The perforated rib shear [Perfobond Leiste in German (PBL)] connector is a type of shear connector used in some steel–concrete composite bridges as a main load-transfer element between the concrete roadway and the supporting steel deck. The shear capacity of PBL connectors is affected by several connection parameters, such as the diameter of the transverse steel reinforcement, the size of the perforated rib hole, and the thickness of the rib plate, and the stress state in the surrounding concrete. In the present study, 33 test specimens were designed, and push-out tests were performed to investigate how these parameters affect the shear capacity of PBL connectors. The test results show that the shear capacity of these connectors increased with an increase in the diameter of the transverse reinforcing bar, an increase in the size of the rib holes, and an increase in thickness of the perforated rib plate. As for the effect of concrete stress state, it was found that the shear capacity of the connectors increased when a transverse compressive stress was present, but it decreased when a transverse tensile stress was present. Using results from these tests, a design equation that takes all of these factors into consideration in determining the shear capacity of PBL connectors is proposed. The proposed equation produces reasonably accurate results when compared with experimentally determined shear capacity for these connectors.

In this paper, a two-dimensional (2D) model for wave-current girder interactions is established to investigate the effect of wave-current forces on box girder bridges. Reynolds averaged Navier-Stokes (RANS) equations combined with the k-ε turbulence model are applied for wave-current simulations, and the volume of fluid (VOF) method is used to trace the free water surface. Compared with previous studies, this paper (1) investigates the influence of the current velocity on the wave force on a coastal bridge box girder under extreme conditions, (2) analyzes the wave forces on the vulnerable positions of a box girder bridge, and (3) proposes simple and accurate equations for predicting the wave-current forces on a box girder bridge. The numerical model presented in this paper is first validated by comparing data obtained from the laboratory experiments. Next, parametric studies are conducted to examine the influence of the current velocity on wave-current forces under different effect factors, including extreme wave characteristics, relative water depths, and submerged depths. The influence of the geometrical shape of the box girder on the wave forces is considered. Finally, based on the numerical results, empirical equations predicting the wave-current forces on a box girder bridge under various effect factors are proposed as a method of protecting coastal bridges from damage under extreme wave loadings.

To study the bond performance between shotcrete and rock in a hot and humid tunnel, experiments on wet-sprayed shotcrete specimens under different hot and humid curing conditions (35°C, 50°C, 70°C, and standard curing conditions: 20°C with relative humidity 95%) were performed to examine the influence of thermal damage. The results show that the bond strength at 35°C is higher compared with that at standard curing conditions, but decreases when the temperature rises (especially at 70°C), indicating the adverse effects of thermal damage on bond strength. Based on these results, we used the worst hot and humid condition (70°C) as a case study to explore measures to improve bond strength under hot and humid conditions by adding mineral admixture or fiber material to the shotcrete mix. The experimental results suggest that adding fly ash or slag powder can enhance the bond strength, with the best effect achieved by adding fly ash.

To solve the problem on the serious loss of bond strength of shotcrete in hot and dry environments, the measures for improving the bond strength were explored by mixing mineral admixtures or fiber materials into shotcrete mixture. The bond strengths between shotcrete and rock in hot and dry environments were measured by splitting method, and macroscopic, mesoscopic and microscopic analyses were carried out on shotcrete specimens. The results show that: in hot and dry environments, the bond strengths all decrease when mixed with mineral admixtures, and especially for the fly ash, with which the bond strength of shotcrete decreases by 36.7%. Mixing polypropylene fibers into shotcrete makes its bond strength decrease by 10.2%, but for steel fibers, it will be improved by 41.8% compared with basic mix proportion. Moreover, according to submicroscopic measurement and microscopic analysis, the influence mechanisms of mineral admixtures and fiber materials have been explored to some extent. Therefore, it’s feasible and effective to improve the bond strength by adding steel fibers in hot and dry environment.