Seismic safety of structures: Influence of soil-flexibility, asymmetry and ground motion characteristics

Structures may experience degradation in strength in the event of strong seismic shaking. A rational estimation of the reserve strength of the structures is often desired in the process of retrofitting or strengthening the same. To achieve this end, the present paper confirms the suitability of an existing hysteresis model in reproducing experimental load–displacement characteristics for reinforced concrete (R/C) structural members. Attempt has also been made for rational and realistic estimation of the degradation parameter required for the model in absence of any case-specific calibrated value. Subsequently, post-earthquake behaviour of the low-rise symmetric structures is assessed with and without accounting for the effect of soil–structure interaction. Such response for low-rise multistorey systems with regular asymmetry has also been investigated in the sample form. To develop insight into the behaviour of asymmetric (uni-directional and bi-directional) systems, detailed investigation has been made on idealized single-storey asymmetric systems under simulated and real ground motions with different phase difference or time lag variation. This suggests a serious implication of occurrence of peaks of the ground motions on the seismic performance of bi-directionally eccentric structures and indicates a relatively higher torsional vulnerability of bi-directionally eccentric system compared to equivalent uni-directional counterpart. The results along with the endeavour toward measuring the ductility capacity for R/C structural members based on the systematic observation and interpretation of the available experimental results, made in the paper, may prove useful in evaluating the seismic safety of low-rise R/C structures.