Seismic Performance of Aged Suspension Bridges in California

This study examines the performance of a steel suspension bridge located in California and subject to the combined effects of near-field ground motions and aging under different environmental conditions. The analysis is conducted on a detailed numerical model of a long-span steel suspension bridge developed in OpenSees, incorporating both material and geometric nonlinearities. Aging effects resulting from corrosion are incorporated into both the material properties and geometry of the bridge sections, and three environmental conditions with different corrosivity levels are considered (medium, high, and very high). Empirical corrosion models are utilized to account for sections’ thickness loss and mechanical degradation of steel after 75 years of exposure, representing the code-compliant design service life. Seven near-field ground motions with directivity and fling-step effects are then selected and nonlinear time-history analyses are carried out to assess the seismic performance of the bridge for each corrosivity level. Results are compared with those obtained from the same bridge without corrosion. Findings of this study demonstrate the adverse effects of aging on the seismic performance when corrosion is included, especially for harsh corrosivity conditions. It is also observed that the capacity and deformation demands of the bridge would be underestimated if aging is neglected.