Estimation of Loss in Global Lateral Capacity of MR-RC Frame in Risk Framework

Abstract

The lateral capacity of moment-resisting reinforced concrete (MR-RC) frames is a critical factor in their structural performance during seismic events. However, due to potential damage caused by earthquakes, these frames may experience a reduction in their original lateral capacity over time. Post-earthquake residual capacity assessment of a structure is needed for (i) making decisions about continued use of an existing structure after an earthquake, and (ii) designing a new structure to resist multiple earthquakes during its lifetime. However, residual strength in a structure can be defined in terms of reduction in withstanding ability of peak ground acceleration (PGA) due to mainshock and aftershock sequences. As earthquakes are uncertain events, and post-yield non-linear behaviour of a structure under seismic loading also consists of high uncertainties, performance assessment needs to be carried out to take effective decisions. A sequential Incremental Dynamic Analysis approach is used and analysis is performed in Open Sees, based on the combination of damage accumulated by mainshock signal with a set of aftershocks scaled in amplitude with respect to PGA. Different performance levels for structure such as immediate occupancy, life safety and collapse prevention, are decided based on member rotation limits described in American Standard Code. RC frame models having concentrated plastic hinges are developed in Open Sees. Aftershock fragility curves are drawn and collapse capacity of intact structure and already damaged structure gives an idea about the residual strength of structure for subsequent ground motions. Damage indices also helps in assessing seismic performance of structure under earthquake excitations and quantify structural damage at local and global level, its value ranges from 0 to 1, zero refers to undamaged structure and 1 means complete collapse of structure.