Characteristics of sudden cable fracture and train-bridge coupled vibration of highway-railway cable-stayed bridge

To investigate the impact of sudden cable fracture accidents on the safety of bridge structures and running trains under operational conditions for highway-railway cable-stayed bridges, a train-bridge coupled vibration calculation program based on the explicit nonlinear finite element dynamic algorithm was developed. A three-dimensional full-bridge finite element model of an actual long-span highway-railway cable-stayed bridge was constructed. The completed bridge state under dead load was calculated by using the static nonlinear finite element method. By using the explicit nonlinear finite element method, the dynamic response of the bridge structure under continuous fractures of multiple stay cables was calculated. The positions of the fractured stay cables after falling and colliding with the main girder were calculated and analyzed. Furthermore, the dynamic responses of the bridge and train under a sudden cable fracture were calculated under different train-bridge coupled vibration conditions. The results indicate that the explicit finite element method can simply and intuitively simulate the cable fracture damage of cable-stayed bridges, possesses advantages in both accuracy and efficiency in the calculation of train-bridge coupled vibration, and has better technical applicability. The cable-stayed bridge structure has a high safety redundancy, and the remaining cables can effectively share the load after a cable fracture. The main girder may collapse only in an extreme case where more than 10 continuous stay cables fracture on one side. Under the action of a transverse wind with a speed of 30 m·s^-1, the fractured stay cable is prone to fall onto the upper deck of the main girder. After the fracture of a single stay cable, trains can maintain passage. At the moment of fracture of the longest stay cable 34# at the mid-span, the vertical and transverse displacements of the main girder change abruptly and significantly, and the vertical acceleration of the main girder jumps to approximately 20 m·s^-2. When a train travels on the bridge at a speed of 200 km·h^-1, and the longest stay cable 34# on the right side of the mid-span suddenly fractures, under extreme conditions, the maximum wheel load reduction rate reaches approximately 0.91, and the maximum derailment coefficient reaches approximately 2.73 within a short period of time. The main girder vibration caused by the cable fracture exposes the train to an obvious derailment risk. The research results can provide a reference for the safety assessment of cable-stayed bridges when cable fracture accidents occur.