Reliability of bridges under near-fault pulse-type ground motions with vertical component consideration

Seismic waves from near-fault earthquakes often produce pronounced pulse effects, significantly influenced by vertical ground motion. This study investigates the seismic response of bridges under near-fault pulse-type ground motions (NFPTGMs), emphasizing the vertical component, and proposes a conceptual passive vibration control solution. A dataset of 100 NFPTGMs is used for three-dimensional nonlinear time history analyses of short/medium-span beam bridges and long-span suspension bridges. Plastic hinges are modeled in piers to simulate realistic damage, and seismic performance is evaluated by comparing peak moment responses to bending resistance derived from axial load-bending moment interaction domains. Statistical analysis produces fragility curves, revealing that the vertical component substantially increases the probability of exceeding damage thresholds. To mitigate seismic vulnerability, a 3D tuned mass damper (TMD) is proposed, positioned on the pier for beam bridges and the tower for suspension bridges. The TMD’s parameters are optimized using a genetic algorithm to minimize lateral deformation while accounting for vertical excitation. Results demonstrate that the optimized 3D-TMD achieves over 60 % reduction in peak moment responses for both bridge types. This solution offers a practical and effective approach to reduce seismic risk and enhance bridge resilience in near-fault regions, addressing the critical role of vertical ground motion.