UBC Theses and Dissertations
Seismic fragility assessment in the transverse direction of a steel bridge bent considering soil-structure Interaction Judd, Trevor James Richard
This research developed the analytical seismic fragility of a two-pier hollow cross-sectional steel highway bridge bent prevalent in British Columbia (B.C.). Nonlinear incremental dynamic time history analysis results obtained from SeismoStruct models subjected to ground motion records were used to develop the fragility curves. They represent the probability of exceeding a performance or damage limit state at a specific ground motion intensity. Peak ground accelerations between 0.047g and 2.654g, from a compliment of 12 synthetic ground motion records and 16 scaling steps, were used in the nonlinear incremental dynamic time history models (IDTHM). Seven primary factors were considered to produce 2⁷ different 3D finite element models of steel bridge bent combinations having equivalent soil-structure interaction considering shallow spread footing on soil type III as per Canadian Highway Bridge Design Code CAN/CSA-S6 (CHBDC). Fractional factorial design (FFD) was employed for parametric study, which additionally reduced computing time. Bridge bent factors of height, wall thickness and corrosion were determined to be the most influential primary factors. The FFD predictive models for each damage limit state (LS) were plotted, with a close correlation between the predictive models and the initial bridge for three out of four damage LS at a PGA of 0.24g and 0.76g with a maximum difference of 13% in all models. Fragility curves employing characteristics of CHBDC soil types II, III and IV for moderate to soft soils were developed for specific evaluation of the bridge bent construction style, establishing the influence of soil conditions on the seismic vulnerability of bridge bent designs. Comparison of soil type fragility curves concluded softer soils generally equate to higher probabilities of exceeding a damage LS, with a variation for a smaller cross-sectional bridge bent at moderate and extensive damage limit states. Slight and moderate damage LSs were influenced more at low PGAs of 0.24g and extensive and complete damage LSs at high PGAs of 0.76g.
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