The early cracking of concrete beam bridges remains a concern in civil engineering. An analytical model considering the combined effect of thermo-hydro-mechanical processes forms the basis for assessing the cracking risk of girders during construction. Based on the equivalent hydration theory, the temperature and moisture conduction processes and the evolution of the mechanical properties of concrete were modeled as a function of the equivalent age. A coupling model for the temperature and moisture fields was established, and a theoretical framework for analyzing the thermo-hydro-mechanical combined effect was presented. Based on this, a numerical analysis method was proposed and implemented into ABAQUS; the results were validated with some typical tests. Finally, a long-span prestressed concrete (PC) box girder bridge with balanced cantilever construction was taken as an example, and the causes of web cracking and its impact degree were analyzed. The results show that the rate of moisture conduction is significantly lower than the rate of temperature conduction; even for thin-walled components, there exists a significant humidity gradient on the surface layer. The humidity-induced shrinkage and restraint of the precast members are the main causes of web cracking.

To analyze the time-varying temperature field distribution pattern of ballastless track steel-concrete composite box girders for a high-speed railway at ambient temperature, a numerical model for analyzing the time-varying temperature field of steel-concrete composite box girders was established based on the long-term monitoring data for the internal and external environments of the main girder of the Ganjiang Bridge on the Nanchang-Ganzhou high-speed railway. The influence of factors such as the deck pavement and the ambient wind speed on the time-varying temperature field of the steel-concrete composite box girders were considered. The results showed that there was a significant difference in the vertical temperature gradient patterns on sections at the side web and at the middle web at the same moment in time due to the hindering effect of the track board on the heat exchange between the ambient temperature and the main girder. Increasing the wind speed accelerated the rate of heat exchange between the main girder surface and the environment. In particular, when the internal temperature of the girder was higher than the ambient temperature, the higher the wind speed was, the larger the temperature gradient was. This study lays a foundation for accurate analysis of the structural response of ballastless track steel-concrete composite girder bridges at ambient temperature.

Due to its excellent mechanical performances, axially loaded concrete-filled steel circular tube (CFST) columns have been widely used in structural engineering. As an important long-term behaviour of CFST structures, the creep has an obvious nonlinear property under high stress levels, which makes the influence of creep more complicated. In this study, to analyze the impacts of nonlinear creep effect on the behaviour of axially loaded short CFST columns, a complete theoretical framework for coupling analysis of 3D creep effect and material nonlinearity was presented. First, the concrete damaged plasticity model with a uniform constraint (UCCDP) was established to simulate the plasticity and damage evolution of a concrete core. Next, based on the UCCDP, a method of 3D nonlinear creep analysis and a corresponding numerical analysis method were established and implemented in the ABAQUS secondary platform. Finally, by comparing the predicted results with the experimental results, it was observed that the method proposed to predict the creep of axially loaded short CFST columns had satisfactory accuracy.

Substructuring approaches possess many superiorities over traditional global approaches in damage identification because large-size global structures are replaced by small and manageable substructures. This paper proposes a substructural time series model for locating and quantifying the damage in complex systems. A substructural autoregressive moving average with exogenous inputs (ARMAX) model is established to extract the frequencies and mode shapes of substructures as indicators for damage detection. The detection of structural damage is essentially an inverse problem, and the damage in structure bears sparse properties. The inverse problem of substructural damage identification is efficiently solved via sparse regularization, and structural damage can be located and quantified through the nonzero terms in the solution vector. The accuracy of the proposed method is demonstrated by the numerical simulation of a frame structure and shaking table test of a shear building structure. As the substructural properties are more sensitive to local structural damage than the global properties, the substructural ARMAX model is quite accurate and efficient to be used in the damage identification of a complex system.

<p>Quanzhou Bay Railway Bridge is the key component of the Fuzhou-Xiamen High-Speed Railway with the design speed of 350 km/h. The total length of 20.3 km is the greatest among the sea- crossing high-speed railway bridges in the world. The main structure over the main navigation channel is a steel-concrete composite cable-stayed bridge with the span arrangement of（ 70+130+400+130+70）m. The main girder adopts a closed and streamlined box section.</p><p>In the past decades, the sea-crossing railway cable-stayed bridges mostly adopted steel truss girder. Quanzhou Bay Railway Bridge is the first railway bridge adopting the steel-concrete composite box girder cable-stayed bridge type in china and the longest-span sea-crossing high- speed railway bridge in the world. In this paper, the structural design and construction method for this bridge are presented.</p>