Effect of slab bottom reinforcement on seismic performance of post-tensioned flat plate frames

The purpose of this study is to evaluate the seismic performance of gravity-designed post-tensioned flat plate frames with and without slab bottom reinforcement passing through the column. In low and moderate seismic regions, the seismic demands may not control the design, and buildings are often designed considering only gravity loads. This study focuses on the seismic performance of gravity load designed post-tensioned flat plate frames. For this purpose, three-, six- and nine-storey post-tensioned flat plate frames are designed considering only gravity loads. For reinforced concrete flat plate frames, continuous slab bottom reinforcement (integrity reinforcement) passing through the column should be placed to prevent progressive collapse; however, for the post-tensioned flat plate frames, the slab bottom reinforcement is often omitted since the requirement for the slab bottom reinforcement for post-tensioned flat plates is not clearly specified in ACI 318-05. This study evaluates the seismic performance of the model frames by conducting non-linear static pushover analyses and non-linear response history analyses. For conducting non-linear response history analyses, six sets of ground motions are used as input ground motions, which represent two different hazard levels (return periods of 475 and 2475 years) and three different locations (Boston, Seattle and Los Angeles). An analytical model is developed for emulating the non-linear hysteretic behaviour and the failure mechanism of post-tensioned slab–column connections. This study shows that gravity-designed post-tensioned flat plate frames have some seismic resistance. In addition, the seismic performance of post-tensioned flat plate frames is significantly improved by placing slab bottom reinforcement to pass through the column.