Blast Resistance Capacity of Seismically Designed Building Frames

Abstract

Because of the inherent uncertainty in the blast loading caused due to terrorist attacks, most buildings are not designed for blast loading, but they are routinely designed for earthquake demand. If the blast resistance capacity of the seismically designed building can be evaluated, the risk of the blast loading caused due to the terrorist attacks can be reduced by upgrading the seismic design of the building. With this background in view, the present paper investigates the blast resistance capacity of a 6 storey building frame designed for extreme peak ground acceleration (PGA) levels of 0.5g, 0.4g, and 0.3g. The 3D model of the 6 storey building is designed according to Indian Standard (IS) codes for the above mentioned extreme level earthquake. Designed buildings are subjected to surface blast of 500 kg of TNT(trinitrotoluene) at different standoff distances ranging from 5m to 30m. The time histories of the blast loading due to air pressure and ground shock are modeled by those existing literature. A nonlinear time history of analysis (NTHA) of the frame is performed in SAP 2000 for surface blast and the simulated earthquakes from the specified response spectrum in IS code. NTHA results for both cases are compared to evaluate the relative performance of the three different seismically designed buildings to the surface blast loading. The response quantities of interest include maximum drift, maximum top displacement, and number of hinges formed. The results of the study indicate that for the near blast conditions the blast resistance capacity of the building increases with the increase in the PGA values for which the building is designed. By upgrading the seismic design by 0.1g, the blast resistance capacity increases manifold for near blast conditions. Thus, by updating the seismic design of a building, the risk of blast loading in the design may be considerably mitigated.