Abstract
Skew bridges with seat-type abutments are frequently unseated in earthquakes due to large transverse displacements at their acute corners. It is believed these large displacements are due to in-plane rotation of the superstructure. Lack of detailed guidelines for modeling of skew bridges, many current design codes give empirical expressions rather than theoretical solutions for the additional support length required in skew bridges to prevent unseating. In this paper, a parametric study has been carried out to study the influence of skew angle, aspect ratio and fundamental periods of bridges on the additional support length requirements of single-span bridges due to skew using a shake table experiment validated Simplified Method, which is capable of simulating gap closure based on response spectrum analysis. This method is developed based on the premise that the obtuse corner of the superstructure engages the adjacent back wall during lateral loading and rotates about this corner until the loading reverses direction. A design response spectrum specified in AASHTO LRFD Specifications was employed to represent the design-level earthquakes. The results show the additional length required to prevent unseating due to skew increases with the skew angle in an approximately linear manner when the angle is less than a critical value and decreases for angles above this value. This critical skew angle increases with the aspect ratio approximately in a linear manner and shows negligible dependence on the fundamental periods of the bridges, and combination of span length and width. In addition, the critical skew angle varies between 58° and 66°, when the aspect ratio is varied from 3.0 to 5.0. The results also show that the empirical formulas for minimum support length requirements of skew bridges in current codes and specifications can not accurately reflect the influence of skew.
Highlights
Due to geometric and space constraints, skew bridges are commonly used as overpasses in highway interchanges or intersections, especially in urban areas
3 Conclusions In this paper, a comprehensive parameter study was carried out using a shake table experiment validated Simplified Method to investigate the influence of skew angles, superstructure aspect ratio, fundamental periods of the bridges and combinations of the span length and width on the additional support length requirements of bridges due to skew
This method is developed to estimate the additional support length requirements of bridges due to skew based on the premise that the obtuse corner of the superstructure engages the back wall of the abutment during lateral loading and the superstructure rotates about this corner
Summary
Due to geometric and space constraints, skew bridges are commonly used as overpasses in highway interchanges or intersections, especially in urban areas. With the advancement in the numerical modeling, accurate prediction of the seismic response of skew bridges may be achievable through 3-D dynamic analysis on rigorous finite element models (Wu and Buckle 2020). Wu et al (2019a) developed a simplified method to estimate the additional support length demands of bridges due to skew based on the unseating mechanism developed based on a shake table experiment, which is able to consider the bridge-abutment interaction. 2.2 Case 2 When the skew angle is medium or large, under the transverse earthquake action, the superstructure will move transversely to close the gap and rotate around one of the obtuse corners The N(θ) (see Fig. 2) is computed based on the following procedures
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