Optimization method for the length of the outsourcing concrete working plane on the main arch rib of a rigid-frame arch bridge based on the NSGA-II algorithm

In addressing the challenges of determining the length of the outsourcing concrete working planes on the main arch rib of rigid-frame arch bridges—a process often reliant on extensive engineering experience, large-scale manual calculations and lack of multi-objective control. This paper employs the NSGA-II multi-objective optimization algorithm, where the objective functions are set to minimize the maximum compressive stress, tensile stress, and vertical deformation of the arch crown after the bridge was built. Optimization studies of the outsourcing concrete working plane length were conducted in different pouring schemes. Based on the case study of a main arch rib specimen with a span of 60 m, the optimal results for different construction schemes were derived. The uneven stress distribution coefficient of key sections was used as the evaluation index to filter the Pareto-optimized solutions from the NSGA-II optimization results. The experimental results indicated that: (1) Compared with the original pouring scheme, the optimized scheme respectively reduced the structure's maximum compressive stress, tensile stress, and vertical deformation of the arch crown by 4.19 MPa, 0.12 MPa, and 1.74 mm, showing a decline of 24.19%, 19.67%, and 2.82%. (2) Seven distinct outsourcing concrete pouring schemes were devised by altering the number of working planes, segments per working plane, and concrete pouring direction. All schemes achieved favorable optimization results through length optimization, demonstrating the broad applicability of the NSGA-II algorithm. (3) The stress distribution coefficients non-uniformity for the outsourcing concrete of the main arch rib are mostly located in the range of [0.7, 0.8], surpassing the original scheme's 0.69. Therefore, the NSGA-II algorithm not only ameliorates the primary arch rib's stress condition and diminishes the arch crown's vertical deformation, but also elevates the post-construction stress distribution state of the bridge's outsourcing concrete.