Zhou Shi

The complex mechanical behavior of a steel–concrete joint (SCJ) in a bidirectional curved pylon of a cable-stayed bridge is investigated using finite-element analysis (FEA) and a 1:4 scaled full-section model test. Formulas for the stress distribution and stress nonuniformity coefficients of the concrete in the SCJ are proposed to evaluate the force transmission characteristic of the SCJ. The FEA results indicate that variations in the section stiffness at both the bearing plate and the end of the steel structure result in abrupt stress changes and distinct spatial force characteristics of the SCJ. The experimental results reveal that the SCJ exhibits better force resistance than the concrete and steel transition segments, and the force transfer is dominant through the bearing plate. The proposed formulas are validated by using the measured results, which reveal significant nonuniformity in the stress distribution. The stiffness variation at the bearing plate, nonuniform concrete stress distribution, and spatial force characteristics should be considered during the design of similar SCJs in spatial pylons.

Purpose: This study aims to research the development trend, research status, research results and existing problems of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.Design/methodology/approach: Based on the investigation and analysis of the development history, structure form, structural parameters, stress characteristics, shear connector stress state, force transmission mechanism, and fatigue performance, aiming at the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge, the development trend, research status, research results and existing problems are expounded.Findings: The shear-compression composite joint has become the main form in practice, featuring shortened length and simplified structure. The length of composite joints between 1.5 and 3.0 m has no significant effect on the stress and force transmission laws of the main girder. The reasonable thickness of the bearing plate is 40–70 mm. The calculation theory and simplified calculation formula of the overall bearing capacity, the nonuniformity and distribution laws of the shear connector, the force transferring ratio of steel and concrete components, the fatigue failure mechanism and structural parameters effects are the focus of the research study.Originality/value: This study puts forward some suggestions and prospects for the structural design and theoretical research of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.

An innovative steel–concrete joint (SCJ) was applied to long-span railway hybrid box girder cable-stayed bridges to achieve favorable force transfer and deformation performance with a running train. The fatigue performance of each component was investigated by performing a full-scale 3 million cycle fatigue test. All components remained intact over the first 2 million cycles, indicating sufficient fatigue resistance over the designed service life. Turning points appeared in the curve for the shear stud on the first layer of the bottom plate and top plate after loaded 2.2 and 2.4 million loading cycles, respectively, resulting from the separation between the steel and concrete near end bearing plate, indicating that this area was the least favorable aspect of this innovative SCJ. Cracks then developed at the weld joint between the top plate and the end bearing plate after 2.4 million loading cycles, indicating that the fatigue life of the weakest weld joint exceeded 167.5 years. Numerical analysis with a nonlinear finite-element model was developed to further investigate the fatigue performance of the SCJ. The results indicated that the thickness of the end bearing plate and diameter of the shear studs significantly influenced the fatigue performance, and a 44–70-mm-thick end bearing plate and no less than 19-mm shear stud diameter is accordingly recommended. The outcomes of this study provide a reference for the further application of SCJ technology to long-span railway hybrid girder cable-stayed bridges.

The fatigue performance of a new type of butt-welded tensile-plate cable-girder anchorage that requires higher load-bearing capacity and lower stress concentration compared with normal tensile-plate anchorages for a long-span cable-stayed railway bridge was evaluated using a finite-element analysis and full-scale laboratory model. The test results show that the stresses remained constant over the first 2 million fatigue cycles, stress redistribution occurred at the end of the butt weld after 2.75 million cycles, and no surface cracks were observed after 3 million cycles. Anatomical milling tests found a fatigue crack originating from a microscopic welding defect in the end of the butt weld. The fatigue properties of butt welds of the anchor plate combined effect of tensile and shear forces are lower than the common butt welds. The fatigue details at two ends of the butt weld are crack vulnerable for the relative weak weldability of 40-mm-thick anchor plate. However, the measured minimum fatigue life of 2.75 million cycles (or 137.5 years) for the butt weld is larger than the bridge design requirement of 2 million cycles (or 100 years), indicating satisfied fatigue performance of the anchorage. The addition of leading and blowout plates is suggested to reduce butt weld residual stresses and defects, improving the fatigue performance of the anchorage.