It is necessary to pay attention to the bonding strength of the interface between precast normal strength concrete (NSC) and cast-in-place epoxy resin concrete (EMR) when using EMR as a repair or filling material or an overlay in bridges’ rehabilitation. However, the performances of epoxy concrete are different due to differential mix ratios; thus, the bonding properties between various epoxy resin concrete and cement concrete are not completely the same. This article investigated the interfacial bond properties between NSC and ERC by direct tensile, push-out, and slant shear test with specimens of special size and structure and observed the interfacial bond strength and corresponding failure modes. The minimum bond strength under direct tension was 0.72 MPa, while the minimum bond strength was 1.71 MPa and 3.19 MPa for the push-out test and slant shear test, respectively. Results indicated that the slant shear test specimens with an inclination angle of 45° are not suitable for the slant shear test due to higher compressive stress. Furthermore, the cohesion and friction coefficient of interface bond strength were calculated inversely in accordance with the results obtained from the corresponding direct tensile and slant shear tests. The minimum cohesion value was 1.71 MPa, and the minimum friction coefficient value was 0.46.

At present, there are few studies on the thermal effect of solar radiation on a separated double-sided box steel-concrete composite girder cable-stayed bridge. In this paper, the beam element and mixed element models are combined with the theory of transient heat transfer analysis and meteorology; this approach is adopted to carry out a thermodynamic analysis of a related bridge project. The calculation results of the thermal field and structural thermodynamic analysis of bridge sections show that, in terms of a separated double-sided box steel-concrete composite girder cable-stayed bridge, the thermal field distributions of the main girder and the pylons are extremely complex under conditions of solar radiation. Therefore, the real thermal field cannot be accurately described as a one-dimensional temperature gradient. The traditional beam element model cannot accurately simulate the temperature effect, and it will underestimate its thermal effect. The calculated temperature stress values of the mixed element model are quite different from those of the of beam element model. The mixed element model can precisely reflect the local thermal effect of each component in this system under solar radiation. Compared with the calculation results of the beam element model, the maximum temperature stress of the bridge deck in each section of the main girder is generally 20% larger; the maximum temperature stress levels of the steel-beam top and bottom plates are 14.7 MPa and 15.9 MPa larger, respectively. The maximum shear stress of the steel-concrete interface is 0.2 MPa larger. The research results of the temperature effect calculated by the mixed element have an important guiding significance for the design and maintenance of bridges.

Modern cable-stayed bridges are spatial, multicable systems. The cable force needs to be adjusted during the construction phase and maintenance phase. The existing calculation methods of cable force adjustment mainly considered the rationality of structural force, but only few research studies have been conducted on how to reduce the number of stay cables which need to be adjusted. This study aims to propose an optimization calculation method including the optimization module with the sensitivity analysis and updating design variable module (UDVM), which are used for cable force adjustment in cable-stayed bridges. Based on the finite difference method, the sensitivity analysis is adopted in the optimization module, which can capture the response of structures as design variables vary; the particle swarm optimization method is adopted for structural optimization. The proposed method can dramatically reduce the number of stay cables which need to be adjusted and ensure the main girder stresses remain in a reasonable state during stay cable adjustment progress by UDVM. Moreover, the proposed method can continuously update the objective function, constraint conditions, and design variables. Finally, this proposed optimization calculation method is applied to two different cable-stayed bridges to validate the reliability and feasibility of the method.

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