Seismic performance of strength degraded structures

Traditionally, performance assessment of a structure is based on trading off strength demand with ductility demand. In high seismicity region, the design provisions are based on the concept of conservation of energy; such guidelines (FEMA 273) recommend a very low drift capacity for strength degraded structures. Furthermore, the application of these guidelines, results in most of the strength degraded structures deemed unsafe when subjected to earthquake excitations in low and moderate seismic regions. This paper presents results of nonlinear time history analyses (THA) for such strength degraded structures for a range of near-field and far-field earthquake scenarios of different M-R combinations. Fragility curves defining probability of failure of structures have been developed. The insensitivity of the probability of failure of the URM wall on its height (i.e. vertical span length) is an interesting finding in this study. Also, the extent of strength degradation in an unreinforced masonry wall is not shown to have increased its probability of failure.