Lateral Capacity Model for Backfills Reacting against Skew-Angled Abutments under Seismic Loading

Abstract

Presence of skew-angled abutments complicates the seismic behavior of ordinary bridges, primary effect of which is the passive lateral resistance of the engineered backfill behind the abutment. The eccentricity of the soil reaction relative to the bridge’s center of stiffness or mass causes a skew bridge to rotate under seismic excitations, and a nonuniform soil pressure distribution develops behind the abutment backwall. A distributed nonlinear spring model is devised to represent the lateral passive reaction of the backfill soil. The behavior of these springs is based on a model that was previously developed and experimentally validated for straight abutments, dubbed the log-spiral hyperbolic (LSH) model, which is modified herein by a scaling factor that is based on the skew angle. This new modeling approach is verified against three-dimensional finite element model simulations and is validated with data from five prior large-scale experiments that produced direct measurements of load-deformation backbone curves for several skew angles. In the final step, the validated modified [i.e., skew-LSH (SLSH)] model is used in parametric studies to devise a simple bilinear load-deformation relationship that is parameterized with respect to backwall height, abutment skew angle, and backfill soil properties. This simple relationship is intended for routine use in the capacity-based seismic design and analysis of skew bridges.