Improving the performance of a reinforced concrete building with seismic isolation according to the Building Code of Turkey - 2017

In recent years, urbanization and number of buildings have increased so much that national economies can seriously be affected due to structural damages in residential and commercial buildings after natural disasters such as earthquakes. It is obvious that it can cost too much to pay for maintenance or retrofit of structures considering the life cycle cost. Moreover, it is very important to prevent structural damages because any loss of life is irreversible and irrepleaceable. Due to new generation computers and softwares, it is easier to analyse complicated structures whose analysis requires too much memory. This leads up innovative methods of structural design. Similarly, structural performance concept which is also counted as a measure of structural damage gained importance in recent years with the help of computers which has ability to analyse detailed structures. Either assesment and retrofit of existing structures or performance based design of structures can be applied in a more effective way. In the fixed base or conventionally retrofitted structures, the energy of strong ground motion is dissipated by the enery of deformation of structural and non-sructural elements. Structural damping is quite crucial about energy dissipation and it is provided by deformation of structural and non-structural elements. In case of a high demanding earthquake, it is reasonably possible that the related deformations cause serious damage. It is possible to save people's lives and property with base isolation whose goal is to prevent structural damage during earthquakes or other big natural disasters. Thus, it is easier to provide immediate occupancy or operational performance level in structures during and after earthquakes. In this study, it is aimed to improve the performance level of a fixed based 8-storey reinforced concrete building applying seismic isolation at the base level. The seismic isolator in this study is friction pendulum. Due to seismic isolation, it is aimed to prevent structural damage. The structure in this study is assessed according to the Building Code of Turkey - 2017 which was published in official gazette on 18th March of 2018. The existing structure has the performance level of "life safety" under DD-2 design earthquake whose exceedance probability is 10% in 50 years (475 years of return period). It is aimed that the performance level of the structure has "operational performance level" applying sesimic isolation under the same design earthquake. This study consists of six parts. The first part of six explains subject, purpose and content of the study. In the second part, basic principles of structural design with seismic isolation are explained. Seismic isolation types which are applied in general and feasibility of seismic isolation are referred. The concept of seismic isolation is explained examining throughout its own historical development. Design principles in the Building Code of Turkey – 2017 and current application types of seismic application and device types. Also mechanical properties of friction pendulum devices and literature research are handled in the second part. In the third part, principles of seismic assessment of buildings in the Building Code of Turkey – 2017 are explained in detail. Within this scope, the principles which are taken into consideration for nonlinear time history analysis under earthquake loading and seismic performance assessment of both the existing and the seismically isolated structure are explained. Also, material models and section analysis are explained in this section. In the fourth part of the study, time history analysis steps under earthquake loading are explained. Initially, geometrical properties of the existing structure are explained in general. After explaining material and section properties, section analysis results are given. According to the section analysis results, plastic hinge modelling steps are explained. Either dead and live loading or seismic loading with nonlinear time history analysis method are explained. Also, loading steps are defined as well. The analysis results take part in the fifth part of the study. In order to compare the analysis results and assessment of existing structure, pushover analysis are run for both fixed based structure and the isolated one. Modal capacity curves are superposed and compared to realize the global behavoir of both structures. Seismic performance assessments of existing and seismically isolated structure are reported in the fifth part of the study. For earthquake loading, 11 pairs of ground motion acceleration records are used according to the Building Code of Turkey – 2017. Each ground motion record is applied in both horizontal directions. So average of 22 analysis results are used for each structural element. Damage levels in structural elements under seismic loading are determined according to plastic rotation in critical sections. In order to run earthquake analysis, non-linear time history anaysis method were employed. For each performance assessment and design process, ground motion datas were scaled according to related spectrum and period interval. The results were summarized with graphics and tables. In addition, structural elements are checked for shear forces according to the Building Code of Turkey – 2017. Not only base shear check under DD-2 design earthquake level but also every friction pendulum device is checked for shear forces as well. Under DD-1 design earthquake level, displacement check of seismic isolation system is made. In the sixth part os the study, nonlinear time history analysis results are compared and discussed. Also, modal capacity curves which are obtained from nonlinear static pushover analysis are superposed and compared. The difference in structural behavior with seismic isolation is studied. Analysis and assessment show that the base shear force in the seismically isolated building is 70% level of which in the fixed based building. Interstory drift ratios are compared for each horizontal direction as well. The greatest interstory drift ratio was occurred in the third storey level in the fixed based structure. On the other hand, the greatest interstory drift ratio was occurred in the first storey level in the seismically isolated structure. The biggest interstory drift ratio difference between two buildings occurred in the third storey level. The greatest interstory drift ratio in the seismically isolated building is about 0.0035hi which is under the upper boundary for "operational performance level" (0.005hi). According to the results of nonlinear static pushover analysis, seismically isolated building produces higher spectral displacement and lower spectral acceleration.