Shear Wall & Dome

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  See discussions, stats, and author profiles for this publication at: Seismic Vulnerability of RC Shear Wall Buildingwith a Dome Roof in Moderate Seismic Regionof Saudi Arabia  Article   in  ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING · October 2015 DOI: 10.1007/s13369-015-1882-8 CITATIONS 0 READS 38 3 authors:Some of the authors of this publication are also working on these related projects: Research study   View projectMuhammad AjmalKing Fahd University of Petroleum and Minerals 8   PUBLICATIONS   2   CITATIONS   SEE PROFILE Muhammad RahmanKing Fahd University of Petroleum and Miner… 63   PUBLICATIONS   213   CITATIONS   SEE PROFILE M. H. BaluchKing Fahd University of Petroleum and Minerals 139   PUBLICATIONS   994   CITATIONS   SEE PROFILE All content following this page was uploaded by Muhammad Ajmal on 16 February 2017. The user has requested enhancement of the downloaded file.  Arab J Sci Eng (2016) 41:1291–1310DOI 10.1007/s13369-015-1882-8 RESEARCH ARTICLE - CIVIL ENGINEERING Seismic Vulnerability of RC Shear Wall Building with a DomeRoof in Moderate Seismic Region of Saudi Arabia M. Ajmal 1 ·  M. K. Rahman 2 ·  M. H. Baluch 1 Received: 4 January 2015 / Accepted: 6 October 2015 / Published online: 26 October 2015© King Fahd University of Petroleum & Minerals 2015 Abstract  Recent seismic events in low-to-moderate seis-micity regions of Saudi Arabia have led to concerns on thevulnerability of RC buildings constructed in Saudi Arabiaup to mid-1990’s. These buildings were designed for gravityloads only, and potential for damage during seismic event ishigh. Buildings with dome at the roof level are an architec-tural feature in many buildings. Monolithic dome at the roof of the structure stiffens the upper part of structure requiringspecial consideration in seismic design. This paper presentsthe assessment of seismic vulnerability, using nonlinear sta-tic pushover analysis, of an eight-story building with shearwalls and a large dome at the roof level, under a moder-ate intensity earthquake. The building is located in westernregionofSaudiArabia,whichisRegion3asperSaudiBuild-ing Code. Pushover analysis iscarried out using the softwareSAP2000 incorporating inelastic material behavior for con-crete and steel, for a typical 2D frame in the building witha shear wall. The shear wall is modeled using the shell ele-ment and mid-pier approaches. A 3D pushover analysis of the building is also carried out with mid-pier model for shearwalls.Thepresenceofheavymassattheroofresultsinyield-ing of hinges in the roof-level columns supporting the dome.The beams connected to the shear wall and the shear walls of the building are deficient under seismic load. Strengtheningofbeams,columnsattherooflevelunderthedomeandshearwalls is warranted to meet the seismic demand. B M. K. 1 Civil and Environmental Engineering Department, King FahdUniversity of Petroleum and Minerals, Dhahran, Saudi Arabia 2 Center for Engineering Research, Research Institute, KingFahd University of Petroleum and Minerals, Dhahran,Saudi Arabia Keywords  Pushover analysis · Hinge formation · Shearwall · Shell element approach · Mid-pier approach · Baseshear · Interstory · Drift · Finite element 1 Introduction Seismiceventsinthepasttwodecadeshaveresultedinlarge-scalelossofhumanlivesanddamagetothestructures.Recentearthquakes including 1995 Kobe in Japan, 1999 Kocaeli inTurkey, 2005 Kashmir in Pakistan and 2010 in Chile andHaiti have highlighted the susceptibility of concrete struc-tures to extensive damage, under earthquake loading. The1994 Northridge earthquake in the USA also brings forth themassive economical losses due to damage to infrastructureand buildings designed to resist major seismic events.Saudi Arabia was generally considered aseismic for sev-eral decades. Majority of structures built up to mid 1990’swere not designed for seismic loads. Recent seismic eventsin Saudi Arabia (Tabuk 2004, Makkah 2005, Haradh 2006,Yanbu2009,Madinah2009,Jizan2014)haveledtoconcernson the safety of reinforced concrete buildings, which havenot been designed for seismic loading. The Saudi BuildingCode [1] has categorized the Kingdom into seven regionsin which the western region has been placed in Region3 with moderate seismicity. Several public and commer-cial reinforced concrete buildings constructed in moderateseismic region of Saudi Arabia are vulnerable to damageand failure during a seismic event. Buildings designed onlyfor gravity loads have limited lateral load resistance andare susceptible to column sidesway or soft story mech-anism under earthquake load. For buildings, which aredesigned for gravity and wind loads, the lack of ductiledetailing at the beam–column joint and nonadherence to  1 3  1292 Arab J Sci Eng (2016) 41:1291–1310 strong column weak beam concept makes them seismicallydeficient.Performance-based seismic design code has been imple-mented in the recent years for design of concrete structuresin many countries e.g., in USA [2–6], in Japan [7], in Europe[8]andinTurkey[9].Theperformance-basedseismic design emphasizes that public buildings such as hospitals,schools, fire stations and municipalities should remain func-tional after seismic events. Seismic capacity and seismicdemands for different performance levels of the structureneed to be computed to ensure the achievement of desiredperformance level. Two methods available to the structuralengineer to calculate seismic demand of a structure arethe dynamic time history analyses and the nonlinear staticpushover analyses.Pushover analysis of buildings is one of the performance-based seismic design approach, which can estimate forcesacting on brittle elements, identify failure mechanism of thestructure, provide interstory drifts, trace the formation of hinge and sequence of yielding of members and the capac-ityofstructureunderseismicdemand.Pushoveranalysishasbeen widely used in the recent years. It is simplified andapproximate method to evaluate the seismic performanceof structural system and to estimate the inelastic structuralresponse when subjected to lateral displacement.A large number of studies on pushover analysis of hypothetical structures have been reported in literature.Few studies addressing seismic assessment of an actualstructure using the pushover analysis have been reported.Rana et al. [10] conducted a pushover analysis of nine-teen stories, slender concrete tower building located in SanFrancisco with a gross area of 430,000 square feet. Analy-sis showed formation of hinges in walls and at spandrellocations, which was considered undesirable for the perfor-mance objective. By performing trial runs with arbitrarilyincreased shear strength of the shear hinges at these loca-tions,shear-strengtheningrequirementwasquantified.Shearstrengthening of the building enhanced the capacity of thestructure to the desired performance level. Goksu et al. [11] performed a pushover analysis of a typical RC building inTurkeywithalltypicalconstructionfaults.Theyinvestigatedthe behavior of existing and retrofitted building frame usingconcrete and CFRP jackets. The pushover analysis resultsshowed a significant enhancement in strength due to retro-fitting.3Dpushoveranalysisisanattractivealternativeforassess-ing the performance of an irregular reinforced concretebuilding. Phino et al. [12] assessed 3D irregular SPEAR testbuilding (a full-scale model tested under pseudo-dynamicconditions and subjected to bidirectional seismic loading)using four commonly available nonlinear static procedures.The comparisons with the results obtained from nonlineardynamic analysis of a verified model of the structure seemedto show that all nonlinear static pushover techniques tend tolead to reasonably satisfactory results. Fahjan et al. [13] car-ried out a nonlinear static analysis of an existing reinforcedbuilding with shear wall. They modeled shear walls for anexisting school building by mid-pier as well as shell elementmethod and found that the pushover analysis for FEMA-356model and the mid-pier model showed close results.This paper presents the nonlinear behavior of an exist-ing reinforced concrete public building in moderate seismicregion of Saudi Arabia, characterized by the presence of aheavy mass in the form of dome at the roof, when subjectedtoseismicloadingusingnonlinearstaticpushovertechnique.Usingpushoveranalysis,capacityofthestructure,targetroof displacement, interstory drift ratio, formation of hinges andsequence of yielding of members are evaluated. Pushoveranalysis is first carried out for a selected 2D frame from thebuilding with a shear wall followed by a pushover analysisof the 3D building. 2 Description of Building The structure under investigation is an existing public build-ing located in the western region of Saudi Arabia, which wasconstructed in mid-1990. The building has eight stories witha typical story height of 3.2m for first five stories, with theremaining three story heights being 4.2, 2.4 and 5m, respec-tively. The plan area of the building is 40m  ×  40m. Thebuilding consists of reinforced concrete frame elements andshear walls with ribbed and flat slab systems at different sto-ries levels except at the roof level, which has an architecturaldomewithamassofabout88,000kg.Thebuildingislocatedin the seismic Region 3 as per SBC-301 and Zone 2B as perUniformBuildingCode[14].Thesoilstrataisstiffsoilwhichplacesthestructureinsiteclass  D  asperSBC-301,andbeinga public building the importance factor (  I  ) is taken as 1.25.For Region 3, the SBC-301 stipulates the maximum spectralresponse acceleration at short periods  ( S  s )  and 1-s  ( S  1 )  are0.55 and 0.17g, respectively. 3 Modeling of the Structure for Pushover Analysis A typical plan and 3D model of the building showing thebeams and columns are shown in Fig. 1. Seismic assess- ment of the building is carried out using pushover analysis.The pushover analysis is carried out for a typical 2D framewith shear wall in the building followed by the 3D pushoveranalysis of the whole building. The 2D frame consists of twoshear walls and seven bays. Each story has different sectionsfor beams and columns. Figure 2 shows a typical frame of the building with shear walls (designated as FR1) which isselected for pushover analysis.  1 3  Arab J Sci Eng (2016) 41:1291–1310 1293 Fig. 1 a  Typical plan of building at various levels,  b  3D computer model of the building 3.1 Mechanical Properties and Loading The mechanical properties of steel reinforcement and con-crete used in the design and maintained in the constructionphaseareshowninTable1.Theaveragecompressivestrength of the concrete is 30MPa, and the yield strength of thereinforcingsteelis420MPa.Thecrosssectionandreinforce-ments in the shear walls, beams and columns are shown inTables 2, 3 and 4, respectively. Dead and live loads used for the analysis are summarized in Table 5. Dead loads consist of the weight of slabs, flooring for the selected frame, floor-ing for the roof, internal partitions and electromechanicaldevices.The seismic loads for the building are calculated usingFEMA-356 since the mass participation in the fundamen-tal mode is more than 75%. FEMA-356 design code lateralload distribution pattern is adopted which has the patternof first mode shape. The center of mass of the build-ing is calculated based on mass distribution at each node.For 3D pushover analysis, the lateral loads are appliedat the center of the mass. The accidental eccentricity isignored in the seismic loading in order to observe the lat-eral load effect on the walls. The seismic parameters forthe building as per SBC-301 and UBC-1997 are shown inTable 6. 3.2 Shear Wall Modeling For pushover analysis, the shear wall in the building is mod-eled using two approaches (1) shell element method and (2)mid-pier idealization of shear walls. In the shell elementapproach, a multilayer shell element is used which com-prises of concrete and smeared rebar layers with materialproperties as shown Fig. 3. The shell element formulation is based on the assumption that plane section remains plane.Based on this assumption, first axial strains and curvaturesare obtained for the elements, and then using constitutiverelationships, stresses are computed. The nonlinear behaviorofshearwallmodeledwithshellelementcanbeexaminedbystresses in concrete and steel layers. However, the ATC-40and FEMA-356 plastic rotation performance level cannot beassessed using this approach. The stresses in concrete andsteel can give an indication of hinge formation, but not theperformance level.In mid-pier approach, the shear wall is modeled asan equivalent mid-pier frame element and rigid beams as  1 3
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