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Shape optimization of a bowstring truss for transitional bridging

Transitional bridges – bridges that can be rapidly erected for immediate use and than transformed for a higher load capacity – can facilitate the restoration of vital transportation arteries following natural or anthropogenic hazards and, when transformed, support long-term recovery and reconstruction efforts. A strategy for implementing this approach is to utilize conventional portable bridge modules (i.e., Bailey Bridge system) in a standard girder-type layout for immediate relief. These modules can then later be re-used and re-configured into alternative bridge forms (i.e., bowstring truss) with higher load carrying capacity. A challenge in implementing this approach, however, is determining an efficient bowstring truss shape in which each member (i.e., vertical, diagonal, and lower chord) is comprised of fixed-length portable bridge modules. This research implements optimization to determine the shape of a uniformly loaded bowstring truss for minimum axial force in a member and minimum self-weight. Design variables include the number of modules per member. Constraints include geometric compatibility between members and a target span length. Since this multi-objective optimization problem includes nonlinear objective functions and discrete design variables, the heuristic algorithm Simulated Annealing is utilized. An optimized solution is found and is analyzed under American Association of State Highway and Transportation Officials (AASHTO) design loads. This solution is then compared against the performance of a standard girder-type layout.

This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1351272. The authors are grateful for the advice of Ted Zoli of HNTB Corporation on this research.

Author(s):

Evan Gerbo    
University of Notre Dame
United States

Casey Casias    
University of Notre Dame
United States

Ashley Thrall    
University of Notre Dame
United States