Sensitivity Analysis of Progressive Collapse of Steel Moment Frames Subjected to Blast Loading

It is becoming increasingly important to mitigate the effects of blasts by accidents or terrorist-campaigns on the structures. The explosive loading may result in large deformation of structural components thus endangering overall safety of the structure. Sometimes local failure of column(s) may cause disproportionate or progressive collapse of the structure if the beams and slab system in the affected zone does not offer sufficient tie strength to redistribute the loads. In the present paper, steel moment frames (SMF) of different plan shapes such as square, T and L are subjected to blast loading. The frames have been designed to resist gravity and seismic loads, but not blast loads or vehicle-bomb impacts. The blast loading with different parameters viz. charge weight and standoff distance, and position relative to the structure is considered. The blast loads are computed using empirical relations and charts available in the literature for determining coefficient of reflection. The blast loads are applied on the frames followed by conducting nonlinear static analysis. The probabilities of failure of SMFs due to the blast loading are investigated and the effect of uncertainties in blast parameters is assessed by plotting blast fragility curves. Sensitivity of fragility curves is also studied. Probabilistic analysis is carried out using Monte Carlo (MC) simulations. Few remedies to protect steel frames vulnerable to progressive collapse are discussed.