Progressive collapse mitigation approaches for steel-concrete composite buildings

This paper investigates the robustness of steel-concrete composite frames under sudden column loss. Various lateral load resisting systems, including contributions from bracing systems, composite slab and joints are taken into account in analysing buildings against progressive collapse. Robustness of ten-storey steel buildings with (1) diagonal braces at corners, (2) centre core wall, (3) rigid moment joints are analysed for corner, perimeter and internal column loss. The analyses conclude that simple braced frames are more susceptible to the progressive collapse compared with the moment resisting frames which has higher redundancy to redistribute the loads arising from sudden column loss. Various mitigation approaches are proposed to improve the progressive collapse resistance of the simple braced frames. End-plate beam-to-column connection is proposed instead of fin-plate connection due to greater rotational stiffness and higher moment resistance. Vierendeel truss is proposed at the top floor level in a multi-storey building to redistribute the load due to sudden column loss. In addition, modified fin-plate connection is proposed in which a plate is welded to the bottom beam’s flange to increase joint’s rotational restraints helping to reduce beam’s vertical displacement in the event of sudden removal of column.