Blast Load Effects on Highway Bridges. II: Failure Modes and Multihazard Correlations

Bridges with different seismic design levels and concrete compressive strengths have been analyzed for three levels of underdeck blast loads. It is observed that there are several other damage modes besides failure of bridge columns that may contribute to a complete collapse of the bridge. In general, it is demonstrated that an increased seismic resistance leads to improved performance during blast loads. Both concrete strength and seismic capacity are equally effective for bridges designed with higher seismic resistance. Extensive simulations have been performed to establish a correlation between the ratio of ductility and strength reduction factor, μ/R, and pier top displacement for concrete with different compressive strengths. It has been observed that the pier top displacement decreases drastically for μ/R>6. Moreover, it is observed from results of 27 simulations that bridge piers with μ/R>6 survive high levels of blast loads (without failure of piers).