Progressive collapse prevention design of fly-bird-type arch bridges considering tie bar failure

To enhance the progressive collapse prevention ability of the fly-bird-type arch bridges in the event of tie bar failure, four locally strengthened structural systems were proposed based on the alternative path method of robust design along with relevant engineering cases and studies: triangular stiffener zone system, concrete-filled steel tube column system, columns with diagonal compression bars system, and partially simply-supported column connection system. An explicit dynamic cable-breaking simulation method was established using LS-DYNA. Based on laboratory test data and simulation results, the method was compared and validated. The dynamic response of four structural systems under tie bar failure was simulated using this cable-breaking simulation method. The ultimate internal force indices of main-span and side-span members were compared, and the structural bearing capacity of each system under tie bar failure conditions was evaluated. According to the results, with smaller error, the LS-DYNA dynamic analysis is suitable for simulating the dynamic response of horizontal tie bar failure of the tied-arch bridge. All four structural systems effectively reduce the dynamic response of the rest structures under tie bar failure. Specifically, the concrete-filled steel tube column system is most advantageous for reducing the dynamic response of the bending moment of the side arch rib and longitudinal beam, while the partially simply-supported column connection system is most effective in minimizing the dynamic response of bending moment of the main arch rib and column. The application of concrete-filled steel tube column systems in the construction of new fly-bird-type arch bridges provides the best overall benefits in terms of structural dynamic performance and aesthetic coordination. Meanwhile, the application of partially simply-supported column joints in the reinforcement of existing fly-bird-type arch bridges not only enhances structural dynamic performance but also effectively prevents joint cracking. Additionally, this approach maintains a low construction cost with simplicity and practicality, achieving the optimal economic efficiency. Therefore, practical and viable approaches are provided for the robust design and reinforcement of this type of bridge.