Mevcut betonarme bir binanın güçlendirme öncesi ve sonrası deprem güvenliğinin belirlenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75208
- Danışmanlar: PROF. DR. ERKAN ÖZER
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: İşletme Ana Bilim Dalı
- Bilim Dalı: İş İdaresi Bilim Dalı
- Sayfa Sayısı: 101
Özet
ÖZET Yüksek lisans tezi olarak sunulan bu çalışmada 1995 Dinar depreminde orta derecede hasar gören betonarme bir binanın güçlendirme öncesi ve sonrasındaki lineer olmayan davranışı incelenmiş ve deprem güvenliği belirlenmiştir. Altı bölüm halinde sunulan çalışmanın birinci bölümünde konunun tanıtılması, konu ile ilgili çalışmaların gözden geçirilmesi, çalışmanın amacı ve kapsamı yer almaktadır. İkinci bölüm, betonarme çubukların lineer olmayan davranışlarının idealleştirilmesine ayrılmıştır. Bu bölümde, önce betonarmenin temel varsayımları verilmiş, daha sonra bileşik eğik eğilme etkisindeki betonarme kesitlerde iç kuvvet-şekildeğiştirme bağıntılarının ve bileşik iç kuvvet durumuna ait taşıma güçlerini ifade eden akma koşullarının nasıl idealleştirilebileceği açıklanmıştır. Üçüncü bölümde, betonarme uzay çubuk sistemlerde ikinci mertebe limit yükün hesabı ve göçme güvenliğinin belirlenmesi amacıyla geliştirilen ve bu çalışmada yararlanılan bir yük artımı yönteminin dayandığı varsayımlar, yöntemin esasları, matematik formülasyonu ve yöntemin uygulamasında izlenen yol açıklanmıştır. Yöntemde, düşey işletme yüklerinin bu yükler için öngörülen güvenlik katsayıları ile çarpımından oluşan belirli değerleri altında, aralarındaki oran sabit kalacak şekilde monoton olarak artan yatay yüklere göre hesap yapılarak incelenen sistemin limit ve göçme yükleri elde edilmektedir. Dördüncü bölümde, mevcut betonarme yapıların deprem güvenliklerinin belirlenmesinde izlenen yol ve betonarme yapı sistemlerinin rehabilitasyon yöntemleri gözden geçirilmiştir. Beşinci bölüm sayısal incelemelere ayrılmıştır. Sayısal incelemeler 1995 Dinar depreminde orta derecede hasar gören dört katlı betonarme bir bina üzerinde gerçekleştirilmiştir. Bu bölümde sözkonusu yapı sisteminin güçlendirme öncesi ve sonrası durumları ayrı ayrı ele alınmış, her iki durum için lineer olmayan sistem davranışları ve deprem güvenlikleri belirlenmiştir. Altıncı bölümde, bu çalışmada elde edilen sonuçlar açıklanmıştır. xıı
Özet (Çeviri)
SEISMIC CAPACITY ASSESSMENT OF AN EXISTING R/C BUILDING BEFORE AND AFTER STRENGTHENING SUMMARY The use of elastic-plastic analysis and design methods, which consider the non-linear behaviour of reinforced concrete as well as the non-linearity caused by geometrical changes may result in both more realistic and more economical solutions for reinforced concrete structures. Furthermore, by the use of these methods, the effects of various design and strengthening philosophies on the non-linear behaviour of reinforced concrete structures can also be investigated. In this study, a four-story reinforced concrete building structure moderately damaged during October 1,1995 Dinar earthquake is analyzed using a non-linear static (pushover) analysis method. Both material and geometrical non-linearities are considered in the analysis. The thesis consists of six chapters. In the first chapter, after introducing the subject and the related works, the scope and objectives of the study are explained. The main objective of the study is to evaluate and compare the seismic capacities of structural systems before and after strengthening. The second chapter outlines the non-linear behaviour of reinforced concrete frame elements. The investigation covers the actual internal force-deformation relationships, the yield (failure) conditions and the idealization of non-linear behaviour. This investigation of actual behavior of reinforced concrete elements is based on three basic assumptions, such as a- plane sections remain plain after bending, b- full bond exists between concrete and reinforcing steel, c- tensile strength of concrete is negligible after cracking. The non-linear behaviour of reinforced concrete frame elements under biaxial bending combined with axial force is idealized by the ideal elastic-plastic internal force- deformation relationships. This idealization corresponds to the plastic section concept with limited plastic deformation capability. When the state of internal forces at a critical section reaches the ultimate value defined by the yield (failure) condition, plastic deformations occur. The plastic deformations are limited to the rotational xiucapacity. The rotational capacity may be expressed in terms of the length of plastic region and the ultimate plastic curvature. In this study, an approximated yield surface which is composed of 24 linear regions is used for reinforced concrete elements subjected to biaxial bending combined with axial force. In the third chapter, the assumptions, the basic principles and mathematical formulation of the load increment method used in this investigation are presented and the corresponding analysis procedure is explained. The following assumptions and limitations are imposed in the development of the load increments method. a- The internal force-deformation relationships for reinforced concrete frame elements under biaxial bending combined with axial force are assumed to be ideal elastic-plastic. b- Non-linear deformations are assumed to be accumulated at plastic sections while the remaining part of the structure behaves linearly elastic. This assumption is the extension of classical plastic hinge hypothesis which is limited to planar elements subjected to simple bending. c- Yield (failure) conditions may be expressed in terms of bending moments and axial force. In this study, the effects of shear forces and torsional moment on the yield conditions are neglected. d~ The plastic deformation vector is assumed to be normal to the yield surface, for the case of biaxial bending combined with axial force. e- The second-order theory may be applied to the analysis of slender structures with high axial forces. In the second-order theory, the equilibrium equations are formulated for the deformed configuration while the effect of geometrical changes on the compatibility equations is ignored. f- Changes in the direction of loads due to deflections are assumed to be negligible. g- The structure is composed of straight prismatic members with constant axial forces. The members which do not meet these requirements can be divided into smaller straight and prismatic segments with constant axial forces. h- Distributed loads may be approximated by sufficient number of statically equivalent concentrated loads. In the load increments method used in this study, the structure is analyzed under factored constant gravity loads and monotonically increasing lateral loads. Thus, at the end of the analysis, the factor of safety against lateral earthquake loads is determined under the anticipated safety factor for gravity loads. xivWhen the gravity loads are known, the member axial forces can be easily estimated through equilibrium equations. Thus, the second-order effects are linearized by calculating the elements of stiffness and loading matrices for the estimated axial forces. In this method, the structure is analyzed for successive lateral load increments. At the end of each load increment, the state of internal forces at a certain critical section reaches the limit state defined by the yield condition, that is, a plastic section forms. Since the yield vector is assumed to be normal to the yield curve, the plastic deformation components may be represented by a single plastic deformation parameter which is introduced as a new unknown for the next load increment. Besides, an equation is added to the system of equations to express the incremental yield condition for the last formed plastic section. This equation is linear, because the yield surface is approximated to be composed of linear regions. Since the system of equations corresponding to the previous load increment has already been solved, the solution for the current load increment is obtained by the elimination of the new unknown. In the second-order elastic-plastic theory, the structure generally collapses at the second-order limit load due to the lack of stability. This situation is checked by testing the determinant value of the extended system of equations. If the magnitude of determinant is less than or equal to zero, the second-order limit load is reached. Hence, the computational procedure is terminated. In some cases, the structure may be considered as being collapsed due to large deflections and excessive plastic rotations. At each step of the load increments method, a structural system with several plastic sections is analyzed for a lateral load increment. In the mathematical formulation of the method, two groups of unknowns are considered, such as a) nodal displacement components, b) plastic deformation parameters at plastic sections. The equations are also considered in two groups. a) The equilibrium equations of nodes in the directions of nodal displacement components. b) The incremental yield conditions of plastic sections, which express that the state of internal forces at a plastic section remains on the yield surface during a load increment. xvIn the fourth chapter, the main procedures to be followed in determining the seismic safety of existing building structures that are built in earthquake zones, are explained. Also, this chapter outlines the repair and strengthening methods for rehabilitating the structures which do not have sufficient seismic safety imposed by the related codes and specifications. The main steps for determining the safety factor of existing structures are given below. 1) Obtaining and evaluating the documents related with the existing structure. 2) Observing the structure at site. 3) Modeling the existing structural system for analysis. 4) Analyzing the non-linear behaviour of the existing structural system. 5) Evaluating the factor of safety against earthquake loads. Rehabilitation process consists of all the repair and strengthening work done in order to increase the safety of the structure to an adequate level against external impacts. The repair methods for relieving various kinds of damage, construction defects and imperfections can be investigated under three main headings. These are, a) injections for cracks, b) repair of slight damages and imperfections on the concrete surfaces, c) repair of moderately and heavily damaged reinforced concrete elements. In practice, strengthening is used to increase the safety of the structure. The methods of strengthening are, a) jacketing, b) regional confinement with steel laminate, c) strengthening by adding new elements to the structure, cl) adding new shear walls to the structure, c2) infilling the frames with reinforced concrete walls. The structure selected for this analysis have been strengthened by infilling some of the frames of structure with reinforced concrete walls. The fifth chapter is devoted to the numerical investigations. The analysis procedure followed in this investigation consists of two phases, such as i) analysis of the existing structural system, ii) analysis of the structural system after strengthening. The structural data and the material characteristics representing the existing structural system are obtained through the examination of the inspection reports prepared by the teams of the Research and Application Center of the Istanbul Technical University. Furthermore, the soil profile and the seismicity of the surrounding area as well as the soil characteristics are given by the geothechnical investigation report. xviAccording to the geothechnical investigation report, the coefficient of effective ground acceleration and the characteristic spectrum periods of soil are determined as A"= 0.40 and TA = 0.20 sec, TB = 0.90 sec, respectively. The characteristic compressive cylinder strength of concrete is taken as approximately 10 Mpa according to the concrete test results conducted on the building. Class BÇI reinforcing steel with a yield strength of 220 Mpa is used in reinforced concrete elements. The cross-sectional dimensions and reinforcement of beams and columns are determined through the investigation of the original design project and inspection reports. The existing structural system is idealized as a space frame and analyzed by the non linear theory under constant vertical working loads and monotonically increasing lateral equivalent earthquake forces. The earthquake forces are determined in accordance with the new 1997 Turkish Seismic Code. The reduction factor for earthquake loads is taken as Ra = 4, to represent the ductility level of the existing structure. The existing building structure is strengthened by new shear walls arranged in both directions. New shear walls are constructed by infilling the existing reinforced concrete frames with reinforced concrete. In each direction, two new shear walls are added. The classes of concrete and reinforcing steel for newly added elements are BS20 (characteristic compressive cylinder strength of 20 Mpa) and BÇDI (yield strength of 420 Mpa). The strengthened structural system that is idealized as being composed of frames and shear walls in both directions, is also analyzed according to the non-linear theory under constant vertical working loads and monotonically increasing lateral earthquake forces. In the calculation of the lateral equivalent earthquake forces, a reduction factor of Ra = 5 is applied to the elastic loads, considering the relatively higher ductility level of newly added reinforced concrete elements. The existing and the strengthened structures are analyzed for earthquake loads acting in both directions. In each analysis, a) second-order limit loads and collapse loads, b) lateral load parameter versus lateral displacement relationships, c) total number of plastic sections and their distribution among beams, columns and shear walls, d) lateral load parameters for the first plastic sections developed in each type structural element are determined and compared. The following main conclusions can be drawn from the results of the numerical study. a) The ultimate lateral load parameter (ultimate lateral load carrying capacity divided by the working earthquake loads) for the existing structural system is increased xvnfrom 0.2858 to 1.8573 through strengthening. Considering the load and resistance factors imposed by the codes this level of safety is found to be higher than required. b) The plastic rotation capacities are exceeded before the limit load level is attained. The ratio of collapse load to limit load is 0.781 and 0.876 in Y and X directions respectively for the existing structure. The ratio takes the values of 0.912 and 0.908 for the strengthened structure. c) The number of beam plastic sections developed before the limit and collapse loads, increases substantially due to strengthening, resulting in higher ductility level of the structure. The sixth chapter covers the conclusions. The basic features of the investigation performed in the study and the general evaluation of numerical results are presented in this chapter. xvui
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