Fatigue Performance of a Novel Steel-Concrete Joint of a Long-Span High-Speed Railway Hybrid Girder-Cable-Stayed Bridge

The steel-concrete joint (SCJ) of a railway hybrid girder-cable-stayed bridge transmits tremendous internal forces, resulting in complex structure and stress. The existing complex SCJs lead to difficulties in on-site concrete construction, and the complex stress of the SCJ under train load is prone to diseases such as steel concrete fatigue detachment and cracking. To investigate the complex fatigue performance of a novel SCJ for a long-span high-speed railway hybrid box girder-cable-stayed bridge with a main span of 672 m, finite-element analysis (FEA) and a 1:2 scaled fatigue model test with 2.15 million cycles were conducted. The results showed that the numerical fatigue stresses of the SCJ exhibited a significant shear lag effect in the transverse direction with unfavorable fatigue stresses at the side box. After 1.70 million loading cycles, all the steel plates of the test model remained intact, indicating good fatigue resistance during the design life. Cracks appeared at the junction between the horizontal diaphragm and the web of the steel transition segment (STS) after 1.85 million cycles, showing a fatigue life of 118 years. The measured fatigue crack life of the concrete deck over the postanchor position of the prestressed tendons in the STS was 30.5 years for the local concentrated tensile stress, which can be improved by casting the concrete after the tendons are prestressed. No fracture or other abnormalities occurred in the shear studs and perforated rib (PBL) rebars, and the deflection of the test model and the slip between the steel and concrete were insignificant during the fatigue tests, indicating the good fatigue performance of the SCJ, which was better than that of the STS. The thickness of the bearing plate and diameter of the shear studs for the actual SCJ were suggested to be 40-60 and 16-25 mm, respectively, based on a parametric study.