Seismic Performance Evaluation of Hollow Concrete Block Infilled Reinforced Concrete Buildings in Case of Ethiopia
Daniel Dibaba Awayo
Key Words: Bare frame, infilled model, capacity curve, limit state capacities
1. INTRODUCTION Inmostmodernbuildings,thenon structuralcomponents account for 60 to 80 percent of the value of the building. HCBs are frequently used infill walls among the most commonly used masonry infills in Ethiopia. These infills participate in the lateral response of buildings and as a consequencealterthelateral stiffnessof buildings.Hence, naturalperiodsandmodesofoscillationofthebuildingare affectedinthepresenceofmasonryinfills.Theconventional designpracticeconsidersonlythemassesoftheinfillwalls withoutanattempttoincorporatetheirlateralstiffness.Asa result modeling the infill walls along with the frame elements is necessary to incorporate additional lateral stiffnessofferedbymasonryinfillwalls. Neglectingthesignificantinteractionbetweentheinfillwalls and building frames is the main reason why structural systems incorporating integrated infills panels react to strong earthquakes in a manner quite different from the expectedone.Therearemanydifferenttechniquesproposed in the literature for the simulation of the infilled frames, which can be basically divided in two groups, namely the micromodelsandthesimplifiedmacro models.Themicro modelsconsidersa highlevel ofdiscretizationof theinfill masonrypanel,inwhichthepanelisdividedintonumerous elementstotakeintoaccountthelocaleffectsindetail,while thesimplifiedmacro modelsaresupportedinsimplifications withtheobjectiveofrepresentingtheglobalbehaviorofthe infillpanelwithmainstructuralelements.
School of Civil Engineering & Architecture, Addis Ababa Science and Technology University, Ethiopia ***
Macro modeling is used to present accurate and realistic responseofinfillwallsanditusesequivalentdiagonalstruts tomodelthecontributionoftheinfillwallstotheresponse oftheinfilledframe.Thismethodreplacestheinfillpanelby two diagonal, compression only struts. This approach is advantageous since the masonry is a very heterogeneous materialanditishardtopredictthematerialpropertiesof the constituent members accurately. For the nonlinear analysis of large and complex structures under severe loadings,astheinducedbyearthquakes,inmanycasesitis not suitable to adopt refined models. Thus, many authors have in the last decades proposed and used simplified nonlinearmodelsforRCstructures.
ThemainfocusofthisresearchistostudytheeffectsofHCB infills on the seismic performance of RC buildings by implementing numerical models on the basis of finite elementprinciples.Threedistinctbuildingmodelcases(i.e. G+6, G+10 and G+15) each as a bare frame and distinctly having defined percentages of infill configuration are proposed for numerical analysis purpose. Bare RC frame buildingsareanalyzedanddesignedonETABS2016.2.1[1]. Analysisanddesign of the proposed building model cases followedtheconventionaldesignapproachasprescribedon thenewEthiopianBuildingsCodeStandards[2],[3]and[4]. While numerical modeling and nonlinear time history analysisofdesignedbuildingmodelcaseswiththeproposed infill configurations are computationally done on Seismo Struct [5] which is a fiber based finite element software package capable of predicting the large displacement behaviorofspaceframes.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page184
Abstract - Masonry infills are usually treated as non structural elements in buildings,andtheir interactionwith the bounding frame is often ignored in analysis and design of reinforced concrete structures. The main aimofthisstudyis to evaluate the seismic performance of HCB infilled reinforced concrete (RC) buildingsbyadoptingprobabilisticperformance assessment approaches. For the purpose of this study, three distinct buildings namely, seven story, eleven story and sixteen story, with typical floorplanwereproposedasthecase study. Each building cases are explicitly modeled as a bare frame and HCB in filled modelwithvaryingpercentageofinfill configurations. Bare RC frame buildings are analyzed and designed based on the conventional design approach on ETABS 2016.2.1, while numerical modeling and analysis of HCB in filled models are simulated on Seismo Struct 2016. Static pushover analysis and nonlinear dynamic time history analysis were adopted for performance evaluation of the case study buildings with respect to local and global parameters. Results of the study showed that increase in initial stiffness, strength, and energy dissipation of the infilled frame is considerable, compared to the bare frame. Inclusion of infills has showed a significant decrease in fundamental vibration period and story displacements. Also it was found that infills have significant contribution in arresting large lateral deflections and results in lower and most tolerable story displacements under excited earthquake motion.
Unreinforcedwallpanelsaretypicallyusedasinfillwallsin flexuralframedbuildings;structuralframeisfirstbuiltwith the masonry walls constructed later leaving some gaps between the framed members and the wall. In these applications,masonryisregardedasmasswithitsstiffness disregarded in the analyses and neither the frame nor the wallisdesignedfortheirpotentialinteraction.Whereout of plane loads dominate on these infill walls, they fail prematurely,potentiallyleavingtheframedstructure(where designedproperlyforseismicactioneffects)withminimal damage. Due to the high stiffness, the wall will generate higherseismicforcesforwhichthebuildingwouldnothave been designed, causing significant damage to framed structureswithpotentialforcollapseofthewholebuilding. Severalfailuresarereportedintheliteratureascasestudies andtheoreticalanalyses[6]. Inmanyearthquake pronecountries,aconcretepanelinfillis reinforced with a masonry panel. Although the infill panel significantlyincreasesthestiffnessandstrengthoftheframe, itscontributionisoftenoverlookedduetolackofknowledge incompositebehavioroftheframeanditsinfillpanel[7]. Limiteddataexistonthedynamicpropertiesofmasonrywall infilledframes,sinceveryfewshake tableexperimentsare performed on masonry infilled structures. Fardis et al. [8] reported on the shake table test performed on single bay two story RC frames with eccentric (asymmetric in plan) masonry infill walls subjected to bidirectional ground accelerations.
Consideringthesimplemodelusedwithasinglestrutforthe URMinfillwall,theOpenSeessimulationresultsareingood agreement with the experimental results. From the above rigorousstudytheresultshowedthattheURMinfillwallhad a significant role in the strength and ductility of the test structure and should be considered in both analysis and design.
2.2. Failure Modes of Infilled RC Frames
Thefailuremechanismsofthemasonryinfilledframesare complexbecauseofthehighnumberofparametersinvolved intheseismicresponseofthestructuresuchasthematerial property,configuration,andrelativestiffnessoftheframeto the infill, detailing, etc. Experimental results show that masonryinfilledframescanexperienceawidevarietyofthe failuremodes.
It is worth mentioning that only the first two modes, the CornerCrushing(CC)andtheSlidingShear(SS)modes,areof practical importance since the third mode Diagonal Compression (DC) occurs very rarely and requires a high slenderness ratio of the infill to result in out of plane bucklingoftheinfillunderin planeloading.Thisishardlythe casewhenpracticalpaneldimensionsareused,andthepanel thicknessisdesignedtosatisfytheacousticisolationandfire protection requirements [10]. The fourth mode Diagonal Cracking(DK)shouldnotbeconsideredafailuremode,due to the fact that the infill can still carry more loads after it cracks.AlthoughthefifthmodeFrameFailure(FF)mightbe worth considering in the case of reinforced concrete (RC) frames, when it comes to steel frames infilled with unreinforced hollow concrete masonry blocks, this mode hardly occurs. The study conducted herein models the CC mode only, which is the most common mode of failure. In ordertodeterminethegoverningfailuremode,thecapacity
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page185 2. LITERATURE REVIEW 2.1. Behavior of Masonry Infilled Reinforced Concrete Frames
Fig-1: Comparisonsbetweentheexperimentaland simulatedresults[9].(a)Partialtimehistoriesand(b)peak response
Multi storyreinforcedconcretebuildingsforapartmentuse (condominiums),andthreebuildingmodelshavingdifferent numberofstory:seven story(G+6),eleven story(G+10),and sixteen story(G+15)withsimilarfloorplansandfunctions areusedinthispaper.Themainpurposeofhavingvarying storyasthecasestudyistoinvestigatetheeffectofinfillsas thestoryheightincreases.Asthispaperismainlyfocusedon seismic performance evaluation of HCB infilled reinforced concrete buildings, it would give better understanding on howtheinfilleffectsaltertheperformanceofthedesigned structuresasthebuildinggethigherinstorylevel.
3.3. Macro Modelling of Infill Walls Macro modeling is used to present accurate and realistic responseofinfillwallsanditusesequivalentdiagonalstruts tomodelthecontributionoftheinfillwallstotheresponseof the infilled frame. This method replaces the infill panel by twodiagonal,compression onlystruts.Theadoptedmodel assumesthatthecontributionofthemasonryinfillpanelto the response of the infilled frame can be modeled by replacing the panel by a system of two diagonal masonry compression struts. The individual masonry struts are consideredtobeineffectiveintension
All building models are proposed to be situated at Addis Ababawherethecurrentbuildingcodeclassifiedasseismic zoneIII.Afterpreparinggeneralarchitecturalplansforthe proposed building models, analysis and seismic design of frameelementsareperformedaccordingtonewEthiopian BuildingsCodeStandards(ESEN:2015).Thedesignprocess comprisedpreparingabasicstructuralanalysismodelofthe building with the dimensions and details obtained from preliminary design strategies. Then apply design lateral studyelevationbuildingfollowedtheanalysis.elementsforces,performstructuralanalysis,andthendesignstructuralbasedonstressresultantsobtainedfromstructuralSeismicactionisusedasgoverninglateralforceonbuildingstructuresandtheanalysisforthelateralactionmodalresponsespectrummethod.Theproposedmodelsareclassifiedasregularbothinplanandthattheparametersandresultsoftheintendedcouldeasilybeinterpretedinrelationtoinfillwalls.
3. METHODOLOGY
Table 1: Strutwidthandcoefficientbyvariousresearchers [13]
2.3. Models for the Infill Panels Inmodellingofinfillpanelstheproblemreliesonidentifying a reliable and simple model which could represent the masonry infill. Many difficulties were due to the intrinsic characteristicsofmasonry.Asitisanon homogeneousand anisotropic material, it is difficult to find a generally valid constitutivelaw.Furthermorethemasonryshowssignificant degradation of stiffness and strength under cyclic loading. Theresultshowedthattheratiooftheestimatedequivalent strutwidthtothediagonallengthofinfill(w/dinf)areranging between about 0.1 to 0.33 except the result calculated by usingStaffordSmithandCarter[12]methodequationwhich generatelargevaluefortheequivalentstrutwidth.
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page186 oftheinfillpanelsobtainedbytheproposedmethodshould becomparedtothecapacityundertheSSmode,whichmay be estimated using the method suggested by Paulay and Priestley[11].
Accordingly,infillpanelsaremodeledbyequivalentdiagonal struts,whichcarryloadsonlyincompression.Theshearstrut model,representingtheinfillpanelsshearcapacitynormalto thegravitationaldirectionisimplementedinanequivalent discreteshear typemodel.Intheproposedinfillpanelmodel, each masonry panel is structurally defined by considering four support strut elements, with rigid behavior, and a central strut element, where the nonlinear hysteretic behaviorisconcentrated.Theforcesdevelopedinthecentral elementarepurelyoftensileorcompressivenature.Besides it is possible to obtain mechanical properties of the infill wallsfromprismteststomodeltheequivalentstruts,inthis paper test machines used to determine the mechanical propertiesofthemasonryprismsarenotavailablethatmost prevalentvaluesofcompressiveandshearstrengthsofHCB masonryprismswerebrowsedfromrelevantliteraturesand code conforming values are thus used as input data for
3.2. Seismic Design of RC Buildings
3.1. Introduction Reinforced Concrete frame structures are constructed initially due to ease of construction and rapid work in progress.Masonryinfilledwallsaremostcommonbuilding elementfoundthroughouttheworld.Infilledframemaybe definedascombinationofmomentresistingplaneframeand infillwall.Structuralengineers,duringthedesignprocessofa building,typically,ignoretheeffectsofinfillmasonrywallsin the structural analysis. The only contributions of masonry infill walls are their masses as non structural elements. Consequently, analyses of the structures are based on the bareframes.Inthelast4decades,theeffectsofinfillwallsin framestructureshavebeenextensivelystudied.Experimental and analytical study results show that infill walls have a significant effect on both the stiffness and the strength of structures.
The investigated buildings are a multi story reinforced concretebuildingsforapartmentuse(condominiums),and three building models having different number of story: seven story (G+6), eleven story (G+10), and sixteen story (G+15)withsimilarfloorplansandfunctionsareusedforthe study.Seismicactionisusedasgoverninglateralforceonthe building structures and the analysis for the lateral action followed modal response spectrum method. The proposed building models are classified as regular both in plan and elevation that the parameters and results of the intended studycouldeasilybeinterpretedinrelationtoHCBwalls.All analysesanddesignsareperformedonETABS2016software (CSI 2016. ETABS. Integrated Building Design Software, Computers and Structures Inc. Berkeley). A three dimensional(spatial)structuralmodelisusedforallcases. Themodelcasesaremultistoryreinforcedconcretebuildings composed of frame system and solid slab floors. Beams, supportingfloorsandcolumnsarecontinuousandmeetat nodes, often called “rigid” joints. Such frames can readily carry gravityloads while providingadequate resistanceto horizontalforces,actinginanydirection.
numericalmodelingofinfilledRCframesonfiniteelement softwarepackages. Fig 2: Structurallayoutofbareframe,infilledframeand infillframemodels
Fig 4: Equivalentshearspringmodel
4.1. Analysis Approach
Fig 3: Equivalentdiagonalstrutmodel
The proposed building model cases with various infill configurations are thus numerically modelled on SeismoStruct 2016. This computer program is analytical softwareworksonprinciples offiniteelementpackagefor structural analysis, capable of predicting the large displacement behavior of space frames under static or dynamic loadings, taking in to account both geometric nonlinearities and material inelasticity. The software has inbuilt nonlinear and hysteretic material properties for concrete,steel,infillsandotherengineeringmaterials.Five (5) infill configuration models are proposed for each designedbuildingsmodelcasestouseinnumericalmodeling andassessmentofseismicperformances. All the proposed building models having infill panels are introducedwith20cmthickHCBasexternalwalland15cm thick as internal walls. Also the effect of openings due to windowsand doorshas been considered through stiffness reductionfactor.Staticpushoverandnonlineartime history analysisare performed after complete numerical model of buildingsintheirthreedimensionalstate. 3.4. Seismic Performance Evaluation
Inthispaper,pushoverandnonlineardynamictimehistory analyses are performed on SeismoStruct 2016software to evaluatetheseismicperformanceofthecasestudybuildings. Topredicttheresponseoftheselectedstructuresduringan earthquake, 30 artificial accelerograms using SeismoArtif 2016 are generated, scaled, and matched with Ethiopian responsespectrumandloadedonallbuildingmodelcasesfor nonlineardynamictimehistoryanalysis.
The structure is modeled, analyzed, and designed in computersoftware“ETABS2016.2.1.Beamsandcolumnsare modeled with line or frame elements, shear walls are modeled with wall elements, and slabs and roof floors are modeled with area elements. Analysis and design of slabs entirely followed coefficient method where the approach dependsuponwhetheritisaone wayortwo wayslab, supportconditionsandtheloadings.Accordingly,slabsare analyzed on spread sheets/excel sheets based on their support conditions and corresponding parameters as per EBCS.Thecalculatedpartitionloads,floorfinishes,andlive loads are then assigned on the modeled area elements on ETABS2016.2.1soastoconsiderfortheirrespectiveapplied gravityloads.
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4. ANALYSIS AND DESIGN OF REINFORCED CONCRETE BUILDINGS
Fig 5: (a)3DsimulatedG+6bareframebuildingmodel, (b)3DsimulatedG+6infilledframebuildingmodel
6.
Fig 7: (a)3DsimulatedG+15bareframebuildingmodel, (b)3DsimulatedG+15infilledframebuildingmodel
Fig 6: (a)3DsimulatedG+10bareframebuildingmodel, (b)3DsimulatedG+10infilledframebuildingmodel
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Fig 8: Computersusedtorunnonlineardynamictime historyanalysis RESULTS AND DISCUSSION 6.1. Base Shear Itwasobservedthatseismicbaseshearforinfilledbuilding modelsaregreaterthanbareframebuildingmodel.Butthe baseshearofinfilledmodelsdecreasedabruptlytoavalueof about 1,000kN just after infill onset cracks where their stiffness contribution starts to degrade. Then the gradual applicationofincrementalloadcallsuponframeelements resistanceandthusthebaseshearwouldstarttoincrease.
The inclusion of infills has shown appreciable increase in seismic base shear at immediate occupancy (IO) performance level. 25% infill introduction in bare frame modelhasraisedtheseismicbaseshearto6,117.80kN(39% increase), 7,488.30kN (65.9% increase) and 11,099.24 (132%increase)forG+6,G+10andG+15buildingmodels respectively.Accordingly,100%infill introductionin bare frame model has raised the seismic base shear to 14,307.30kN (224% increase), 17,363.80kN (284.7% increase)and23,519.43(392%increase)forG+6,G+10and G+15buildingmodelsrespectively. Generally it has been noticed that additions of infills have relativelylargereffectasthenumberofstoryincreases.Asit has been seen the percentage deviations of seismic base shears for G+10 building models are greater than the correspondingvaluesG+6buildingmodel,andsimilarlythat ofG+15buildingmodelsaregreaterthanthecorresponding valueG+10buildingmodels.
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Table 2: SeismicbaseshearatIOperformancelevelfor G+6buildingmodels
Fig 9: StorydisplacementsofG+6buildingmodelcases underTH 2groundmotion
Fig 11: StorydisplacementsofG+6buildingmodelcases underTH 7groundmotion Under simulated ground motions the bare frame model displacedinlargelycomparedtotheinfilledmodels.Itwas foundthattheroofdisplacementsofbareframemodelsare 137,205,and223mmunderTH 2,TH 5andTH 7ground motionsrespectively.Ontheotherhandintroductionof25% infillsintothebareframemodelhasconsiderablyreduced theroofdisplacementsto46,92,and110mmunderTH 2, TH 5andTH 7groundmotionrespectively.Furtherinclusion ofinfillshasreducedtheroofdisplacementstoappreciable value.
Table 4: SeismicbaseshearatIOperformancelevelfor G+15buildingmodels
6.2. Story Displacements Seismic performance evaluation is directly related to displacementordeformationandthusestimationofseismic deformationdemandisaprimaryorfundamentalconcernin performance evaluation of reinforced concrete structures under seismic excitation. The basic analysis approach consists of performing nonlinear dynamic time history analysisforagivenstructureandgroundmotion,usingthree dimensional nonlinear analysis on SeismoStruct software. The story displacement of the case study building models were studied under randomly selected individual ground motions.Accordinglyoutofemployed30groundmotionsset in the dynamic analysis, 3 (three) ground motions were considered for evaluation of building performance with respecttostorydisplacements. G+6 Building Model Cases
Table-3: SeismicbaseshearatIOperformancelevelfor G+10buildingmodels
Fig 10: StorydisplacementsofG+6buildingmodelcases underTH 5groundmotion
Fig 17: StorydisplacementsofG+10buildingmodelcases underTH 7groundmotion
Under simulated ground motions the bare frame model displacedinlargelycomparedtotheinfilledmodels.Itwas foundthattheroofdisplacementsofbareframemodelsare 112,172,and192mmunderTH 2,TH 5andTH 7ground motionsrespectively.Ontheotherhandintroductionof25% infillsintothebareframemodelhasconsiderablyreduced theroofdisplacementsto45,118,and138mmunderTH 2, TH 5andTH 7groundmotionrespectively.Furtherinclusion ofinfillshasreducedtheroofdisplacementstoappreciable value G+15 Building Model Cases
Fig 16: StorydisplacementsofG+10buildingmodelcases underTH 5groundmotion
Fig 15: StorydisplacementsofG+10buildingmodelcases underTH 2groundmotion
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Under simulated ground motions the bare frame model displacedinlargelycomparedtotheinfilledmodels.Itwas foundthattheroofdisplacementsofbareframemodelsare 95, 127, and 149 mm under TH 2, TH 5 and TH 7 ground motionsrespectively.Ontheotherhandintroductionof25% infillsintothebareframemodelhasconsiderablyreduced theroofdisplacementsto79,105,and128mmunderground motionrespectively.Furtherinclusionofinfillshasreduced theroofdisplacementstoappreciablevalue. From the investigation of story displacements under the simulated ground motions it was noted that the effect of infills in reducing the story displacements is considerable. Building models with large infills have lesser story displacementsandperformwellunderseismicexcitations.
Fig 12: StorydisplacementsofG+10buildingmodelcases underTH 2groundmotion
Fig 13: StorydisplacementsofG+10buildingmodelcases underTH 5groundmotion
Fig 14: StorydisplacementsofG+10buildingmodelcases underTH 7groundmotion
Thecontributionsofinfillsincreaseasthenumberofstories increase and the monitored story displacements wouldbe thus lesser compared with low rise buildings. Thus infills haveasignificantcontributioninarrestinglargelateralstory displacementssincetheirstiffnessareparticipatinginlateral loadresistingsystemforexternallyappliedlateralloads.
G+15 Building Model Cases
Fig 20: Inter storydriftratioofG+15buildingmodelcases (a)underTH 2groundmotionand(b)underTH 5ground motion Inter storydriftforthebuildingmodelcasesunderrandomly selected ground motions were studied and the results showedthatbuildingmodelswithinfill wallshavesmaller inter storydriftandthisvaluedecreasedappreciablyabove secondstory. Since the ground and first floors have larger floordisplacement ascompared toother floors theirstory drift is somehow grater that the floors above. Bare frame building models have a higher story drift and inclusion of infillsintothemhassubstantiallyreducedthestorydriftsto appreciablevalue.Theeffectofinfillsisthusconsiderablein
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6.3. Inter-Story Drift Lateraldeflectionisthepredictedmovementofastructure underlateralloads;andstorydriftisdefinedasthedifference inlateraldeflectionbetweentwoadjacentstories. Duringan earthquake,largelateralforcescanbeimposedonstructures and it requires that the designer assess the effects of this deformationonbothstructuralandnonstructuralelements. Ithasbeenrecognizedthattheinter storydriftperformance ofamultistorybuildingisanimportantmeasureofstructural and non structural damage of the building under various levelsofearthquakemotion
G+6 Building Model Cases
G+10 Building Model Cases
Fig 19: Inter storydriftratioofG+10buildingmodelcases (a)underTH 2groundmotionand(b)underTH 5ground motion
Fig 18: Inter storydriftratioofG+6buildingmodelcases (a)underTH 2groundmotionand(b)underTH 5ground motion
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page192 limiting subjectedthestorydriftsexperiencedinthebuildingstructurestoseismicexcitation. 7. CONCLUSIONS Theinclusionofinfillshasshownappreciableincrease in seismic base shear at immediate occupancy performancelevel.25%infillintroductioninbareframe modelhasraisedtheseismicbaseshearto6,117.80kN (39% increase), 7,488.30kN (65.9% increase) and 11,099.24 (132% increase) for G+6, G+10 and G+15 buildingmodelsrespectively. Inclusionof respectively.underreducedinfirespectively.223displacementsappreciableinfillshasreducedtheroofdisplacementstovalue.Itwasfoundthattheroofofbareframemodelsare137,205,andmmunderTH2,TH5andTH7groundmotionsOntheotherhandintroductionof25%llsintothebareframemodelhasconsiderablytheroofdisplacementsto46,92,and110mmTH2,TH5andTH7groundmotions Bare frame building models have a higher story drift varyinginbetween(0.167 0.697)%underTH 2ground motion and in between (0.333 1.12) % under TH 5 groundmotion.Buttheinclusionofinfillsintotheframe elementshas substantiallyreducedthestory driftsto oscillate in the range (0 0.13) % above second floors andabout0.63%uptosecondfloors.Theeffectofinfills is thus considerable in limiting the story drift experienced in the building structures subjected to seismicexcitation. 8. REFERANCES [1] ETABS 2016 V16.2.1 [CSI ETABS 2016], “Integrated Building Design Software, Computers and Structures Inc. Berkeley,” (online), available from [2]http://www.downloadly.ir.ESEN[1991:2015]EthiopianStandardsBasedonEuro Norms “Actions on Structures Part 1 1: General Actions Densities, Self weights, Imposed Loads for Buildings” MinistryofConstruction,AddisAbaba,Ethiopia.
[8] Fardis, M.N. and Negro P. [2006] “SPEAR Seismic performance assessment and rehabilitation of existing buildings”,ProceedingsoftheInternationalWorkshoponthe SPEARProject,Ispra,Italy.
[10]ComiteEuro InternationalDuBeton,[1996]‘‘RCframes under earthquake loading.’’ State of the Art Rep., Tomas TelfordServices,Ltd.,London.
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[11] Paulay T., Priestley M.J.N. [1992], Seismic Design of Reinforced Concrete and Masonry Buildings, John Wiley & SonsInc.,NewYork.
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[12] B. Stafford Smith and C. Carter. [1969] “A method of AnalysisforInfillFrames,”ProceedingsoftheInstitutionof CivilEngineers,Vol.44,pp.31 48.
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