Yang Zhou

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.