Maximal deflection and deck-end rotation angle assessment for two-tower three-span suspension bridges under live load: An analytical algorithm

Two-tower three-span suspension bridges (2T3S-SBs) have found extensive applications worldwide due to their excellent spanning capacity and mechanical performance. With the continuous improvement of suspension bridge spans and the gradual emergence of high-speed railway suspension bridges, it is urgent to estimate the maximum deflection and maximum deck-end rotation angle of the stiffening girder under live load. For this purpose, this paper derives the deflection equations of the entire deck and deck-end rotation angle in a 2T3S-SB based on the deflection theory. The position and length of the live load are treated as design variables, and the deck deflection and deck-end rotation angle as objective functions. The maximum deck deflection under live load, maximum positive and negative deck-end rotation angles, and the corresponding live load conditions are estimated using the simulated annealing algorithm. The accuracy of the proposed analytical algorithm is validated by trial calculation using the finite element model (FEM). The analytical algorithm proposed in this article allows one to avoid the finite element modeling, influence line extraction, trial calculation for multiple load cases, or multi-point comparison. While ensuring calculation accuracy, it greatly improves the solving efficiency. In addition, the analytical algorithm is used to analyze the influence pattern of several structural parameters of the suspension bridge on the maximum deck deflection and maximum deck-end rotation angle: dead load, span length, ratio of side span to middle span, sag-to-span ratio in the main span, bending stiffness of the deck, axial stiffness of the main cable, and lateral stiffness of the tower.