Shili Yang

Before 2014, cable-stayed bridges with steel box girders were rarely used in railways worldwide as their stiffness was deemed insufficient for train operation. Hence, hybrid box girder technology was introduced to railway cable-stayed bridges, making hybrid box girder cable-stayed bridges (HBGCBs) one of the most widely adopted railway cable-stayed bridge types in China. The introduction of HBGCBs has eliminated the heavy reliance on steel truss and prestressed concrete girders in railway cable-stayed bridges worldwide, especially in China. This review aims to illustrate how the rapid development of railway HBGCBs in China over the past decade was achieved through innovative stiffness enhancement technologies and key design considerations. This article first provides a valuable review of the development of railway HBGCBs and the factors that limited their international adoption prior to 2014. It then comprehensively highlights key stiffness control criteria and presents innovative stiffness enhancement strategies tailored to railway HBGCBs. It reveals that key design parameters, including the side-span–mid-span ratio, the position and form of the steel–concrete joint (SCJ), girder height, auxiliary pier configuration and pylon layout, are also important for the mechanical performance of railway HBGCBs. Typical construction methods for railway HBGCBs are also described. Finally, the article introduces a series of long-span bridge types derived from SCJ and girder technologies and discusses the feasibility of further span extension using the above technologies. The research results are conducive to the transformation of bridge design concepts and promote the further development and application of railway HBGCBs and related innovative technologies worldwide.

As China’s urban underground area grows, deep foundation pit projects in complex geological circumstances, particularly near critical infrastructure, must adhere to tight deformation control guidelines. However, limited research has been conducted on the deformation behavior of internal bracing systems in Sichuan’s sandy cobble strata. This research centers on a deep excavation near civil defense facilities in Pujiang County, Chengdu. We investigated the deformation characteristics of retaining piles and internal bracing systems using field monitoring, finite element simulations, and parameter sensitivity analysis, and proposed optimization solutions for the support scheme. Road settlement, pile-head vertical displacement, building settlement, and deep lateral displacement of retaining piles were all monitored in the field at different phases of excavation. MIDAS/GTS was used to generate a 3D finite element model that included bored piles as a contiguous pile wall. The model was verified against monitored data and showed a maximum variation of 3.7%. Parametric studies were conducted to optimize the equivalent stiffness of the contiguous pile wall and the standardized internal bracing system. The findings indicate that the maximum lateral displacement of retaining piles is the primary optimization restriction. Reducing the equivalent stiffness to 0.6t (relative to the baseline thickness t) causes displacement to surpass the warning threshold (35 mm), whereas increasing it to 1.2t or 1.4t limits deformation without incurring significant costs. Case G of the standardized internal bracing system ensures that the maximum pile displacement (21.95 mm) remains below the warning criterion (24.5 mm) while improving constructability. This work elucidates the deformation characteristics of internal bracing systems in sandy cobble strata near sensitive buildings, offering theoretical and practical assistance for comparable projects.

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.

This study conducted preliminary finite-element analysis (FEA) of an orthotropic steel deck (OSD) with U-ribs and V-ribs for a long-span cable-stayed steel-box girder railway bridge using the hot-spot stress method to determine the behavior of the welded connections. The results of the FEA indicated that V-ribs exhibited better fatigue performance than U-ribs on four typical fatigue details, and the rib-to-diaphragm welded connections in the two rib types were the most unfavorable aspects. A full-scale 5.6 million cycle fatigue test was then conducted to determine and compare rib fatigue resistance. The rib-to-diaphragm joints in the U-ribs were more prone to fatigue cracks than those in the V-ribs, and crack formation and extension did not result in significant deterioration of rigidity. The fatigue life of the U-ribs was 62.5 years, whereas that of the V-ribs was in excess of 169 years. The results indicated that the FAT90 (a stress range of 90 MPa at 2 × 10⁷ cycles) fatigue class was the most suitable for estimating the fatigue resistance of rib-to-diaphragm welded connections in a railway OSD.