Evaluation of seismic anchor systems in bridges: performance under multidirectional seismic loads

This study evaluates the effectiveness of seismic anchor systems—namely, vertical seismic bars and pre-tensioned cables—in mitigating uplift and controlling displacements in bridges subjected to both horizontal and vertical seismic loads. Time-history analyses were conducted using detailed three-dimensional nonlinear models to assess the performance of different anchor configurations under various seismic scenarios. Seismic records were carefully selected to capture maximum demands in either the horizontal or vertical direction, with corresponding components applied to represent the seismic demands accurately. The analysis focuses on the role of prestressing levels in cable-based anchors, examining how they influence the reduction of uplift and control of horizontal displacements. Fragility curves were developed to quantify the probabilities of damage for different anchor configurations. The results demonstrate that both seismic bars and prestressed cables significantly reduce uplift at high-intensity levels, with prestressed cables at 50% of their yield strength offering the most effective solution. Increasing prestress levels beyond 50% yielded minimal additional improvement. Furthermore, vertical anchors enhance the connection between the bridge superstructure and substructure, reducing the probability of damage due to horizontal displacement, though they also increase the forces transmitted to the columns.