Vulnerability of Buildings with Flat Plates and Flat Slabs to Progressive Collapse

Abstract

The investigation of progressive collapse of buildings has been of special interests during the last decade. The aim of this study is to assess the influence of selected design parameters on the vulnerability of structures with flat plates or flat slabs to progressive collapse triggered by the severe damage or failure of a column as a result of accidental or maliciously intended terrorist activity. The variables of frames with two-way slab systems investigated include: the number of stories in buildings (low-, medium- and high-rise buildings), span ratio (the ratio of span lengths in two orthogonal directions), span length for square panels, as well as the effect of having flat plates compared to flat slabs detailed either as ordinary gravity load carrying systems or by following the seismic detailing requirements of the Canadian practice as per CSA A23.3-04.

The linear-elastic static analysis method, outlined in the General Services Administration (GSA) guidelines of the US, was employed to conduct a parametric investigation to assess the significance of the design variables considered on progressive collapse potentials of buildings. This involved the computation of demand/capacity ratios (DCR) Higher DCRs were obtained for buildings with increased number of stories and span ratios, while the change in span lengths did not show a clear trend. Also, flat slabs were less vulnerable, and experienced smaller DCRs, than flat plates. Buildings detailed according to the seismic provisions of CSA A23.3-04 were less vulnerable than those detailed without these provisions. However, both slabs with non-seismic and seismic detailing required improvements in terms of the percentage of top and bottom reinforcement and bar lengths, depending on the slab type and the design parameters considered.