Assessing the seismic performance of bridges in Metro Vancouver under M9 Cascadia subduction zone earthquakes with explicit consideration of basin amplification effects

The Metro Vancouver region of southwestern British Columbia could experience Magnitude 9 (M9) Cascadia Subduction Zone (CSZ) earthquakes. The seismic hazard of the region is further exacerbated because sits above Georgia sedimentary basin, which can amplify earthquake ground motions. Given the critical role of bridges as essential nodes within the transportation network, it is important to assess the potential impacts of such seismic events on these structures. This thesis evaluates the seismic performance of bridges within the Metro Vancouver region under plausible M9 CSZ earthquakes, with explicit consideration of the amplification effects of the Georgia basin. An inventory of more than 200 bridges was assembled by collecting as-built drawings. The detailed properties of approximately 80 bridges were extracted, with the focus on bridges supported by reinforced concrete (RC) circular columns and rectangular walls. Detailed bridge data was used to develop Single-Degree-of-Freedom (SDOF) models to characterize bridge response by following five key steps: (1) determination of bridge weight, (2) estimation of bridge stiffness, (3) evaluation of lateral strength, (4) definition of a material model to characterize nonlinear response, and (5) SDOF model assembly with the corresponding weight, stiffness, strength and calibrated material model to simulate the force-deformation behavior of the bridge. Nonlinear time history analyses were carried out to evaluate the response of each bridge under 30 physics-based ground motion simulations of M9 CSZ earthquakes adjusted for the corresponding soil conditions at each site. The results indicate that bridge damage correlates well with basin depth, with 33%, 48% and 92% of probability of complete damage, on average, for bridges outside the basin, in the basin edge and in deep-basin sites, respectively. While newer bridges perform considerably better in outside-basin sites, their performance is comparable to older bridges at basin-edge and deep-basin locations.Applied Science, Faculty ofCivil Engineering, Department ofGraduat