildings," Journal of Intelligent Material Systems and Structures, vol. 9, pp. 104-15,

1998.

Naeim, F & Kelly, J.M. 1999

N. J. Raufaste, "Earthquake resistant construction using base isolation," Publ by Natl Inst of

Standards & Technology, Gaithersburg, MD, United States, 1992.

NRCC, さNatioﾐal Buildiﾐg Code of Caﾐada,ざ AssoIiate Coﾏﾏittee oﾐ the Natioﾐal Buildiﾐg Code,

National Research Council of Canada, Ottawa, ON, 2005.

Pozo, F., Ikhouaﾐe, F., aﾐd Pujol, G., さAdapti┗e HaIksteppiﾐg Ioﾐtヴol of h┞steヴetiI Hased-isolated

stヴuItuヴes,ざ Jouヴﾐal of ViHヴatioﾐ aﾐd Coﾐtヴol, ┗ol. ヱヲ, issue ヴ, pp. ンΑン-394, 2006.

R. S. Jangid, "Optimum damping in a non-linear base isolation system," Journal of Sound and

Vibration, vol. 189, pp. 477-87, 1996.

TedesIo, J.W., MIDougal, W.G., aﾐd Ross C.A., さ“tヴuItuヴal d┞ﾐaﾏiIs: Theoヴ┞ aﾐd appliIatioﾐs,ざ Prentice Hall, USA, 1998.

Tsai, C.S., Chiang,T.,-C, & Chen, B.-J., さFiﾐite eleﾏeﾐt foヴﾏulatioﾐs aﾐd theoヴetiIal stud┞ foヴ ┗aヴiaHle Iuヴ┗atuヴe fヴiItioﾐ peﾐduluﾏ s┞steﾏざ, Eﾐgiﾐeeヴiﾐg stヴuItuヴes, ┗ol. ヲヵ, pp. ヱΑヱΓ-

1730, 2003.

Y. Zhang, et al., "Parameters optimization of sliding base-isolation structure under the action of

coupling earthquake," in 1st International Conference on Civil Engineering, Architecture

and Building Materials, CEABM 2011, June 18, 2011 - June 20, 2011, Haikou, China,

2011, pp. 4021-4027.

V. A. Matsagar and R. S. Jangid, "Base isolation for seismic retrofitting of structures," Practice

Periodical on Structural Design and Construction, vol. 13, pp. 175-185, 2008.

Bibliography Mahmoud has more than 12 years of experience in the field of civil engineering. He has worked

as civil (structural) engineer for 9 years in The Engineers Brothers Company, Cairo, Egypt. He also

worked as Research & Graduate Assistant in Ryerson University, ON, Canada. He worked in

EPCM (Engineering, Procurement, and Construction Management) industry for ICI (industrial,

commercial & institutional) Buildings. He conducted research in the field of sandwich structure,

glass fibre reinforced polymers (GFRP), post-tensioning, and bridges. Mahmoud has published 3

technical papers.

71

Appendix

A: Earthquake

A.1 Canadian seismic hazard map

72

A.2 Seismic acceleration in Canada

A.3 Spectral response acceleration map Sa(0.2)

73



74


2010 National Building Code of Canada seismic hazard maps

[Source: www.earthquakescanada.nrcan.gc.ca]

The four spectral acceleration seismic hazard maps show levels of ground shaking at periods of

0.2, 0.5, 1.0 and 2.0 seconds (equivalent to frequencies of 5, 2, 1, and 0.5 Hertz). A high-rise of

ten stories or more may sway with a natural period of 1 or 2 seconds, whereas in response to

the same earthquake a brick bungalow across the street may vibrate at nearly 10 Hertz.

75

B: Structural bearing

B.1 Selection guide for small rotation [AISI]

B.2 Selection guide for moderate rotation [AISI]

76

B.3 Selection guide for large rotation [AISI]

77

C: Earthquake time history

C.1 Time history function – LACC0

C.2 Time history function – LACC1

Citation:

Sayed-ahmed, Mahmoud. Building with Base Isolation Techniques. Journal of Al-Azhar University

Engineering Sector (JAUES), Vol. 7, No. 1, Dec. 2012, pp. 147-159.

base isolation libre

Documents

fixed base buildings

base isolator

isolated base ib building

fixed base fb building

building structure

building superstructures

building lateral drift

symmetric steel building