Progressive Collapse Potential of Steel Frames Sustaining Post-Hazard Support-Yielding

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Abstract

Hazards such as fire, blast or severe seismic event may cause a local failure of columns leading to disproportionate or progressive collapse of a structure. Progressive collapse is a complex dynamic process greatly influenced by several factors including the integrity and tie-strength of beam-and-slab system over the damaged column, load-redistribution mechanism and post-hazard-exposure condition of the columns’ bases. In the present study, simple steel space frames designed conventionally as per Indian standard codes of practice are considered for numerical parametric study. Column removal locations as recommended by Unified Facilities Criteria (UFC 4-023-03) are considered. Progressive collapse potential is assessed for different column sections subjected to loss of major load-bearing element while adjoining columns have partially lost their fixity with the base. This is modelled by varying support conditions as fixed, hinged or roller; whilst joints adjacent to the lost column are changed to pinned connections. The effect of material properties degradation is also evaluated considering variation in steel grade. The progressive collapse potential is seen to be higher for frames with yielded supports emphasizing that the static indeterminacy plays an important role in progressive collapse potential of frames. Amongst the steel sections considered herein, square-section columns are found to be the most effective against progressive collapse.