UBC Theses and Dissertations
Displacement demands for performance based design of skewed bridges with seat type abutments Catacoli, Seku Samory Mosquera
Skewed bridges are irregular structures due to the geometry of the deck and bents. Past earthquakes indicate that skewed bridges with seat type abutments exhibit greater damage than their non-skewed pairs. The damage has been attributed to in-plane rotations caused by pounding between the skewed deck and its abutments during strong ground shaking. This thesis combines experimental and analytical approaches to understanding the displacement demands on skewed bridges. As part of the experimental studies, results from ambient vibrations tests help to better understand the importance of directionality in the lateral response of skewed bridges. The predominant direction of the transverse response occurs in the direction of the skew bents; whereas the predominant direction of the longitudinal response is perpendicular to the skew. In addition, the analysis of records from an instrumented skewed bridge confirmed accelerations that could produce in-plane rotations of the deck. A comprehensive parametric study based on nonlinear dynamic analyses was performed to evaluate the effects of different skew angles, abutments types, and soil-foundation-structure interaction. The results demonstrated that elastic methods recommended by current seismic design provisions, and commonly used in standard practice, do not properly capture the in-plane rotations of the deck due to pounding. To overcome this shortcoming, a simple and effective method is proposed here to evaluate the displacement demands of skewed piers accounting for in-plane deck rotations. The proposed method uses validated simplified nonlinear models to generate torsional sensitivity charts for specific bridge prototypes. The charts provide peak in-plane deck rotation estimates as a function of bridge skew angle and the in-plane rotational period. An advantage of this approach is that it requires the designer to only conduct a linear dynamic analysis of the bridge. Nonlinear analysis required to assess the in-plane deck rotation is replaced here by torsional sensitivity charts. The proposed approach is able to predict the displacement response for a comprehensive range of skewed bridge prototypes by capturing the effects of the main parameters controlling the response. The information presented in this thesis will help improve the existing recommendations for performance based design of skewed bridges.
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