Large-diameter concrete-filled steel tube (CFST) members are being increasingly utilised owing to their ability to carry larger loads and resist bending. Upon incorporating ultra-high-performance concrete (UHPC) into steel tubes, the resulting composite structures are lighter in weight and much stronger than conventional CFSTs. The interfacial bond between the steel tube and UHPC is crucial for the two materials to effectively work together. This study aimed to investigate the bond-slip performance of large-diameter UHPC steel tube columns and the effect of internally welded steel bars in steel tubes on the interfacial bond-slip performance between the steel tubes and UHPC. Five large-diameter UHPC-filled steel tube columns (UHPC-FSTCs) were fabricated. The interiors of the steel tubes were welded to steel rings, spiral bars, and other structures and filled with UHPC. The effects of different construction measures on the interfacial bond-slip performance of UHPC-FSTCs were analysed through push-out tests, and a method for calculating the ultimate shear bearing capacities of the interfaces between steel tubes containing welded steel bars and UHPC was proposed. The force damage to UHPC-FSTCs was simulated by establishing a finite element model using ABAQUS. The results indicate that the use of welded steel bars in steel tubes can considerably improve the bond strength and energy dissipation capacity of the UHPC–FSTC interface. R2 exhibited the most effective constructional measures, resulting in a significant increase in ultimate shear bearing capacity by a factor of approximately 50 and energy dissipation capacity by a factor of approximately 30 compared to R0 without any constructional measures. The load-slip curve and ultimate bond strength obtained from finite element analysis and the interface ultimate shear bearing capacities of the UHPC-FSTCs obtained using the calculation method agreed well with the test results. Our results provide a reference for future research on the mechanical properties of UHPC-FSTCs and their engineering applications.

In cold regions, freeze-thaw (F-T) damage is the main detriment to the durability of reinforced concrete structures, which will reduce the bond performance between concrete and rebar, and then adversely affect the bearing capacity and stiffness of structures. In this study, 21 groups of tests were performed to analyze the effects of the number of F-T cycles, volume stirrup ratio, and replacement percentage of recycled aggregate on the bond performance between recycled aggregate concrete and deformed rebar. The stirrup stress during the pulling process was measured using strain gauges attached to the stirrup surface, and the contribution of the stirrup to the bond strength was analyzed. The results showed that the F-T damage and stirrup constraints could affect the failure mode, the bond strength and the peak slip of pullout specimen. The failure mode of specimen with stirrups could be determined by splitting angle index. The indirect contribution of stirrup accounts for 14–25% of the bond strength and increases with the increase in F-T damage. The full bond-slip curve was obtained by fitting four parameters including splitting tensile strength, constraint coefficient, splitting angle index and brittleness index.

According to current regulations, welding is strictly prohibited for prestressed and tension cables. In response, this article proposes the use of a portable spot-welding machine to spot weld steel strands. This method generates a small current during spot welding, with a voltage of only 3 V to 5 V, and does not damage the internal structure of the steel strand. To effectively monitor cable tension in cable-supported structures, a novel approach utilizing a chip-based, encapsulated spot-welded strain sensor was investigated. The strain sensing capability, temperature sensitivity, stress relaxation, and static load responses were investigated on the proposed smart steel strand cables with spot-welded strain sensors. The theoretical analyses and finite element simulations revealed that the strain transfer efficiency of the spot-welded strain sensor exceeded 96%. The experimental results demonstrated that the load-strain relationship of the smart steel strand cable had a fitting degree greater than 0.999, and the tension errors obtained under different loads were within 1.26%. The tension full capacity errors measured at different temperatures were generally within 1.0%. The relaxation rate of the smart steel strand cable after 120 h was 3.78% and reduced the sensor accuracy error by 3.97%. Thus, the proposed strain sensor equipped with a smart steel strand cable is suitable for use in long-term tension monitoring.

As an important component connecting the upper and lower structures of a bridge, bridge bearings can reliably transfer vertical and horizontal loads to a foundation. Bearing capacity needs to be monitored during construction and maintenance. To create an intelligent pot bearing, a portable small spot welding machine is used to weld pipe-type welding strain gauges to the pot bearing to measure strain and force values. The research contents of this paper include the finite element analysis of a basin bearing, optimal arrangement of welding strain gauges, calibration testing, and temperature compensation testing of the intelligent basin bearing of the welding strain gauges. Polynomial fitting is used for the fitting and analysis of test data. The results indicate that the developed intelligent pot bearing has a high-precision force measurement function and that after temperature compensation, the measurement error is within 1.8%. The intelligent pot bearing has a low production cost, and the pipe-type welding strain gauges can be conveniently replaced. The novelty is that the bearing adopts a robust pipe-type welding strain gauge and that automatic temperature compensation is used. Therefore, the research results have excellent engineering application value.

Most cable arch bridge damage accidents are caused by bridge collapse due to fracture of the short sling of the arch bridge. The service life of the short sling is much lower than the design life, mainly resulting from the action of vehicles and temperature, and the arch rib and the bridge floor will have relative displacement along the bridge direction, which leads to the emergence of bending stress due to the different axes at both ends of the short sling, forming local stress concentration. The stress concentration is coupled with corrosion to accelerate the damage to the sling. To study the influence of shaft deflection on the mechanical properties of short slings of steel strands in arch bridges, this study analyzes the distribution law of the shaft deflection angle of arch bridge slings under the action of vehicle and temperature loads for a medium-bearing arch bridge with a main span of 560 m. The results show that under different vehicle and temperature loads, the axial deflection angle of the short sling is the largest, and the closer it is to the center of the span, the smaller the axial deflection angle. The static and fatigue properties of 1, 3, 7, 9, 12, 19, and 27 strands of whole bunch extruded strand slings were simulated and analyzed under a $0.45{\sigma }_b$ force when the axial deflection angle of the strand slings was 0 mrad, 10 mrad, 20 mrad, and 30 mrad. The results show that the ultimate tensile properties, breaking strength, and fatigue life of the strand slings decreased to a certain extent with increasing shaft deflection angle. The accuracy of the finite element models is verified by the ultimate tensile test and the fatigue test. This study explores the bending deflection results of the short slings of arch bridges due to the different axes of the upper and lower anchorages and provides the necessary theoretical support for the design and fatigue life estimation of the short slings of arch bridges.