Seismic fragility curves for soft-storey buildings

Buildings with a soft-storey are notoriously vulnerable to collapse under strong earthquake shaking. However, a building subject to a small or moderate magnitude earthquake has a fair chance of survival depending on the drift demand on the softstorey. This paper presents fragility curves which define the probability of collapse of a soft-storey column when subject to a pre-defined drift demand. The calculation for the fragility curves is based on the estimated shear (frictional) resistance to slip along a major diagonal shear crack (which is the plane of weakness for collapse to occur). The fragility curves presented can be shown to provide a more realistic representation of the seismic vulnerability of the building than the conventional approach based simply on the degradation in the horizontal resistance of the column.