Energy analysis of progressive collapses in a multi-span bridge under vessel impact using centrifuge modelling

•Vessel collisions may lead to progressive collapses in a multi-span bridge.•Energy transfer and dissipation among bridge piers is quantified through centrifuge modeling.•The mechanism of one failed pier triggering progressive collapses of the entire bridge system is revealed.•Influences of foundation scour on the energy evolution are quantified.•Mitigation measures against progressive collapses of multi-span bridges are suggested from the energy perspective. Bridges spanning busy coastal or inland waterways are exposed to high risks of accidental vessel collisions. When a multi-span bridge is impacted, progressive collapses may develop within the bridge system, which can be aggravated by a decrease of pile embedment depth due to scour. Yet the system responses of multi-span bridges supported on pile foundations under vessel collisions are not well understood in the literature. Based on two series of advanced centrifuge tests on a three-pier bridge system at normal and scoured conditions, the energy transfer and dissipation in the bridge system during vessel impacts is systematically investigated in this study. During collision, 8–40% of the kinetic energy of the vessel is transferred to the bridge-soil system. The pier that is directly struck by the vessel absorbs 60–80% of the transferred energy. One pier fails when the input energy exceeds its limiting energy dissipation capacity. After failure, the energy redistributes to the adjacent piers, causing progressive collapses. From the energy perspective, mitigation measures for preventing progressive collapses of multi-span bridges should include decreasing the transferred energy, increasing the energy dissipation capacity, minimizing foundation scour, and cutting off the energy transfer path.