ABSTRACT
The ultimate drift capacity of a lateral load resisting element is usually defined by the conditions at which the maximum lateral load resisting capacity is reduced to 80% of the design strength. This definition for the ultimate drift capacity can be overly conservative in conditions that are characterised by displacement-controlled seismic behaviour as illustrated with the case study of a soft-storey building. In such conditions, the ultimate drift capacity of the soft-storey column is defined as the drift at which the column could no longer sustain gravitational loading. This paper is concerned mainly with the ultimate behaviour of columns with low aspect ratios and poor confinement conditions. Failures of such column when subject to lateral loading is characterised by the development of shear cracks. Failure surfaces on both sides of the crack are liable to slip and result in column failure if resistance to slip (attributed mainly to aggregate interlock) is overcome by gravitational loading. Failure will eventually occur as the shear crack gradually widens with increased displacement of the column. The proposed model provides a reliable prediction of the displacement limit at which the gravitational load-carrying capacity of the column could not be maintained. The force-displacement behaviour of the column up to this limit is also modeled.
