Performance-based seismic design of rocking shallow foundations in cohesive soil: Methodology and numerical validation

Abstract

The concept of rocking shallow foundation as a base isolation mechanism has been incorporated into seismic design guidelines, but a feasible design method is yet to be developed. This research proposes a performance-based seismic design (PBSD) for bridges supported on rocking shallow foundations in cohesive soils. This PBSD considers three performance indicators: maximum drift, residual footing rotation and residual settlement. Empirical correlations to obtain the secant stiffness, hysteresis damping ratios, re-centering ratio and residual settlement were obtained from preceding field tests. The PBSD was elaborated with two examples for which the shallow foundation of an as-built highway overpass bridge was re-designed in two presumed cohesive soil sites. The performance of the re-designed bridge was further verified using nonlinear time history analyses. A numerical model was developed, calibrated, and validated using field test results. The maximum and residual drifts and residual footing settlement at the design level earthquakes obtained from numerical modeling were shown to satisfy the performance criteria.