Seismic risk assessment of bridges based on vulnerability analysis and tolerance theory

This study proposes a seismic risk assessment framework for bridge structures from an economic-risk perspective, integrating vulnerability analysis and risk-tolerance theory. A multi-dimensional damage-state space is constructed to quantify structural risk levels under varying seismic scenarios. The framework employs risk-tolerance theory to classify structural responses into defined risk intervals during earthquakes. Applying this methodology to quasi isolated, simply supported girder bridges designed in accordance with Chinese bridge design codes yields the following key insights: (1) Bridges detailed by standard specifications demonstrate seismic risks that remain within broadly acceptable limits, with no scenarios exceeding intolerable thresholds; (2) Seismic risk decreases as pier height increases. However, beyond critical pier heights of approximately 20 meters, the marginal risk reduction from further height augmentation diminishes significantly, necessitating a trade-off between safety and economy in design optimization. (3) At shear-key strength ratios exceeding 0.2 (20% of superstructure dead load), structural risk stabilizes but shifts damage concentration to piers, exacerbating their vulnerability. At ratios below 0.15 (15%), quasiisolation effects dominate, confining pier damage to repairable levels and maintaining risk within publicly acceptable bounds. By translating structural performance into clear risk metrics, this framework equips non specialists with intuitive, socio economically informed indicators, thereby advancing performance based seismic assessment practices.