Widening of Existing Motorway Bridges: Pile Group Retrofit versus Nonlinear Pile

Widening of Existing Motorway Bridges: Pile Group Retrofit versus Nonlinear Pile–Soil Response

Sakellariadis, L. / Marin, A. / Anastasopoulos, I.

Modernization of motorway infrastructure often involves widening of existing bridges which need to be retrofitted to sustain the increased loads. Whereas pier retrofit is relatively straightforward, pile group strengthening can be a challenging, costly, and time-consuming operation. Such major operation can be avoided by taking advantage of nonlinear foundation response. Within this context, the paper presents a comparative assessment of current practice, based on elastic foundation design, and of an alternative design approach that allows nonlinear foundation response. This allows for the exceedance of the conventionally defined (elastic) moment capacity of the foundation through load redistribution between piles during seismic shaking. Inspired by the widening of a Swiss bridge, a numerical study is conducted employing three-dimensional (3D) finite-element (FE) modeling. The analysis compares the widened bridge with retrofitted versus unretrofitted foundation. For moderate design-level seismic shaking, the performance is almost identical. For stronger shaking substantially exceeding the design limits, the unretrofitted foundation is advantageous because it reduces structural damage by dissipating energy through soil yielding, at the cost of increased—but totally tolerable—settlement.