Behaviour Of Reinforced Concrete Buildings With Irregular Slabs Under Earthquake Effects

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015Thesis (M.Sc.) -- İstanbul Technical University, Instıtute of Science and Technology, 2015Yüksek Lisans tezi olarak hazırlanan bu çalışmada Deprem Bölgelerinde Yapılacak Binalar Hakkında Yönetmelik 2007' de belirtilen A3- Planda Çıkıntı Düzensizliği' ne sahip binaların deprem davranışları incelenmiştir. Deprem yükleri altında binaların analizinde genel olarak döşeme sisteminin sonsuz rijit olduğu düşünülerek, döşemelerin rijit diyafram davranışı gösterdiği kabul edilir. Bu yaklaşımın planda düzensiz binalar için geçerliliğini kontrol etmek amacıyla, aynı kat planına sahip, taşıyıcı sistemleri farklı olan iki bina sistemi analiz edilmiştir. Bu tez çalışmasında incelenen binalar, planda çıkıntı düzensizliği bulunan, aynı kat planına sahip, çerçeve taşıyıcı sistemli 6 katlı ve perde-çerçeve taşıyıcı sistemli 12 katlı olarak seçilmiştir. Bu binaların üç boyutlu modellemesi yapılarak, döşemelerin esnek ve rijit diyafram olarak çalıştığı kabulleri ile deprem ve diğer yükler altında çözümlemeler yapılarak sonuçlar karşılaştırılmıştır. Yapılan çözümlemeler sonucunda yapıların periyotları, taban kesme kuvvetleri, düşey taşıyıcı elemanlarda oluşan moment ve kesme kuvveti değerleri karşılaştırılmıştır. Her iki yaklaşım için döşeme kalınlığı da parametre olarak alınarak, döşeme kalınlığının rijit diyafram ve esnek diyafram yaklaşımlarına etkisi incelenmiştir. Ayrıca aynı sistemler yine döşeme kalınlığı parametre olarak alınarak, farklı döşeme kalınlıkları ile sadece deprem yükleri altında analiz edilerek, döşeme gerilmeleri, kolon - döşeme ve perde - döşeme birleşim noktalarında oluşan gerilme değerleri incelenmiştir. Tez çalışması aşağıdaki bölümlerden oluşmaktadır: • Birinci bölümde, çalışma konusunun tanıtılması, çalışmanın amacı ve kapsamı, daha önce yapılan çalışmalar hakkında bilgiler yer almaktadır. • Çalışmanın ikinci bölümünde, deprem yönetmeliğinde tanımlanan düzensizlik durumları hakkında genel bilgi verilmiştir. • Üçüncü bölümde, bina sistemlerinin deprem yükünün hesabı için yönetmelikte verilen deprem yükü hesap yöntemleri incelenmiş ve bu yöntemler hakkında bilgi verilmiştir. • Dördüncü bölümde, kat döşemelerinin rijit diyafram yaklaşımı ve esnek diyafram yaklaşımı ile modellenmesi hakkında genel bilgi verilmiştir. • Sayısal örneklerin olduğu beşinci bölümde ise aynı kat planına sahip iki farklı tip bina sistemi ele alınarak bu sistemlerin iki ayrı modelleme ile düşey ve deprem yükleri altında analizi yapılmış, bina sistemlerinin yönetmelikte belirtilen düzensizlik kontrolleri yapılmış ve düşey elemanlarda oluşan kuvvetler hesaplanmıştır. Elde edilen sonuçlarda bina periyotları, taban kesme kuvvetleri, taşıyıcı elemanlarda oluşan iç kuvvetler karşılaştırılmıştır. Aynı bina sistemleri döşeme kalınlığı arttırılarak yeniden modellenmiş, yapılan çözümleme sonucunda elde edilen periyot, taban kesme kuvvetleri, taşıyıcı elemanlarda oluşan iç kuvvetler karşılaştırılmış ve döşeme kalınlığının bu sonuçlara etkisi belirlenmiştir. • Altıncı bölümde söz konusu bina sistemlerinde, döşeme gerilmelerinin farklı döşeme kalınlıklarına bağlı olarak değişimi incelenmiştir. Döşeme kalınlığı parametre olarak alınarak, 12, 14 ve 16 cm döşeme kalınlıkları ile modellenen binalar sadece deprem yükü altında analiz edilerek, kat döşemelerinde ve kolon-döşeme, perde - döşeme birleşim bölgelerinde oluşan maksimum asal gerilme değerleri karşılaştırılmış ve döşeme kalınlığının gerilme değerlerine etkisi irdelenmiştir. • Yedinci bölümde ise sayısal örneklerde elde edilen sonuçlar verilmiş ve bu sonuçlar yorumlanmıştır.Earthquake motion which effects structures during their service life may be very destructive. Unfortunately, 92% of Turkey is under the risk of destructive earthquakes. For design of structural systems, the resistance of the buildings against seismic force is one of the main principles. The latest Turkish earthquake code - Specification for Buildings to be Built in Seismic Zones (DBYBHY 20007) was brought into force in 2007 in order to design earthquake resistant structures. Regular structural systems are encouraged in the code while it is advised to avoid the design of irregular structures as possible as we can. The main purpose of the present study is to investigate the behaivour of reinforced concrete buildings with irregular slabs under earthquake effects. In this study, A3 type irregularity; projecting parts in plan, as defined in DBYBHY 2007 is investigated. In the structural analysis of buildings, floor slabs are usually assumed to be rigid in their planes. This assumption simplifies the solution whether approximate techniques or more elaborate computer analyses are used. For most regular structures, this approach is generally satisfied. It is necessary, therefore, to verify this approach for irregular structures. In this study, the differences between the rigid floor and flexible floor analyses of irregular buildings are investigated. The equivalent lateral force method is used to analyze the buildings. The structures studied are reinforced concrete building frames with 6 and 12 stories. 6 storey-building is considered without shear walls while 12 storey-building is considered with shear walls. For each building periods, base shear forces, bending moments and shear force values of vertical structural elements are calculated and compared. Also, in order to determine the effect of the slab thickness between rigid and flexible floor assumptions, same buildings are analyzed with different slab thicknesses. Also, the variation of slab stresses based on different slab thickness is investigated. The study consists of the following divisions: • In the first chapter, the subject of the study is explained. The purpose and scope of the study and information about past studies are given briefly. • In the second chapter of the study, irregularities defined in DBYBHY 2007 are examined. According to DBYBHY 2007, design and construction of irregular buildings should be avoided because of their unfavourable seismic behaviour. There are two main irregularities, first one is irregularities in plan while the other one is irregularities in elevation. Irregularities in plan consist following three types; i. A1 - Torsional Irregularity, ii. A2 - Floor Discontinuities iii. A3 - Projections in Plan. Irregularities in elevation consists following three types; i. B1 - Interstorey Strength Irregularity (Weak Storey) , ii. B2 - Interstorey Stiffness Irregularity (Soft Storey), iii. B3 - Discontinuity of Vertical Structural Elements. A3 - Projections in plan is the main subject of this study and it is defined in DBYBHY 2007 as, the cases where projections beyond the re-entrant corners in both of the two principal directions in plan exceed the total plan dimensions of the building in the respective directions by more than 20%. According to the DBYBHY 2007, buildings with irregularity types A2 and A3, in the first and second seismic zones, it shall be verified by the calculation that the floor systems are capable of transferring the seismic loads safely between vertical structural elements. • In the third chapter, the methods to be used for the seismic analysis of buildings and building-like structures are given and explained. According to DBYBHY 2007, there are three main methods for calculating earthquake loads. Those are Equivalent Seismic Load Method, Mode-Combination Method and Analysis Methods in the Time Domain. In this study equivalent seismic load method is used. According to DBYBHY 2007, The Equivalent Seismic Load Method may be used for, I. In the first and second seismic zones, buildings with torsional irregularity coefficient satisfying the condition ηbi ≤ 2.0 at every storey, building height less than 25 m. II. In the first and second seismic zones, buildings with torsional irregularity coefficient satisfying the condition ηbi ≤ 2.0 at every storey and at the same time without the type B2 irregularity, building height less than 40 m. III. In the third and fourth seismic zones, all buildings, building height less than 40 m. Investigated structures satistified this conditions. • In the fourth chapter of the study, general information about the rigid and flexible floor assumptions are given. For building analyses under the rigid floor assumption, each rigid floor contains a master node with three degrees of freedom at the mass center of the floor to control the two in- plane translations and one out-of-plane rotation of all the slaved nodes in this rigid floor. For building analyses under the flexible floor assumption, each node contains six degrees of freedom - three translations and three rotations. • In the fifth chapter of the study, the numerical examples are given. The structures considered in the present study are frame buildings with 6 and 12 stories. 12 storey-building is designed with shear walls while 6 storey- building is degisned without shear walls. Both of them have same story plans, story height is 3.20 m for each storey. All beams are selected as 30/60 cm. Because of the symmetric storey plan, 12 columns are investigated for 6 storey building and 6 columns and 4 shear walls are investigated for 12 storey building, respectively. Buildings are selected in the first zone. Building importance factor is selected as I=1.5 because the buildings designed as hospital. Each building slab is selected as two-way slab and the slab thickness is takes as 12 cm. Those buildings are analyzed under rigid floor and flexible floor assumptions. Thus, two analyses are used for each building. Base shear forces and story shear forces are calculated by using equivalent seismic load method. Irregularities specified in DBYBHY 2007 are checked and irregularity coefficients have satisfied the conditions. As a conclusion of analysis, the variation of shear forces and bending moments of vertical structural elements are given in tables. In order to determine the effect of the slab thickness between rigid and flexible floor assumptions the same buildings are analyzed with different slab thicknesses. First part of the slab thickness of 12 cm is examined. After having the results of the first part, the same systems are analyzed with slab thickness of 16 cm. • In the sixth chapter of the study, the variation of slab stresses based on different slab thickness is investigated. The structures used in chapter five, are analyzed under only earthquake load. 6 and 12 storey-buildings with slab thicknesses of 12, 14 and 16 cm are analyzed under earthquake load. Those buildings are analyzed under rigid floor and flexible floor assumptions. Thus, two analyses are used for each building. Maximum principle stress values of each storey are shown in figures and tables. • In the last chapter of the study, the results obtained from analyses are given and commented. As the conclusion of this study, it is found that, • The internal forces in vertical structural elements in framed system does not differ much while the difference is higher at the framed - shear walled systems. For the buildings without shear walls the rigid floor model is as accurate as the flexible floor model. For the buildings with shear walls the rigid floor and the flexible floor model analyses can differ much more compare to the framed buildings. It was shown that, for frame and frame with shear walls sytems, the increase in the floor stiffness leads to a decrease in difference between the resulst of rigid floor and flexible floor analyses. • The stress concentrations at the slabs are mainly located in the regions close to the walls. In slabs, the maximum principle stresses are formed at endpoint of columns in framed systems and formed over shear walls in framed - shear walled systems. • Maximum principle stresses of each storey are smaller for framed systems, however, those calculated for framed - shear walled systems are higher. It has shown that, for framed and framed - shear walled sytems, the increase in the floor stiffness leads to increase in the maximum principle stresses at the same time. Maximum principle stresses of each storey are higher for the flexible floor assumption compare to the rigid floor assumption.Yüksek LisansM.Sc