Performance-based seismic evaluation and nonlinear behaviour of multistorey steel structures

The safe and economical desing of structure in earthquake regions is closely related to the knowledge of the nonlinear behavior and ductility of structural systems. Along with the reinforced concrete structures, this is also true for multistorey steel structures which have become more in recent years. When results of strong earthquakes, that took place in our country which is sited in a zone of high seismicty, are studied, it is clearly seen that level of damage on structures is high and loss of life caused by structural damage is great. When these consequences are considered, the first aim of earthquake engineering is to endure earthquakes without having too much structural damage that will be the cause of human loss. Among studies conducted to achieve this goal, the evaluation of earthquake safety of existing structures by performance based analyses takes the firs place. Building systems under earthquake forces can be investigated by two approaches as linear an nonlinear analysis. Because nonlinear analysis methods are more complex than linear analysis methods and analysis is time comsuming, in building codes nonlinear behaviour of building structures are tried to be taken into consideration indirectly. Recently, nonlinear analysis become easier and more practical, regarding to speed of computers, development of computer analysis methods and programs. The developments in material science has helped engineers to understand the material characteristics of components of the structures systems beter and implementation of these characteristics in structural calculations also assists in the developments of the nonlinear anaysis methods of structural systems. Regarding these points, in this study, which is presented as a Master of Science Thesis, steel frame model selected to represent the multistorey steel structures is designed and analysed regarding to the 2006 Turkish Seismic Code (DBYBHY-06) and Building Code for Steel Structures (TS 648). By design for Z2, Z3 and Z4 soil profile types defined at seismic code, six different systems are investigated by considering and omitting drift boundaries. To find the performance points and to do displacement performance appraisal of these systems, seismic code is used, components performance levels are determined by FEMA 356, and parameters regarding nonlinear behavior are calculated by ATC 19. It is believed that conclusions obtained by the numerical analyses of the study will prove useful to designers and provide a reference against which other researchers can compare their results. Keywords: Multistorey steel structures, linear analysis, pushover analysis, performance based design, ductility ratio, response modification factor.