Ultimate Drift at Gravity Load Collapse of Non-ductile RC Columns
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 can be overly conservative for evaluating seismic performance of buildings supported by non-ductile columns. This is because lateral strength of such columns could be rapidly degraded and consequently the columns are deemed collapse at very low drift although they still can safely carry their gravity load. In this study, the drift capacity is defined as the drift at which the column can no longer sustain gravitational loading. Six column specimens representative of current construction practices in Thailand were tested under cyclic loading. All columns have identical cross-sectional and axial load properties but different shear span-to-depth ratios and splice detailing. The experimental results showed that shear failure associated with rapid lateral strength degradation could be observed in short columns whilst long columns are failed in preferable flexure mode. In spite of the rapid loss in lateral strength, the limiting drift of the short columns are almost identical to the long one (4 -4.5% drift). The test also revealed that the presence of lap-splice in plastic hinge region causes the lateral strength to degrade rapidly but surprisingly increase the plastic hinge rotation and the drift at axial collapse. The experimental results will be further used to develop an accurate deformation model which will form part of the displacement-based methodology for the seismic performance assessment of buildings.