On the Influence of Unexpected Earthquake Severity and Dampers Placement on Isolated Structures Subjected to Pounding Using the Modified Endurance Time Method

The aim of this study is to investigate the performance of isolated structures by considering the possibility of impact under severe earthquakes. In the design of isolated structures, the required displacement capacity is determined based on the considered earthquake hazard level. However, there is a possibility of an impact caused by moat walls or adjacent structures under severe earthquakes. Dampers are used in this study to improve the performance of structural and nonstructural components. In this regard, three isolated structures (6, 9, and 12 stories) equipped with Triple Friction Pendulum Isolator (TFPI) are designed under earthquake hazard levels of BSE-1 with return periods of 475 years. Based on the different positions of these three structures relative to each other, four scenarios are defined to investigate the effect of impact. Modified endurance time (MET) method, as a cost-efficient nonlinear time history analysis method, is employed for structural evaluation under variable earthquake hazard levels. The placement of dampers is also taken into account in evaluating the effect of dampers. Therefore, the structures have been retrofitted once by adding damping and stiffness devices (ADAS) on the stories and once by adding fluid viscous dampers (FVD) at the isolated level. Results indicate that structures might collapse under earthquake hazard levels of BSE-2 with return periods of 2475 years. This matter is influenced by the adjacency of two isolated structures next to each other, and the severity of this fact depends on the height of the structures and the displacement capacity of the isolators so that the tall, isolated structures have decreased the performance of the adjacent shorter isolated structure. Moreover, the placement of dampers has a significant influence on the performance of structural and nonstructural components, depending on the reason for the impact.