Pounding Probability of Three-Span Simply Supported Bridge Subjected to Near-Field and Far-Field Ground Motions

During earthquake shaking, pounding of decks occurs in multi-span simply supported bridges (MSSS) when relative displacement between two adjacent decks exceeds the available expansion gap. It may cause the failure of a bridge in various ways such as unseating of the deck, pier failure, bearing failure, and local damage to decks and girders. The damage level of bridge also depends on the distance of the bridge from the fault rupture because the properties of ground motion change with distance from the fault rupture. This paper focuses on pounding probability of a three-span highway bridge subjected to three different types of ground motions, namely, near-field ground motion with pulse, near-field ground motion without pulse, and far-field ground motion along the longitudinal direction of the bridge. Finite element analysis of the bridge was performed in OpenSees considering the nonlinear behavior of piers and bearings. Energy dissipation during pounding of decks was also considered. Incremental dynamic analysis (IDA) was performed to obtain the level of earthquake shaking (i.e., peak ground acceleration (PGA)) required for pounding between adjacent decks. Based on the IDA, fragility analysis was performed to obtain the pounding probability of decks. At a particular PGA level, it was found that far-field ground motions resulted in higher pounding probability as compared to near-field ground motions. When gap size was small, pounding probability for near-field ground motion with pulse was found to be smaller than that of near-field ground motion without pulse. However, when the gap size was large, near-field ground motion with pulse caused higher pounding probability as compared to near-field ground motions without pulse.