Simplified analysis of dynamic response of pile-supported bridge under local scour and verification by centrifugal shaking tests

Scour causes the erosion of soil, changes the seismic response of site, and also influences the seismic properties of bridge. To investigate the dynamic behavior and damage potential of pile-supported bridges at local scour site, the effects of scour on the ground motion of site are firstly discussed, and a fast calculation method for calculating ground motion is presented. Next, a simplified model describing the bridge response is put forward, which considers the ground motion changes caused by local scour. Then the shear force at the pier bottom and pile head, and the maximum displacement of bridge are calculated by the modal superposition method so as to quickly evaluate the damage potential of bridge after scour and further determine the critical damage scour depth. Finally, the centrifugal shaking tests on the pile-supported bridge are conducted under 50g to verify the accuracy of this model. The superstructure of the bridge supported by 3×3 pile-group foundation is simplified as a mass block. There are 3 scour depth conditions. It is found that the site period obviously decreases under general scour, and hardly changes under local scour. The slope angle of local scour hole has virtually no impact on the ground motions of site. The motions at local scour sites are quite different from those at general scour sites, but similar to those at the original free site at the same depth. The scour depth, where the bridge reaches the greatest response, depends on the interrelation between bridge period and dominant frequency of the earthquake. The centrifuge tests further prove that the proposed model can be applied to the fast calculation of seismic response, the assessment of potential of scoured bridge and the critical scour depth under earthquakes.