Automated design optimization of bowstring tied-arch concrete bridges

This article presents an optimization-based approach to assist in the design of bowstring tied-arch concrete bridges. This approach comprises an automated procedure to define initial designs and a gradient-based algorithm, from which local optimum solutions are obtained, and the least-cost solution is selected as the optimum design. The finite element method is used for the three-dimensional analysis considering several load cases, geometrical nonlinearities and time-dependent effects. The design is posed as a cost minimization subject to constraints on the displacements and stresses defined according to the Eurocodes provisions. A constraint aggregation approach is adopted to solve the problem by minimizing a convex scalar function. The discrete direct method for sensitivity analysis provides the algorithm with the structural response to changes in the design variables. The design variables are the arch and deck cross-sectional sizes, the hangers and tendons cross-sectional areas and prestressing forces, the geometry of the arch, the hangers’ layout and the number of hangers’ anchoring points in the deck. The optimization of a 120 m single-span bridge illustrates the features and applicability of the proposed approach. Optimum solution with Nielsen layout, deck slenderness of 1/150 and arch rise-to-span ratio of 1/5.