wall struc
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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#
6:7 S:;S
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