The high-strength bolt shear connector in prefabricated concrete slab has advantages in applications as it reduces time during the construction of steel-concrete composite building structures and bridges. In this research, an innovative and advanced bolt shear connector in steel-concrete composite structures is proposed. To investigate the fundamental mechanical behavior and the damage form, 22 static push-off tests were conducted with consideration of different bolt dimensions, the reserved hole constraint condition, and the dimension of slab holes. A finite element (FE) model was established and verified by using test results, and then the model was utilized to investigate the influence of concrete strength, bolt dimension, yield strength, bolt pretension, as well as length-to-diameter ratio of high strength bolts on the performances of shear connectors. On the basis of FE simulation and test results, new design formulas for the calculation of shear resistance behavior were proposed, and comparisons were made with current standards, including AISC, EN 1994-1-1, GB 50017-2017, and relevant references, to check the calculation efficiency. It is confirmed that the proposed equation is in better agreement with the experimental results.

High-strength bolted shear connectors (HSBSCs), which can be demounted easily and efficiently during deconstruction, are recommended to replace the conventional steel studs in steel–concrete composite beams (SCCBs) to meet the requirements of sustainable development. The existing investigations on the behavior of HSBSCs mainly focus on the positive moment area of composite beams, in which the concrete slab is in compress condition. In this paper, a three-dimensional finite element model (FEM) was developed to investigate the performance of HSBSCs subjected to inverse push-off loading. Material nonlinearities and the interactions among all components were included in the FEM. The accuracy and reliability of the proposed FEM were initially validated against the available push-off test results. Load-carrying capacity and load–slip response of the HSBSCs under inverse push-off loading were further studied by the verified FEM. A parametric study was carried out to determine the influence of the concrete strength, the diameter and tensile strength of bolt and the clearance between the concrete slab and the bolt as well as the bolt pretension on the shear performance of HSBSCs. Based on the extensive parametric analyses, design recommendations for estimating the shear load at the first slip and load-bearing resistance of HSBSCs were proposed and verified.

Train vibration from closely aligned adjacent tunnels could cause safety concerns, especially given the soaring size of the tunnel diameter. This paper established a two-dimensional discrete element model (DEM) of small (d = 6.2 m) and super-large (D = 15.2 m) diameter cross-river twin tunnels and discussed the dynamic characteristics of adjacent tunnels during the vibration of a train that runs through the tunnel at a speed of 120 km/h. Results in the D tunnel showed that the horizontal walls have the same horizontal displacement (D_H) and the vertical walls have the same vertical displacement (D_V). The stress state of the surroundings of the D tunnel is the decisive factor for D_H, and the distance from the vibration point to the measurement point is the decisive factor for D_V. Results in the comparison of the d and D tunnels showed that the D tunnel is more stable than the d tunnel with respect to two aspects: the time the tunnel reaches the equilibrium state and the vibration amplitude of the structure’s dynamic and static responses. The dynamic characteristic of the d and D tunnel is significantly different. This research is expected to guide the design and construction of large diameter twin tunnels.

Steel lightweight aggregate–concrete composite beams (SLACCBs) with bolted shear connections provide several advantages, such as reducing the overall self-weight, shortening the construction period, and improving the structural seismic performance. However, current research on the mechanical behavior of bolted connections is primarily concentrated on composite structures with normal concrete (NC), and there is no investigation focused on the shear performance of bolt connections embedded in lightweight aggregate concrete (LAC) slabs. Therefore, this paper developed a three-dimensional (3D) numerical model to study the shear properties of the bolt connections embedded in SLACCBs by utilizing ABAQUS software. Nonlinear geometric effects and material nonlinearities were considered in the finite element (FE) modelling. The accuracy and reliability of the FE modelling were initially calibrated and validated against the push-off tests described in the literature. Subsequently, the basic shear properties of the bolted connection embedded in SLACCBs were studied and compared with those of the bolted connection embedded in the NC slab by applying the verified FE modelling. Meanwhile, the effects of the concrete strength, concrete density, bolt diameter, and bolt tensile strength on the shear behavior of the bolt connections embedded in SLACCBs were also investigated using extensive parametric studies. Finally, some design formulae were proposed to predict the bolt connection shear strength.

Presently, the heat dissipation design of DC charger of electric vehicle mainly adopts forced air cooling, which has poor sand and dust-proof performance. This paper provides a kind of air inlet filter scheme with curved structure. The ventilation and protection performances of four kinds of filter screens were tested by high temperature heat dissipation test and dust-proof test, which is of great significance to the protective design of chargers with forced air-cooled heat dissipation. Nylon filter screen and non-woven fabric filter screen have the best heat dissipation effect. The sand proof effect of non-woven fabric filter screen is better than nylon filter screen. The scheme of combining the structure of curved air inlet and non-woven fabric filter screen is the optimal scheme which has important application significance and popularization value.