Bir Hastane Yapısının Klasik Yöntemle Ve Sismik İzolatör Kullanılarak Tasarımının Dinamik Yönden Karşılaştırılmasının Yapılması

Abstract

Bu tez çalışmasında, perdeli ve çerçeveli bir yapı taşıyıcı sistemine sahip 8 katlı bir betonarme hastane yapısının öncelikle klasik yönteme (kapasite tasarımı ilkesi) göre tasarımı yapılmış; ardından ise klasik yönteme göre tasarımı tamamlanmış olan yapının kesit ölçüleri baz alınmak kaydıyla mevcut yapı bir kez de kurşun çekirdekli kauçuklu izolatörler kullanılarak tasarlanmıştır. Böylelikle hem sismik yalıtım uygulanarak hem de sismik yalıtım uygulanmadan tasarlanan yapının dinamik karakteristiklerinin karşılaştırılmasının yapılması ve sismik yalıtıcıların karakteristik özelliklerinin ortaya konması amaçlanmıştır. Bu tez çalışması 6 ana bölümden oluşmaktadır. Birinci bölümde simik izolasyon teorisi açıklanmış ve sismik izolatörün uygulama alanları ile ilgili bilgiler verilmiştir. İkinci bölümde değişik tipteki sismik izolasyon aletleri açıklanmıştır. Üçüncü bölümde sismik izolasyon yönteminin ön tasarım metodolojisi UBC 97 uyarınca açıklanmış ve izolatör tasarım safhaları maddeler halinde özetlenmiştir. Dördüncü bölümde yapının ankastre mesnetli olarak kapasite tasarımı ilkesi uyarınca boyutlandırılması yapılmıştır. Beşinci bölümde ankastre mesnetli olarak tasarımı tamamlanan yapının kesit ölçüleri baz alınarak önce belirlenen eksenel yük düzeyini karşılıyacak nitelikte olan iki farklı tipteki kurşun çekirdekli kauçuk izolatörün tasarımı UBC 97 Yönetmeliği’ne göre yapılmış ardından ise yapının kurşun çekirdekli kauçuk izolatörlü olarak tasarımı yapılmıştır. Altıncı bölümde ise her iki yönteme göre tasarlanan yapının zaman tanım alanında lineer olmayan analiz uygulanarak dinamik karakteristiklerinin karşılaştırılması yapılmıştır. Tez çalışmasının birinci bölümünde sismik izolasyon yönteminin teorisi açıklanmıştır. Ayrıca bu bölümde sismik izolasyon yönteminin uygulama alanları, uygulamada karşılaşılabilecek sorunlar, sismik izolatör uygulamanın olumlu ve olumsuz yanları da belirtilmiştir. İkinci bölümde değişik tipteki sismik izolasyon aletleri görsel örneklerle tanıtılmıştır. Üçüncü bölümde ise sismik izolatör tasarım metodolojisi UBC 97 uyarınca açıklanmış ve ilgili şartnameye bağlı kalınarak kurşun çekirdekli kauçuk izolatörlerin tasarımı ilk aşamadan son aşamaya değin gerekli denklemlerin açıklanmasıyla gerçekleştirilmiştir. Dördüncü bölümde yapının ankastre mesnetli olarak kapasite tasarımı ilesi uyarınca tasarımı gerçekleştirilmiştir. Ankastre mesnetli yapının tasarımı ve dinamik karakteristikleri belirlenirken ETABS programından faydalanılmıştır. Ayrıca tasarım aşamasında ETABS programının akademik çevrelerce de onaylanan ve birtakım parametreleri değiştirmek suretiyle TS 500 ve DBYBHY, 2007 ile eş değer çözüm yaptığı belirtilen ACI 318 - 99 şartnamesinden de faydalanılmıştır. Beşinci bölümde ankastre mesnetli olarak tasarımı yapılan yapının kesit ölçüleri baz alınmak kaydıyla aynı yapının bir de iki farklı tipteki kurşun çekirdekli ve kauçuklu izolatör kullanılarak tasarımı yapılmıştır. Yapıda 8 tane A Tipi ve 18 tane de B Tipi olmak üzere toplamda 26 tane kurşun çekirdekli kauçuklu izolatör kullanılmıştır. Ayrıca yüklerin üst yapıdan izolatörlere düzgün bir şekilde aktarımını sağlamak ve yatayda da izolatörlerin birbirlerine göre olan bağımsız yerdeğiştirmelerini sınırlamak bakımından izolatörlerle yapı arasında 15 cm kalınlığında rijit bir döşeme tabakası oluşturulmuştur. Altıncı bölümde ise her iki yönteme gore tasarlanan yapının zaman tanım alanında lineer olmayan analizleri yapılarak yapıların dinamik karakteristiklerinin karşılaştırılması incelenmiştir. Zaman tanım alanında analiz için 50 yılda aşılma olasılığı %10 olan tasarım depremi seviyesindeki ve 25 saniye süreli 3 benzeştirilmiş ivme kaydından faydalanılmıştır.

In this thesis , an eight storey reinforced concrete structure was designed with two different methods as implementing base isolation case and fixed base case. The structure frame system is dual system in which high ductility moment resistant frame and shear wall are combined. The main target of this research is to find the differences between base isolation concept and fixed base consept regarding dynamic characteristics of the structure. ETABS V.9.6 structural programme was used for the all structural analysis and design of the structure. Another purpose of this research is to compare the ETABS results about fixed base condition and base isolated condition. There are six main sections in the thesis. The first one is focused on the basic working theory of the base isolation systems. In addition, the subjects as the research field of the base isolation techniques, obstacles about implementing base isolation systems to the structures, disadvantages and advantages of the base isolation systems were explained in the first section. The second section is about the different types of seismic isolation tools and their working mechanism. The third section includes the isolation design methodology according to the UBC 97 codes. The design steps of the lead plug laminated rubber bearings were summarised with the step by step method in the third section. The design of the fixed base case according to capacity theory was conducted in the forth section. The structure were re-analysed and designed one more time as the lead plug laminated isolated case in the fifth section of which the structural element size’s were chosen identical with the size of the elements of the capacity method. Nonlineer time history analysis was conducted for the three different acceleration records with the size of 25 seconds. İn adition, time history analysis was conducted by the integration of the 0.005 seconds times 5000. The acceleration records were chosen by resembling them of the %10 increasing probability for the 50 years of the earthquake. İt is based on the “Specification for Structures to be Built in Disaster Areas of Turkey” codes. The isolated and non isolated case were compared in the sixth section, according to the time history analysis results regarding their dynamic characteristics as storey drift ratios, storey or base shear forces, storey accelerations etc. Conventionally, seismic design of structures is based on the concept of increasing the resistance capacity of the structures against earthquakes by employing, for example, the use of shear walls, braced frames, or moment-resistant frames. However, these traditional methods often result in high floor accelerations or large interestory drifts for buildings. Because of this, the building contents and nonstructural components may suffer significant damage during a major earthquake even if the structure itself remains basically intact. This is not tolerable for buildings whose contents are more costly and valuable than the buildings themselves, such as hospitals, police and fire stations and telecommunication centers etc. Therefore, special technique to minimize interstory drifts and floor accelerations, the base isolation technique is increasingly being adopted. Base isolation is to prevent the superstructure of the building from absorbing the earthquake energy. Therefore, the superstructure must be supported on base isolators to uncouple the ground motion, The basic objective with seismic isolation is to introduce horizontally flexible but vertically stiff components (base isolators) at the base of a building to substantially uncouple the superstructure from high-frequency earthquake shaking. The basic concept of base isolation system is lengthening the natural period of the fixed base building. Increasing the period of the structure reduces the spectral acceleration for typical earthquake shaking. Displacements in isolated structures are often large and efforts are made to add energy dissipation or damping in the isolation system to reduce displacements. The addition of damping to the isolation systems serves to reduce displacements in the seismic isolators, which can translate into smaller isolators. In order to minimize interstory drifts, in addition to reducing floor accelerations, the concept of base isolation is increasingly being adopted. Base isolation has also been referred to as passive control, as the control of structural motions is not exercised through a logically driven external agency, but rather through a specially designed interface at the structural base or within the structure, which can reduce or filter out the forces transmitted from the ground. In contrast, the techniques of active or structural control, which are still under research and development for the seismic resistance of structures, require the installation of some logically controlled external agencies, such as actuators, to counteract the structural motions. One drawback with active control techniques is the relatively high cost of maintenance for the control system and actuators, which should remain functional at all times in order to respond to a major earthquake. There also exists a third category of techniques, called hybrid control, that make use of the best of both passive control and active control devices. In this thesis, there is no discussion of either active or hybrid control. A practical seismic isolation system should meet the sufficient horizontal flexibility to increase the structural period and spectral demands, except for very soft soil sites, sufficient energy dissipation capacity to limit the displacements across the isolators to a practical level and adequate rigidity to make the isolated building no different from a fixed-base building under general service loading. Most commonly used seismic isolating systems can satisfy all the above requirements. Certainly, if the seismic isolating system can be equipped with fail-safe devices for avoiding the total collapse of the isolated structure in cases where excessive displacements occur, then the system will most likely be satisfactory. In the past two decades, the technology of seismic isolation has evolved along the lines of similar principles, resulting in the invention of one isolation device after the other. Most of the seismic isolation devices available in the market satisfy the basic requirements identified above, while having their own characteristics. Commercially available seismic isolation systems can be classified according to their dynamic characteristics and how they are formed from individual devices. There are many different techniques to isolate the structure from the effects of the earthquakes. Most systems used today incorporate either elastomeric bearings, with the elastomer being either natural rubber or neoprene, or sliding bearings, with the sliding surface being teflon and stainless steel. Systems that combine elastomeric bearings and sliding bearings have also been proposed and implemented. The examples of elastomeric-based systems are low-damping natural and synthetic rubber bearings, lead-plug bearings, high-damping natural rubber (hdnr) systems. Isolation systems based on sliding are electricité-de-france system, eerc combined system, the tass system, friction pendulum system, spring-type systems, gerb system and sleeved-pile ısolation system. Compared with the elastomeric and lead rubber bearings, most friction systems have the advantage that they are not affected either by the natural frequency of the isolated structure or the frequency content of the earthquake. The coefficient of friction is the key parameter that determines whether or not sliding will occur with the system. However, most friction systems have the drawback that they are incapable of returning the structure to its original position. It is likely that permanent offset may exist between the sliding parts of the system after a major earthquake. Lead plug laminated bearings are composed of alternating layers of rubber that provide flexibility and steel reinforcing plates that provide vertical load carrying capacity. At the top and bottom of these layers are steel laminated plates that distribute the vertical loads and transfer the shear force to the internal rubber layer. On the top and bottom of the steel laminated plate is a rubber cover that provides protection for the steel laminated plates laminated rubber bearings similar to low damping rubber bearings, but contain holes into which one or more lead plugs are inserted. The lead must fit tightly in the elastomeric bearing, which is achieved by making the lead plug slightly larger than the hole and forcing it in. Because the effective stiffness and effective damping of the lead plug laminated rubber bearings depend on the displacement, it is important to state the displacement when a damping value is specified or reported for an lead plug laminated bearing. İt is a known fact that the use of isolators is generally prevent the structural damage, limit the maximum lateral deformations and accelerations of the stories of the buildings and guarantee the protection of non structural components and equipments. Several surveys carried out in the aftermath of major earthquakes have, in fact, demonstrated that the economic losses in the structures are caused primarily by their contents and architectural parts. Therefore it is of paramount importance when designing earthquake-resistant structures, particularly those used for emergency management, to account properly for the operational limit state in addition to the life safety limit state. There are many advantages of designing any building with the base isolation technology. Especially the damage level of the upper part of the structure is limited and decreased to the minimum level. This is especially important for the structures of which must be immediately used after of a large earthquake, as hospitals. On the other hand, different from fixed base structures, the damage risk of the non structural but expensive or valuable elements are more protected because of the decreasing of the building storey accelerations. The upper part of the structure behave as a rigid body and bending deformations, crack formation and plastic deformations of the elements are limited. The reaction forces are decreased especially for the beam – column joint points of which are the most critical zones of the structure. Moreover, different from conventional design methodology the base isolated design is more clear and easy due to the complexity and the indeterminities content of the earthquake is decreased. There are some disadvantages or non beneficial conditions of using base isolaion technology. If the structure is a tall building or the structure located to the soft soil base isolation should not be implemented .The natural period of the tall building is already high and there may be resonance risk for the the structure of which located to the sof soil. In addition there may be overturning risk for the tall building. In this thesis two types of 26 lead plug laminated rubber bearings were used named A and B. They were installed on the base level of the structure with a thick slab layer of which size is 15 centimeters. The slab layer is due to it creates a rigid diaphram in the horizontal directions of the structure by providing the same horizontal displacements of the isolators and it contributes to homogeneous load transfer from the structure to the isolators. The isolated and fixed based models were compared according to nonlinear time history analysis results. The story accelerations are reduced significantly in the base-isolated building compared to the fixed base building. The story drifts of the building is also reduced for the base isolated structure compared to the fixed base structure and the behoviour of the structure as a rigid body. The more the period is lengthened, the lesser the story accelerations and story drifts of the superstructure above the base isolators. The displacements are increased with period in the base isolated structure.