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Design of RC Wall Structures in Seismic Zones. Comparisonbetween Romanian and European Codes

Radu Pascu, Mihai Munteanu, Chair of Reinforced Concrete Buildings,Technical University of Civil Engineering Bucharest

. !ntroduction

Eurocode 8, published in 1994 as a Europeanprestandard, is considered to represent the latestord in codified earth!ua"e design# $n theother hand, in Ro%ania there is a large practicale&perience in seis%ic design and the Ro%anianseis%ic design codes ere recently revised'199( and 199)*, including the latest e&perienceand concepts in seis%ic design#

Both Ro%anian a European Codes are based onthe capacity %ethod# +oever, in practice thereare so%e differences beteen the to Codes#The purpose of this co%parative study is to

point out ho these differences are reflected inthe case of reinforced concrete all structures#This co%parative study is also intended to be acase study for the preparation of the neversion of Ro%anian design codes#

typical %ultistory all structure as chosento illustrate the co%parison# To differentdesign variants are perfor%ed, the firstaccording to Ro%anian seis%ic codes 'na%ed

belo -1..*, and the second according toEuropean codes 'na%ed belo EC8*#The %ain geo%etry of the analysed structure isin accordance ith a pro/ect designed by0-roiect Bucuresti 2esign 3nstitute and is

representative for Bucharest, because there erethousands of flats built according to this pro/ect

beteen 198. and 1989#

". Case Stud# Description

The eightstory reinforced concrete dual syste%apart%ent bloc" is in accordance to the 5211f5

pro/ect designed by 5-roiect Bucuresti5 2esign3nstitute 61.7# 3t is a structure typical for the0cellular type, ith structural alls beteen theapart%ents and fra%es beteen the alls 'seefigure 1*#

The building has three spans of #4., #1. and#). %# in the transverse direction and seven

bays ranging fro% #. to 4#. %# in thelongitudinal direction# The area of the currentfloor is #. %(# The story height is (#: %# forall levels# The floor is a 1(. %% thic" RC slab#The peri%etral alls are of lighteight concrete

bloc"s %asonry# The partitioning alls areprecast lighteight concrete units#

The geo%etrical di%ensions of the alls fro%pro/ect 211f ere "ept unchanged, hile designaction effects and reinforce%ent details erederived according to 6)7 and respectively 697#The design of four structural alls as fullydetailed# The %ain para%eters of the to designvariants are su%%arised in table 1#

$. %asic !nput Data

$. Ductility Classes and Behaviour Factors

;or the EC8 variant, the %ediu% ductility class0


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q = qokDkRkW1,5 (1)

The basic value qo= 5 for all structures ithcoupled alls, kD = 0,75 for 2C9(

for all structures is = 0,25# This is

e!uivalent ithq = 1/= 4#

$." Design Spectra

a* b*

Figure 1.Eig!-"!orie" #u$l w$ll-equi%$le&! "'"!e $) urre&! *loor +l$& ) er!i.$l "e.!io&

Table 1. Main parameters of the design variants for the wall structure

&ariant Ductilit#class

Spectrum %eha'iourfactor

Design actioneffects

Section 'erificationand detailing

Eurocode 8 %ediu% 0


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The structure as designed for the seis%icintensity corresponding to Bucharest, accordingto the Ro%anian code 687, hich provides aground acceleration of .#(g# The elasticresponse spectra corresponding to the tovariants resulted as in figure (a# 3n the @one

corresponding to the %ain vibration periods, theRo%anian spectru% gives an acceleration valueabout 1.A higher then the EC 8 spectru%#

The nor%ali@ed design spectra for the tovariants are given in figure (b# 3n the rangecorresponding to the %ain vibration periods, theRo%anian spectru% gives an acceleration valueabout 4A higher then the EC 8 spectru%,

because the behaviour factors are different '#:

for EC 8 and 1>? 1>.#( ? 4 for -1..9(*#

$.$ Combination of ctions in the SeismicDesign Situation

The %asses are slightly greater in the -1..variant, because the fractions of the occupancyand sno loads are greater than in the othervariant# The values of the variable actions and ofthe co%bination coefficients in the to variantsare given in table (#

$.( Materials

-8>9) allos the use of concrete class higherthan Bc1 'C1(>1*, hile in EC8, the loest

class alloed for 2C(# +ence echose concrete class C (.>(#

;or the %ain reinforce%ent, steel 4.. aschosen, hile for stirrups ((. as used# Theresistence of 4.. corresponds to Ro%anian -C

). steel, and that of ((. to $B :#

$.) Modelling and Methods of nalysis

spatial %odel and a %ulti%odal analysis ereperfor%ed for both variants# This type ofanalysis as co%pulsory only in the EC 8variant, because the structure is classified asirregular in plan# 3n the other variant, asi%plified plane %odel could also be used# Theefforts ere obtained by the R %ethod, by

superposition of the first nine %odes#

The design seis%ic forces ere only slightlygreater in the -1.. variant, because thedifferences in elastic response accelerations,reduction factors and %asses partiallyco%pensated# This resulted in si%ilar %o%entsand shear forces in the alls 'figure 4*# &ialforces in alls and shear forces in coupling

bea%s are different, because the stiffness of thecoupling bea%s results loer in the -1..

variant#

3n fact, EC 8 recco%ands the use of theuncrac"ed stiffness, but per%its also todifferentiate the stifness to account for possibledifferences of their crac"ed state 'clauses #1#'*

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5 4

Vibration period (sec)

Elasticresponseacceleration(m/s2)

EC 8 elastic response spectrum

for C type soilP100-92 elastic response

spectrum for Bucarest

1!0.32 sec "torsion#

2 ! 0.28 sec "trans$ersal#

3!0.24 sec "lon%itu&inal#

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 0.5 1 1.5 2 2.5 3 3.5 4

Vibration period (sec)

Normalizedacceleration

EC 8 &esi%n response spectrum

for C type soilP100-92 &esi%n response

spectrum for Bucarest

1!0.32 sec "torsion#

2 ! 0.28 sec "trans$ersal#

3!0.24 sec "lon%itu&inal#

a* b*

Figure 2 $) El$"!i. re"+o&"e "+e.!r$ ) or$lie# #e"ig& "+e.!r$

Table !. "ariable loads# characteristic values and combination coefficients

*oad EC + P

t#pe -/01m"2 " -/01m"2 nd

$ccupancy (#.. .# 1#. .#4

no 1#.. . 1#.. .#4


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of -art 1( and (#11#1#(#'1* of -art 1*# -8>9)'#4#(* recco%ands to ta"e into account thecrac"ed state, by reducing the stiffness of thealls ith about .A and that of the coupling

bea%s ith a fraction depending %ainly of theiraspect ratio# ;or e&a%ple, in the case of

ordinary buildings as that in the or"ede&a%ple, the reduced stifness is=

le r r

r

r

, ,, ,= +

=0 2 1 1 52

= +

=0 2 1 1 5 0 35

2

, , ,, ,

l

r

r

r

r(4)

here e,r and ,r are respectively the crac"ed

and the uncrac"ed %o%ent of inertia of thecoupling bea% section, and r and lr are thedepth and the span of the bea%#s a conse!uence, the ratio of the all andcoupling bea% stifness changes as follos=

e (

e r

(

r

(

r

,

,

,

,

,

,

,

,= =

0 7

0 35 2

(5)

here e,r and ,r are respectively the crac"ed

and the uncrac"ed %o%ent of inertia of the allsection#

3t is also to be noted that the active flange idthof the all sections in the to variants resultsdifferent# +oever, the differences are not veryi%portant and %ay be 0covered by the

possibility of action effects redistribution hichallods redistributions in the range of (. to .

A of the action effects resulted fro% analysis'clause (#11#1#('* in -art 1 of EC 8 and#4#( in -8>9)*#

$.3 Design Criteria

3n EC 8, the design criteria for concretestructures are included in chapter (#4 of -art 1# They e&press the i%ple%entation of thedesign concepts described in -art 11 and in

(#1# of -art 1#

3n the Ro%anian codes, the general concepts aredescribed in chapter ( of -1..>9( and theirapplication in the case of all structures inchapter of -8>9)#

ccording to both Ro%anian and EuropeanCodes, the %ain criteria are=

e re"i"!$&.e .ri!erio&= all critical regions ofthe structure shall have a resistance ade!uatly

higher than the corresponding action effectsoccuring under the seis%ic design situation

0

1

2

3

4

5

6

'

8

-50 0 50 100 150 200 250 300 350 400

Wall bending moment (kNm x 10-1)

Leel

P100-92

EC 8

0

1

2

3

4

5

6

'

8

0 10 20 30 40 50

Wall s!ear "orce (kN x 10 -1)

Leel

P100-92

EC 8

0

1

2

3

4

5

6

'

8

0 50 100 150 200 250 300

#xial "orce (kN x 10-1)

Leel

(%)(s EC 8

(%-(s EC 8

(%)(s P100

(%-(s P100

0

1

2

3

4

5

6

'

8

0 2 4 6 8 10 12 14 16

$o%pling bea ms s!ear "orces (kN x 10-1)

Leel

P100-92

EC 8

Figure 3 .!io& e**e.!" *ro $&$l'"i" i& w$ll $xi" e!wee& 6 $


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for C4.>., here *.# is the co%pressivestrenght of the concrete# Fo difference is %adefor the concrete in the critical @one 'na%ed @one in -8* and outside the critical @one 'na%ed@one B in -8*#

3n EC 8, the resistance of the concrete outsidethe critical @one is (A greater than in thecritical @one# ;or the critical @one, the concreteresistance is=

R#2= 0,4(0,7 - *.k/200)*.#wo (7)

here 0,lwis the internal lever ar%#Considering the cases of C(.>( and respectivlyof C4.>. concrete, R#2 is 0,182wolw*.# and0,1wolw*.##

3t is obvious that -8 is conservative '((A inco%parison to EC8*#

3t is also to be noted that EC 8 'in fact EC (*provides a reduction of the resistance R#2 if aco%pressive force acts on the ele%ent# Thisreduction beco%es effective only if the average

co%pression stress .+,e** is greater than 0,4*.#,hich does not generally occur in the case ofstructural alls=

R#2,re#= 1,7R#2(1-.+,e**/*.#) R#2

1,7(1-.+,e**/*.#) 1

.+,e**/*.#0,4 ()

Di$go&$l !e&"io& *$ilure#Both -8 and EC8 provide a verification of thefolloing type=

9#R#3= .#: w# (8)

here 9#is the design shear force and .# andw#are the contributions of the concrete and ofthe hori@ontal reinforce%ent to the shearresistance#

3n EC8, the contribution of the hori@ontalreinforce%ent is deter%ined in different ays,

depending on the shear ratio " = ;9#/(9#lw)#

+oever, for "< 2and ( G "


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Both 6)7 and 697 re!uire a %ini%u% ebthic"ness wo = 150 and a 0vertical

slenderness condition wo "/20# ;or usualinhabitation buildings in Ro%ania, the latterdoes not operate, because "= 275 and "/20= 137,5 A 150 #

EC8 6)7 provides also a 0hori@ontal slenderness

condition woqlw/0, not ta"eing into accountthe favourable effect of boundary ele%ents andflanges# s lw is fre!uenly beteen 4 and ,this gives %ini%u% all thic"ness beteen 250and375 #

(.) Specific Measures and Detailing ofStructural &alls

The reinforce%ent in the critical @one of the allin a&is ) is given in ;igure #

The longitudinal reinforce%ent as generallygoverned by the %ini%u% reinforce%entre!uire%ents# Ieb reinforce%ent resulted largerin the EC8 variant, na%ely in the hori@ontaldirection ';igure )*#

80

143

1'8

0 50 100 150 200

,EC/ E(

/

,EC/ EB

E(CEE(

7(/ EB

E(CEE(

Figure R$!io o* e**e.!i%e rei&*or.ee&! i& !e w$ll$"e "e.!io& (E/B100 C)

The length of the confined end @one resultedfro% the %ini%u% re!uire%ents '1.A of thelength of the all cross section in the -1..

variant and 1A in the EC8 variant*#

a* -1.. variant b* EC8 variant

Figure 5 Rei&*or.ee&! o* w$ll i& $xi" $! !e $"e "e.!io&


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(.3 "erification and Detailing of Coupling$lements

Figure 7 Rei&*or.ee&! o* .ou+li&g e$" $! le%el" 2 !o5 E %$ri$&!

Figure Rei&*or.ee&! o* .ou+li&g e$" $! le%el" 2 !o5 B100 %$ri$&!

156

68

140

'1

0 50 100 150 200

(9:(/

/(;,E;/

le$els 6-8

le$els 2-5

Figure 8 R$!io o* e**e.!i%e rei&*or.ee&! i& .ou+li&ge$" (E/ B100 C)

3n the EC8 case, bidiagonal reinforce%ent asneeded at the levels ( to 'figure :*, andorthogonal reinforce%ent as used for the otherlevels# 3n the -1.. case 'figure 8*, orthogonalreinforce%ent as used for all levels, because

bidiagonal reinforce%ent is alloed only if theall thic"ness e&ceeds (. %%#

3n general, longitudinal reinforce%ent resultedhigher in the EC8 case, due to the %ini%u%reinforce%ent re!uire%ents# +oever, transverse reinforce%ent resulted loer, because for2C


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The co%parison beteen Ro%anian andEuropean seis%ic codes shall be developedthrough %ore case studies, covering a iderrange of all structure buildings#

Design of RC Wall Structures in Seismic Zones.Comparison between Romanian and European Codes

Summar#

This paper is a co%parative study beteen the designprovisions for RC all structures in seis%ic @ones inEurocode 8 and in the Ro%anian Codes of -ractice# BothRo%anian and European Codes are based on the capacitydesign procedure# +oever, so%e differences appearhen these principles are applied, and they areillustrated in this paper by the case study of an eight story reinforced concrete all structure# ;inally, so%econclusions concerning the design of %ultistorey

reinforced concrete all structures in seis%ic @ones aredran#

Calcul des structures 4 murs de contre'entement enb5ton arm5 en 6ones sismi7ues. Comparaison entreles r5gles roumaines et 5urop5enes

R5sum5

Ce travail est une Ktude co%parative entre les rKglesKuropKenes et les rKgles rou%aines concernant le calculdes structures L %urs de contrevente%ent en bKton ar%K

en @ones sis%i!ues# Jes rKgles rou%aines et cellesKuropKenes sont basKes, toutes les deu&, sur la %Kthodedes capacitKs# Toutefois, il y des diffKrences !uiapparaissent lors de lapplication de ces %M%esprincipes, et elles sont illustrKes par lKtude dunestructure L huit Ktages avec des %urs de contrevente%enten bKton ar%K# ;inale%ent, lKtude aboutit L certainesconclusions concernant le calcul en @ones sis%i!ues desstructures L %urs de contrevente%ent en bKton ar%K#

References

617 E0& 889 /88(2Euro.o#e 1 6$"i" o* De"ig&

$ .!io&" o& 9!ru.!ure"-B$r! 1 6$"i" o* De"ig& #European -restandard#

6(7 E0& 889"9 /88(2Euro.o#e 1 6$"i" o* De"ig&$ .!io&" o& 9!ru.!ure"-B$r! 2-1 De&"i!ie", 9el*-weig! $ +o"e# o$#"# European -restandard#

67E0& 88"99 /882Euro.o#e 2De"ig& o* o&-.re!e 9!ru.!ure"-B$r! 1 e&er$l Rule" $ Rule"

*or 6uil#i&g" # European -restandard#

647 E0& 88+99 /88(2Euro.o#e De"ig& +ro%i-"io&" *or e$r!qu$ke re"i"!$&.e o* "!ru.!ure" - B$r!1-1 e&er$l rule" - 9ei"i. $.!io&" $ ge&er$lrequiree&!" *or "!ru.!ure"European -restandard#

67 E0& 88+99" /88(2Euro.o#e De"ig& +ro%i-"io&" *or e$r!qu$ke re"i"!$&.e o* "!ru.!ure" - B$r!1-2 e&er$l rule" - e&er$l rule" *or uil#i&g"European -restandard#

6)7 E0& 88+99$ /88(2Euro.o#e De"ig& +ro%i-"io&" *or e$r!qu$ke re"i"!$&.e o* "!ru.!ure" - B$r!

1-3 e&er$l rule" - 9+e.i*i. rule" *or %$riou"$!eri$l" $ elee&!"European -restandard#

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