Damage assessment of deficient reinforced concrete setback structures

Abstract

The trend of adopting architectural designs with irregularities in elevation, meaning that the shape of the building is irregular, is on the increase. Seismically deficient structures are found in abundance in developing countries such as Pakistan, and structures with irregularities in elevation may result in failures due to sudden changes in stiffness, mass or strength along the building height. The aim of the work reported in this paper was to develop analytical seismic vulnerability curves for deficient mid-rise reinforced concrete building frames with setbacks. The vulnerability curves were derived by adopting a framework used in a previous study. Along with a regular frame, six-storey frames with different setback configurations were considered. The frames were modelled using the numerical analysis program Drain-3DX and their responses were estimated by generating force–displacement envelopes using non-linear static analysis. The response spectrum of the Uniform Building Code was used to impose a seismic demand. The hazard levels were evaluated at every point of the capacity envelope using a reverse procedure of Fema 440. The damage in the studied building frames was quantified through a direct correlation with the natural period of vibration of the buildings, as suggested in previous studies. The developed vulnerability curves showed brittle failure modes in seismically deficient buildings.