Progressive collapse resistance of steel framed buildings under extreme events

Abstract

This paper presents experimental and theoretical investigations on the progressive collapse behavior of steel framed buildings subject to extreme loads such as blast, impact, and fire. A new bearing capacity-based index is proposed to quantify the robustness of structures. An energy-based theoretical model is also proposed to quantify the effect of reinforced concrete slabs on the collapse resistance of structures. The experimental results show that the dynamic amplification factors of frames subject to impact or blast are much smaller than the conventional value of 2.0. The collapse process of frames in fire can be either static or dynamic depending on the restraint conditions and load levels. It is important to consider the failure time and residual strength of blast-exposed columns for assessing the collapse resistance of structures subject to explosion. Two collapse modes of steel frames under blast or impact are found: connection-induced collapse mode and column-induced collapse mode. In case of fire, a frame may collapse due to either column buckling or pull-in effect of beams. The energy dissipation due to the elongation of slab reinforcement and additional resultant bending moment considerably contributes to the collapse resistance of structures.