Mevcut 25 katlı betonarme bir yapının deprem performansının incelenmesi
Seismic performance assesment of an existing reinforced concrete tall building
Yazar: AHMET CAN ÖZGELDİ
Danışman: PROF. DR. HASAN BODUROĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Deprem Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Deprem Mühendisliği = Earthquake Engineering ; İnşaat Mühendisliği = Civil Engineering
Dizin: Deprem kayıtları = Earthquake records ; Deprem yükü = Earthquake load ; Depreme dayanıklı binalar = Earthquake resistant buildings ; Performans esaslı tasarım = Performance based design ; Yapı davranışı = Structure behavior ; Yapı dinamiği = Structural dynamics ; Yüksek yapılar = High structures

Özet:
İstanbul'da yüksek yapı inşaatında gözle görülür bir artış vardır. Dizayn ofisleri,yüksek yapı tasarımında, yaygın olarak kuvvet esaslı tasarım yöntemini DepremBölgelerinde Yapılacak Binalar Hakkında Yönetmelik'e (DBYBHY) (2007) göreuygulamaktadır. Yüksek yapılar için geleneksel tasarım yöntemleri ekonomikolmayan sonuçlar vermektedir. Yüksek yapıların tasarımı, nonlineer analizin pratikteuygulanmasının kolaylaşması ile değişmiştir. Yüksek yapıların performans bazlıtasarımına yardımcı olması için İstanbul Yüksek Binalar Deprem Yönetmeliği(İYBDY) (2008) DBYBHY'e alternatif olarak ek yol gösterici bir rehber olarakyayınlanmıştır. Fakat az sayıda yapı İYBDY'deki performans esaslarına göretasarlanmaktadır.DBYBHY ve İYBDY'de yapı ve deprem mühendisliğinin modern gereklerine sahipolmalarına rağmen, bazı eksikleri vardır. Bu yönetmeliklerdeki tasarımprosedürlerinin uygulanması ekonomik olmayan çözümlere neden olabilir.Performans esaslı tasarım, mühendislere binanın depremde nasıl davranışgöstereceğini tahmin etmesi için olanak sağlar.Yüksek yapıların performansının incelenmesinin genel amaçlı tasarım yönetmelikleritarafından yapılması doğru değildir. Yüksek yapıların, davranış farklılıkları sebebiyleözel olarak incelenmesi gerekmektedir.Pasifik Deprem Mühendisliği Araştırma Merkezi (PEER), Guidelines forPerformance-Based Seismic Design of Tall Buildings (2010) rehberini yüksekyapıların performans esaslı tasarımı konusunda eksiklik için yayınlamıştır. Burehberin amacı yüksek yapıların tasarımında daha ekomomik sonuçlar, dahagüvenilir sismik performans analizi, yenilikçi taşıyıcı sistem ve malzeme kullanımısağlamaktır.Sunulan bu tezde, İstanbul'da bulunan 25 katlı betonarme bir binanın performansı,PEER tarafından yayınlanan Guidelines for Performance-Based Seismic Design ofTall Buildings (2010) rehberinde tanımlanan ?Maximum Considered Earthquake?(MCE) deprem etkisi altında performansı göre incelenmiştir.Konuya yönelik olarak depreme dayanıklı tasarım felsefesi ikinci bölümdeanlatılmıştır.Üçüncü bölümde yüksek yapıların tasarımı anlatılmıştır. Yüksek yapıların tanımı,yüksek yapıların tasarımında kullanılabilecek analiz yöntemleri, deprem düzeyleribilgileri verilmiştir. Özellikle doğrusal olmayan analizlerde yapılacak malzemedavranışı ile ilgili kabuller ve eleman davranışınıyla ilgili kabuller de bu bölümdeaçıklanmıştır.Dördüncü bölümde ise bu tez çalışması için seçilen örnek betonarme yapının zamantanım alanında doğrusal olmayana analizi için yapılan SAP2000 ve Perform-3Dmodelleri, bu modellerde yapılan kabuller verilmiştir. Aynı bölümde MCE depremdüzeyi için seçilen hedef spektrum, binanın konumuna ve etkisi altında olduğu fayetkisine göre seçilen deprem kayıtları ve bu kayıtların ölçeklendirilmesi de bulunmaktadır. Son olarak mevcut bina için yapılan zaman tanım alanında doğrusalolmayan analizlerin sonucu, yapı elemanlarının hasar durumları verilmiştir.Çalışmanın beşinci bölümünde ise elde edilen bulgular tartışılmış, sonuç ve önerilerverilmiştir.

Abstract:
There's a significant raise in construction of high-rise buildings in Istanbul. Leventarea is the new skyline of Istanbul where tall office buildings of major companies arelocated.Design offices are generally applying force-based design approach for high-risebuildings with Turkish Earthquake Resistant Design Code (TERDC). Traditionaldesign approaches may not give economic results in design. They need to designedand investigated carefully for lateral loads with the modern approaches since theyoccupy many people inside and a possible collapse from the expected earthquake inIstanbul can be a disaster.Design of tall buildings have changed since it has become easier to use nonlinearanalysis in practical engineering. For the need of performance-based design of tallbuildings, the draft named Istanbul High Rise Buildings Earthquake Code (IHRBEC)was published as an alternative guide. Yet still there are few buildings designed withperformace-based design.Even though both TERDC and IHRBEC have the modern needs of structural andearthquake engineering, they are still lacking in some points. They don?t havespecific information about the nonlinear behaviour of components of the tallbuildings or damping in tall buildings. Design application with these building codesmay result in uneconomic construction cost, inadequate section dimensions andreinforcements.Inspection of high-rise building performance with general building codes is not theproper attitude. Tall buildings must be inspected specifically because of their unusualbehavior than common buildings.PEER have published Guidelines for Performance-Based Seismic Design of TallBuildings (2010) for the need of a specific code for tall buildings. Scopes of thisguideline are reduced construction cost and probably most importantly more reliableperformance analysis and use of innovative structural systems and materials.In this work, a 25 story reinforced concrete building in Istanbul is analyzed underMaximum Considered Earthquake (MCE) force as suggested in Guidelines forPerformance-Based Seismic Design of Tall Buildings (2010).As related to the subject of this work, fundamentals of earthquake resistant designare explained in chapter two.In chapter three, design of tall buildings is explained in details. Definition of tallbuildings from different building and design codes can be seen in this chapter.Analysis methods to be used in the design of tall buildings are described in details forboth linear and nonlinear analysis types. Guidelines that have been used in this are Guidelines for Performance Based Design of Tall Buildings (PEER, 2010) andModeling and acceptance criteria for sesismic design and analysis of tall buildings(PEER, 2010).Nonlinear behaviour of reinforced concrete, assumptions and analytical modelswhich are going to be used for nonlinear analysis are parts of the third chapter.Modelling of structural elements for nonlinear analysis are also described. Besidesmodelling informations, there are also information about selection of target spectrumfor the earthquake records to be used in nonlinear time history analysis.Chapter four consists modelling information about the reinforced concrete chosen forthis work. 25 story, 90m high building and its place on istanbul is shown in figure.Size of sections of this building, like beams,columns, shear walls, are given detaillyin tables. Building materials are concrete which has 35Mpa characteristic strengthand reinforcement which has 420Mpa yield strength.Structure is modeled in both SAP2000 and Perform-3D softwares. Building haswaffle slabs in each floor. Waffle slab is modeled with shell sections which haveequivalent stiffnes as waffle slabs used in this structure.For nonlinear analysis plastic hinges of frame elements (beam and column) areassumed at the start and end point of frames. Plastic hinges are where plasticdeformation due to lateral loads occur. For defining plastic hinge, one has to predictthe behaviour of section. Confinement are considered for straing and stress ofconcrete in beams and columns. Moment-rotation or moment-curvature relations ofsections are obtained by using Xtract software. After obtaining this relationship,plastic deformation capacity are defined in hinges. Plastic hinges are not assigned toshear walls, since it is to be investigated by Perform-3D.In Perform-3D model, shear walls are defined by using fiber sections. Reinforcementfiber sections are defined by using longitudinal reinforcement ratios. Shear walls aremodeled by using reinforcement fiber sections and concrete fiber sections parallel.So they work together. Strain gages are defined for obtaining compression andtension strain at the edge of the shear walls. Rotation gage is also defined forobserving rotation of shear walls.Deformations for the acceptance criteria in ASCE41 (2006) have been used for thestructural components.Four strong motion records are for nonlinear time history analysis from PEER strongmotion database in relation with the distance of building to fault, faulting type andmagnitude. Records are then scaled with the software EZ-FRISK to match targetspectrum which is chosen from IHRBEC since studied case is located in Istanbul.In the last chapter, results of the analysis are discussed. After the analysis it isobserved that some columns at corner and the edge of the structure are beyond thecollapse prevention performance level. Especially in Y direction due to poorstructural system, tension forces such like 2500 kN have occured in columns and thishad caused the column failure. Damaged beam components are all in Instant Occupydamage level. More information about damaged percentage of beams and columnsare given with graphs in the fifth chapter.Tension strains observed at the edge of first floor shear walls show that yieldingpoint has been passed and plastic hinging has occured. Rotations of shear walls are inthe limits which have been decided by ASCE41 (2006).Shear walls at the first story have been checked for shear failure. Shear nominalstrength of walls have been calculated according to given formula in ACI318-11(ACI318, 2011, S. 21.11.9). It is observed both in SAP2000 and Perform3D analysisresults that some shear walls are affected by higher shear forces than allowed inACI318-11. This leads to failure of walls under MCE excitation.Story drifts of each analysis have been found and mean of these dritfs have beencalculated. Story drifts in X direction does not exceed the required limits, but in Ydirection some stories exceed the limits suggested by GPBSDTB.As a result it is decided that the structure has performed as expected performancelevel under MCE effect.During the analysis some problems have been encountered. Equivalent frame modelof shear walls which have hinges in SAP2000 has created convergence problem fornonlineer time history analysis. From some point on analysis has started not toconverge and as a result it caused unfinished analysis. Due to this problem it is wiserto use Perform-3D for such cases. Another problem is tension forces in columns. Useof waffle slab has created a poor structural system and poor beam-column joints.90% of the earhquake force of this structure is affecting shear walls which isunusually high. There may be a regulation or suggestion in IHRBEC for thestructural system.Yet even though building has poor structural system, building is still in expectedperformance level because of high percentage reinforcements and large sections. It ishighly recommended that design of tall buildings should be carried out with a specialcode with modern approaches for this type of buildings in order to have economicsand reliable results.