Seismic assessments for scoured bridges with pile foundations

•An integrated performance-based seismic assessment method is proposed.•For loose sand, the failure mechanism of a scoured bridge is transferred from the piers to the piles.•The seismic performance index of a scoured bridge increases at the initial scouring state.•Although scoured bridges have better seismic performances, they may have stability problems. To accurately estimate the seismic performances of scoured bridges with pile foundations, an integrated performance-based seismic assessment method is proposed in this paper. Nonlinear deformations of piers and piles are taken into consideration by using the concentrated plastic hinges at the bottoms of piers and the distributed plastic hinges with softened elastic modulus along the piles, respectively. The interaction between soil and pile foundation is modelled through four types of soil springs according to the design code. Seismic assessments of multi-span bridges with pile foundations are performed for different scour depths and soil properties using nonlinear static pushover analyses. Numerical results demonstrate that the seismic demands of bending moments and the locations of maximum moments for piles vary significantly with increasing scour depth. Compared with the fiber element method, the proposed distributed plastic hinges model with a softened elastic modulus can efficiently and accurately estimate the nonlinear deformation of scoured bridges. In addition, in the case of loose sand, the failure mechanism of a scoured bridge is transferred from the piers to the piles as the scour depth increases over a critical value. Finally, seismic assessments demonstrate that the seismic performance indices of scoured bridges increase with increasing scour depth with dense sand, while the seismic performance indices of scoured bridges decrease with increasing scour depth with loose sand when the failure mechanism is transferred. Although scoured bridges have better seismic performances, they may have stability problems.