Lect 7 Seismic

7/24/2019 Lect 7 Seismic

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Earthquake Resistant Design ofConcrete Structures

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Contents

Introduction

Behaiour of Structures

Introduction to IS 1!"# Seis$ic Coe%cient &ethod

Res'onse S'ectru$ &ethod

Ductile Detailing as 'er IS 1#"20



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Anal(sis

Basic equation of force &) * c+ * k, - ./,

ur task is to nd out ,34 hence 5aseshear6

Static Anal(sis

D(na$ic Anal(sis

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inear static8on linearstatic

inear d(na$ic8on lineard(na$ic

Eq6 static$ethod9ushoeranal(sisRes'onses'ectru$

:i$e histor(


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IS;1!"#

Code is onl( for ensuring $ini$u$require$ents6 8ot as a BIBE6 Sounderstanding the code is i$'ortant

IS;1!"# rst 'u5lished in 1"4 and no?in 20026

Beginning 20024 this code is 5eing s'lit intoseeral 'arts So that reisions can take 'lace $ore frequentl(@

nl( 9art 14 9art I of the code hae 5een'u5lished6 ther 'arts $a( take a ?hile6

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Dierent 9arts of IS;1!"#

9art 1; eneral 9roisionsand Buildings 9art 2; iquid Retaining :anks Eleated

and round Su''orted

9art #; Bridges and Retaining alls 9art >; Industrial Structures Including

Stack ike Structures

9art =; Da$s and E$5ank$ents

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Earthquake Design 9rinci'le

:he criteria is; &inor /and frequent earthquakes should not

cause da$age

&oderate earthquakes should not cause

signicant structural da$age /5ut could haeso$e nonFstructural da$age

&aGor /and infrequent earthquakes should notcause colla'se

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Seis$ic Coe%cient &ethod


( )

( )2

aa

B h a

SZT

gV A T W W R

I

= =

?here4

Ah(Ta) - Design horiHontal accelerations'ectru$

W - Seis$ic ?eight

Design 5ase Shear;


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.unda$ental 8atural 9eriod /Cl676


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I$'ortance .actor /I

igher alue for $ore i$'ortantstructures6

:a5le < of 9art I of the code gies alues ofi$'ortance factor for 5uildings in :a5le


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one factor

alues of seismic zone factor ()in thecode are quite e$'irical 8ot 5ased on an( rational anal(sis of e,'ected

E9A and serice life6

one Area lia5le to shakingintensity

one.actor

II I /and lo?er 0610

III II 061

IK 06#27 Jan 2011


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Direction of round &otion /Cl6


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Direction of round &otion /Cl6


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Building Plans with Orthogonal Systems

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Building Plans with NonOrthogonal Systems

walls

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Direction of Earthquakeoading

During earthquake4 ground $oes in alldirectionsO the resultant direction changeseer( instant6

round $otion can resoled in t?o

horiHontal and one ertical direction6 Structure should 5e a5le to ?ithstand

ground $otion in an( direction :?o horiHontal co$'onents of ground

$otion tend to 5e co$'ara5le Sa(4 the e'icentre is to the north of a site6 round $otion at site in the northFsouth and

eastF?est directions ?ill still 5e co$'ara5le6

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Direction of oriHontal round &otion inDesign /Cl6


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Cl6


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8onFrthogonal S(ste$s /Cl6


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8onFrthogonal S(ste$s /Cl627 Jan 2011


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8onFrthogonal S(ste$s /Cl60M in 'lace of #0M6

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Cl661

In co$'le, structures such as a nuclearreactor 5uilding4 one $a( hae er(co$'le, structural s(ste$s6

8eed for considering earthquake $otion in

all three directions as 'er 100M*#0M rule6 8o?4 ET load $eans the follo?ing 2>

co$5inations; $l% 0.&$' 0.&$'z $l 0.&$'% 0.&$'z $lz 0.&$'% 0.&$'

ence4 E no? $eans 2> co$5inations A total of 7# load cases for RC structures@

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Cl662

In 'lace of 100M*#0M rule4 one $a( takefor design force resultants as 'er squareroot of su$ of squaresin the t?o /or4three directions of ground $otion

2)(2)(2)( ELzELyELxEL ++=

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Sit S i D i C it i


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Site S'ecic Design CriteriaCl660$I and

t U >0$t U "0$II and III

Irregular

Buildings

Regular

Building

Seis$ic

one

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h( D(na$ic Anal(sis3

E,'ressions for design load calculation /cl676=6# and load distri5ution ?ith height5ased on assu$'tions .unda$ental $ode do$inates the res'onse

&ass and stiness distri5ution are eenl(distri5uted ?ith 5uilding height h"s, gi*ing reg"lar mode sha!e

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h( D(na$ic Anal(sis3 /contdN

In tall 5uildings4 higher $odes can 5equite signicant6

In irregular 5uildings4 $ode sha'es $a(5e quite irregular

8ote that industrial 5uildings $a( haelarge s'ans4 large heights4 andconsidera5le irregularities;

:hese too ?ill require d(na$ic anal(sis6

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o?er Bound on Seis$ic .orce /Cl


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o?er Bound on Seis$ic .orce /Cl676!62

:his clause requires that in case d(na$icanal(sis gies lo?er design forces4 these5e scaled u' to the leel of forceso5tained 5ased on e$'irical a6 I$'lies that e$'irical ais $ore relia5le than

aco$'uted 5( d(na$ic anal(sis

:his is indeed the intention6

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o?er Bound on Seis$ic .orce /Cl6 76!62 /contdN

E$'irical e,'ressions for 'eriod Based on o5serations of actual asF5uilt

5uildings4 and hence

Are far $ore relia5le than 'eriod fro$ d(na$ic

anal(sis 5ased on questiona5le assu$'tions :hen4 ?h( d(na$ic anal(sis3

Een ?hen the results of d(na$ic anal(sisare scaled u' to design force 5ased one$'irical a; :he load distri5ution ?ith 5uilding height and

to dierent ele$ents is 5ased on d(na$ics6

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D(na$ic 9ara$eters V .orce

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&odal Co$5ination Cl


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&odal Co$5ination Cl676!6>6>

:his clause gies CTC $ethodrst and then si$'ler $ethod asan alternate6

CTC is a fairl( so'histicated$ethod for $odal co$5ination6 Itis a''lica5le 5oth ?hen the$odes are ?ellFse'arated and?hen the $odes are closel(Fs'aced6

&an( co$'uter 'rogra$$eshae CTC $ethod 5uilt in for$odal co$5ination6

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Alternate &ethod to CTC

Wse SRSS /Square Root of Su$ of Squaresif the natural $odes are not closel(Fs'aced6

Wse A5solute Su$ for closel(Fs'aced $odes

:o a''reciate the alternatie $ethod4consider t?o e,a$'les6

%%%%22

&

2

2

2

++++=

%%%&2 ++++=

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E,a$'le 1 on &odal


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E,a$'le 1 on &odalCo$5ination;

.or rst e $odes of i5ration4 natural'eriodL natural frequenc( and $a,i$u$res'onse are gien6 Esti$ate the$a,i$u$ res'onse for the structure6

1201=02#0#=01100

Res'onseTuantit(

"60"

761>

=600

26!

062006#=06"=8atural9eriod

=>#21&ode



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E,a$'le 1 on &odal Co$5ination /contdN

All natural frequencies dier fro$ eachother 5( $ore than 10M6 As 'er Cl6 #624 none of the $odes are closel(F

s'aced $odes6

As 'er section a in Cl6 76!6>6>4 ?e can useSquare Root of Su$ of Squares /SRSS$ethod to o5tain resultant res'onse as

*&)2$()+$()2&$()&+$()$$( 22222 =++++=


E,a$'le 2 on &odal


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E,a$'le 2 on &odalCo$5ination

.or rst si, $odes of i5ration4 natural'eriodL natural frequenc( and $a,i$u$res'onse are gien6 Esti$ate the$a,i$u$ res'onse for the structure6

!0"02001"02#0!=0Res'onseTuantit(

>600#6!=26">

16#=162!

160067!

06">

8atural 'eriod/sec

#21&ode



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E,a$'le 2 on &odal Co$5ination /contdN

As 'er Cl6 #624 $odes 2 and # are closed s'acedsince their natural frequencies are ?ithin 10M ofthe lo?er frequenc(6

Si$ilarl(4 $odes = and < are closel( s'aced6

Co$5ined res'onse of $odes 2 and # as 'ersection 5 in Cl676!6>6> - 2#0*1"0->20

Co$5ined res'onse of $odes = and < - "0 * !0- 170

Co$5ined res'onse of all the $odes as 'ersection a *,)-$()2$$()2$(),+$( 2222 =+++=

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Design and Detailing

As 'er the $athe$atical $odel structuresto 5e designed to ?ithstand againstloading6 /C

.ollo?ing criterias are to 5e $et

Strength

Sericea5ilit(

Sta5ilit(

Detailing; As 'er the assu$'tions ductilit( require$ent

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S'l6 conning


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Colu$n Detailing

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' greft6


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Bea$ Detailing

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Tns3

9lease feel free to Ask questions related to this lecture and

related to the sections of the code discussedherein

et $e kno? if so$e 'arts of this lecture ?erenot clear6

Documents

Lect 7 Seismic