Assessment of Deficient Reinforced Concrete Structures with Vertical Setbacks Subjected to Sequential Earthquakes

Abstract

Devastating earthquakes have previously occurred in Pakistan, causing enormous damage. Pakistan is a developing nation, and the country's low to mid-rise building construction practices are inadequate, sticking to conventional methods and using structural members for buildings that are either poorly detailed or not seismically designed, making them seismically deficient. Also Due to architectural requirements, structures with vertical setbacks throughout the height are becoming more prevalent. It is standard procedure for engineers to design the structures for the primary shock of a building that is initially undamaged, ignoring the successive shocks that may pose a risk to structures that have already experienced the main shock-induced loss of strength and stiffness. This study aims to assess the performance of deficient reinforced concrete structures with vertical setbacks subjected to sequential shocks using the CSI ETABS and following the performance-based analysis guidelines provided by FEMA 356. In this study various structures of 4 and 6 stories with different setback configurations were analyzed by NL-Pushover and NL-time history analysis, furthermore, buildings were also subjected to sequential shocks to predict the response against sequential shocks. This study shows that damage induced to frames by main shocks was further worsened by the application of sequential shocks, also, setbacks induced concentration of forces and deformations at the point of irregularity. The damage quantification was carried out in terms of performance points, ISDR, plastic hinge formation, and stiffness degradation