Conclusion
Seismic fragility of three common typologies of concrete moment frames, broadly categorized as frame with unreinforced masonry infill walls and those without infill walls are studied. Different configuration of masonry infill walls in the frame may sometimes render the frame highly irregular, for example, open ground story frames in which masonry infill walls are not provided in the ground story. Experience during past earthquakes suggests that the open ground story buildings behave poorly during earthquake shaking. Such buildings suffered severe damage in the ground story columns but no noticeable damage was observed in the upper stories. It is observed in the nonlinear time history analyses of the considered frames for six ground motions that the conventional engineering demand parameters (EDP), for example, top level displacement or drift, cannot capture this behavior of open ground story frames, and hence, the fragility estimated using such EDP will not be realistic.
The primary objective of the study is to establish an EDP that correctly interprets the behavior of irregular frames for fragility assessment. This is accomplished by considering both displacement and inter-story drift as engineering demand parameters for fragility assessment of regular and irregular frames. Equal importance is laid on the effect of infills and its presence or absence in the ground story of the frames. It is obviously observed in the fragility estimation that the absence of infills in the ground story makes the frame more vulnerable as compared to a frame without any infill in any story (bare frame). Further, a frame with infill walls in all the stories becomes vulnerable once the ground story infills fail, which otherwise, behaves as a regular frame.
