Mevcut betonarme bir konut yapısının deprem performansının değerlendirilmesi ve çelik çaprazlarla güçlendirilmesi
Seismic performance assessment of an existing reinforced concrete structure and strengthening with steel braces
Yazar: ALİ ERDEM KULAK
Danışman: DOÇ. DR. ELİŞAN FİLİZ PİROĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Mevcut yapıları depreme karşı güvenli hale getirmek için çeşitli güçlendirme metodları kullanılmaktadır. Bu metodlar kullanılmadan önce mevcut yapının performans değerlendirilmesi doğrusal veya doğrusal olmayan hesap yöntemleri ile yapılmaktadır. Performans değerlendirilmesi yapıldıktan sonra yapının kullanımamacını ve mimari özelliklerini en az etkileyecek güçlendirme yöntemi seçilmektedir. Güçlendirme safhasında da kullanılması gereken yapıları, fonksiyonlarını engellemeden güçlendirmek için dünyada giderek yaygınlaşan bir anlayışla çelik çaprazlar kullanılmaktadır.Altı bölümden oluşan yüksek lisans tezinin birinci bölümü, konunun açıklanmasına ve konu ile ilgili çalışmaların gözden geçirilmesine ayrılmış, çalışmanın amacı ve kapsamı hakkında bilgi verilmiştir.İkinci bölümde, yapı sistemlerinin statik ve dinamik etkiler altındaki doğrusal olmayan davranışları incelenmekte ve doğrusal olmayan yapı sistemlerinin hesap yöntemleri gözden geçirilmektedir. Bu bölümde, malzeme bakımından doğrusal olmayan betonarme kesitlerin iç kuvvet-şekildeğiştirme bağıntıları verilmiş, doğrusal olmayan şekildeğiştirmelerin belirli kesitlerde toplandığı varsayımına dayanan plastik mafsal hipotezi ve bu hipotezi esas alan hesap yöntemi açıklanmıştır. İlerleyen kısımlarda, doğrusal elastik olmayan sistemlerin deprem davranışı üzerinde durulmuş, binaların deprem davranışında önemli rolü olan süneklik ve sünekliğe katkı sağlayan sargı etkisi gözden geçirilmiştir.Üçüncü bölümde, yapıların performansa dayalı tasarımı ve değerlendirilmesi hakkında bilgi verilmektedir. Bu bölümde, 2007 Türk Deprem Yönetmeliği?nde tanımlanan kesit hasar düzeyleri, performans seviyeleri ve çoklu performans hedefleri özetlenmiştir. Ek olarak, doğrusal olmayan analiz yöntemlerinden olan ve bu çalışmada kullanılan artımsal eşdeğer deprem yükü yöntemi açıklanmıştır.Dördüncü bölümde, sayısal incelemeler ve hesaplarda izlenen yollar yer almaktadır. Bu bölümde, dikkate alınan binanın deprem performansı doğrusal olmayan yöntemler kullanılarak belirlenmiştir. Binanın deprem performansı değerlendirmesinde, 2007 Deprem Yönetmeliği?nde tanımlanan doğrusal elastik olmayan değerlendirme yöntemlerinden artımsal eşdeğer deprem yükü yöntemi ile kesit hasar bölgeleri, taban kesme kuvvetleri ve tepe noktası yatay yerdeğiştirmeleri belirlenmiştir.Beşinci bölümde, güçlendirme hesabında kullanılacak kabuller, kullanılan çelik çapraz türleri açıklanmıştır. Performansa dayalı tasarımda Fema yaklaşımına değinilmiştir. İlerleyen bölümlerde güçlendirmede kullanılan merkezi çelik çaprazlar ve dış merkez çelik çaprazlardan sonra betonarme yapının performans analizi tekrar edilmiştir. xxivAltıncı bölüm, bu çalışmada varılan sonuçları kapsamaktadır. Çalışmanın başlıca özellikleri, sayısal sonuçlarının değerlendirilmesi ve konunun olası genişleme alanları bu bölümde sunulmuştur.

Abstract:
Various strengthening methods have are being applied for existing structures to makethem safe against earthquake. The seismic performance of structures may be assessedby means of either linear or nonlinear methods before applying strengtheningmethods. Following assessment of eartquake performance of the structure, strengthening methods that have the least impact on the purpose of its usage and architectural properties. Steel bracing is worldwide becoming an increasingly common approach in strengthening structures without hindering their functions. This kind of strengthening is very usefull for schools, factories, hospitals and government buildings.The assessment of the reinforced concrete structure is done according to Turkish Earthquake code 2007. In the first section, general information is given about topic,aim and the scope of the study. The nonlinear behavior of the structure is explained in the next chapter. Second chapter gives the technical background of nonlinear analysis. The third chapter deals with performance based design and assessment of structure. Performance levels and pushover analysis is explained in this chapter. Structure modal and information of building is studied in the fourth chapter. The assessment of reinforced concrete structure is done at the end of this section. Strengthening design is explained at chapter five. Two different steel brace types are explained in this section for strengthening design. Finally in the sixth chapter, results are given. Detailed summaries of each chapter are explained below.In the first section of this Master of Science thesis comprising six sections is assigned to description of the subject and review of the studies related to subject and provide information on the objective and scope of the study. The meaning and thehistory of performance based design is mentioned in this section. Milestones of this Master of Science thesis is also given at the end of section one.In chapter two, the nonlinear static and dynamic behaviour of structural systems are reviewed and nonlinear analysis methods are investigated. In this chapter the internal force-deformation relationships of reinforced concrete sections with material nonlinearity are given and the basic principles of plastic hinge theory and the load incremens method based on this theory are explained.The reasons of being nonlinear of structural systems are discussed. In section 2.3, design of nonlinear (in terms of material) reinforced concrete systems are studied. The nonlinear behavior of systems under external loads are mentioned and tabulated. xxviIn the following sections, dynamic behaviour of nonlinear systems, dynamic equilibrium equations and controlling parameters are discussed, and ductility concept and confinement effect, which have significant role in seismic behaviour of structural systems are presented. In the last section of chapter 2, behavior of buildings under earthquake loads are mentioned in terms of, damping, ductility. Mander concrete modal is explained for having a reinforced concrete structure.The third chapter gives a general information on performance based design and assessment of structures. In section 3.1, gathering information of an existing building is explained according to Turkish Earthquake Code 2007. In chapter 3.2 the sectionaldamage limits, in section 3.3 building performance levels and multiple performance objectives are stated and explained according to 2007 Turkish Earthquake Code. Section 3.4 deals with the earthquakes, which will be considered during the assessment of structure. After this section, performance aim is discussed for different structure types. In the last section, one of the nonlinear methods, incremental equivalent earthquake load method is explained. The milestones of push-over analysis are mentioned in section 3.6.4.In the fourth chapter, seismic performance of the structure is evaluated according to the non-linear elastic methods. The structural system is explained in section 4.1.Considered structural system has seven stories with height of 3.5 m. In X direction, it has 4 bays with a span length of 7.00m and it has 3 bays in Y direction with a span length of 7.00m and 4.00m. The concrete quality of considered structure is BS 17 and STIII-a reinforcement bars used. The bearing system consists of moment frames in both directions. Thera are four very rigid shear-walls in Y direction. X direction is more slender than Y direction because of not having any shear-walls at X direction. Before analysis, it is expected that X direction would be weaker than Y direction.The building is considered to place in first degree earthquake zone. According to Turkish Eartquake Code 2007, soil class is Z3. Structure is used as residantal building so performance objective is life safety under D2 earthquake according to Turkish Earthquake Code 2007. The building mode in X direction is 2.067s and 0.75s in Y direction. The difference between modes are because of having four very rigid shear walls at Y direction.Firstly, building analyzed under gravity loads. The result of this analysis is considered initial condition of pushover alaysis. The roof displacement demand is 51 cm for X direction and 0.17 cm for Y direction. The building is pushed until top displacement reached these values. The base shear forces, lateral displacements of its peak point and the seismic performances of the building is determined in conformance with incremental equivalent earthquake load method defined in the 2007 Turkish Seismic Code.As a result of pushover analysis, building could not achieve the life-safety performance at X direction because of having very big top displacement demand. In the fifth chapter, assumptions to be employed in strengthening calculations and type of steel bracings to be used are explained. Performance based design approach of FEMA is mentioned. Performance objectives are discussed according to FEMA 356.xxviiIt is aimed to reduce the displacement demand of system during strengthening phase. Two type of steel bracing used in strengthening design. First one is concentric steel braces, second one is eccentric steel braces. These braces are placed in X direction in order to reduce the X direction top displacement demand of structure. In the following sections, performance analysis of the reinforced concrete structure is repeated after strengthening by concentric and eccentric steel braces.System solved under gravity loads and this analysis considered initial condition of push-over analysis. Plastic hinge properties which described in FEMA 356 for steels are assigned to steel braces.By using the concentric braces top displacement demand of structure is reduced to 0.17 cm in X direction. Structure achieved to reach life-safety performance under D2 earthquake. Steel members are observed to reach collapse prevention performance. After using concentric braces, system analyzed once again for eccentric steel braces. The top displacement demand is reduced from 0.51 cm to 0.23 cm in X direction. Structure achieved to reach life-safety performance under D2 earthquake. Steel members are observed to reach collapse prevention performance. The sixth chapter contains the results reached in this study. The basic features of the study, the assessment of the numerical results and the posssible extensions of the study are presented in this chapter.It is shown that a structure,one direction is weaker than the other direction, can be strengthened with steel braces. Both type of steel braces are reduced the top displacement demand of structure. After a strong earthquake steel braces can be switched with new ones and can show same performance again. It is strongly recommended that solve the structural irregularities of structure before strengthening phase.Concentric braces are more effective than the eccentric braces for strengthening in one direction. The joint points of where steel braces anchorage to concrete is very curicial and need to be designed carefully. It is very important to mantle these pointsif concrete quality is poor.