To study the effect of the temperature field and gradient of a steel‐concrete composite box girder bridge, a 5 × 35 continuous composite box girder bridge is used as the research object. The temperature measuring point is set by selecting a typical cross section, and the temperature change data are measured. The temperature field of the different positions in the composite box girder bridge is studied, the global and local temperature differences are compared, and the law of temperature distribution and the main factors affecting the temperature field are formulated. The most unfavourable expression function of the vertical temperature gradient of the section is simulated using the measured data, the existing standard temperature gradient mode is compared, the finite element model of the bridge is established, and the influence of the actual temperature gradient mode on the stress and deformation of the composite girder is further analysed. The conclusions show that the temperature differences of different azimuth sections and the local temperature differences between the steel and concrete joint parts of the steel‐concrete composite box girder bridge are not significant. The temperature gradient heating and cooling model fitted by the measured temperature field can be used as a reference for the structural design of similar local bridges.

Seawater splashing and frequent rainfall in the coastal area will often cause the concrete members to be affected by dry-wet cycles. In order to investigate the effect of salt solution on the mechanical behaviours of geopolymer concrete under dry-wet cycles, a series of tests on erosion of geopolymer concrete by three different salt solutions were carried out by using the mass loss rate, compressive strength, erosion resistance coefficient, and elastic modulus. The results show that, with the increase of dry-wet cycles, the mass of the specimen increases slightly at 20 dry-wet cycles and then decreases gradually. Then, the stress-strain curve of geopolymer concrete can be divided into three stages: linear growth stage, deceleration growth stage, and slow decline stage, which correspond to the elastic deformation stage, elastic-plastic deformation stage, and crushing stage, respectively. The overall trend of the stress-strain curve is similar under different dry-wet cycles, and the peak stress decreases with the increase of dry-cycle. The relationship between stress and strain of geopolymer concrete samples with different salt solutions is similar, while their strength characteristics have changed obviously. Furthermore, with the increase of dry-wet cycles, the compressive strength and the relative elastic modulus of geopolymer concrete gradually decrease, which reflects that sulfate erosion will lead to the strength loss of geopolymer concrete, causing its internal damage, thus having adverse effects on it. Different salt solutions have the great influence on the mass loss rate, compressive strength, erosion resistance coefficient, and elastic modulus of geopolymer concrete. In detail, the mixed salt solution erosion results in the greatest damage to geopolymer concrete and accelerates the damage. Chloride salt solution erosion causes middle damage to geopolymer concrete. Compared with the other two salt solutions, sulfate solution erosion leads to the least damage to geopolymer concrete and then sulfate has a certain inhibitory effect on the damage of geopolymer concrete. In addition, based on the test results, the constitutive model considering dry-wet cycles damage of salt solution is proposed, and the correctness is verified. This study has a good guiding value for geopolymer concrete engineering in coastal areas.

Zangmu Bridge is a concrete‐filled steel tube (CFST) arch bridge along the Sichuan‐Tibet railway in Tibet, with a main span of 430 m. Owing to the unique temperature conditions in Tibet, there have been no large‐scale experimental studies on the thermal load design of CFST bridges in this area. Therefore, to determine the thermal load calculation parameters and thermal effects of Zangmu Bridge, a long‐term continuous field test was conducted to measure the temperature variations in a test arch with the same pipe diameter. The test results were then compared with current design specifications and relevant literature. Finally, the thermal effects in a CFST arch bridge were analysed using the finite element method. According to the results, the following recommendations were made: (1) the average temperature of concrete in the pipe after the formation of concrete strength should be used to calculate the closure temperature of CFST arch bridges in Tibet; however, the standard calculation formula was still applicable; (2) the daily average temperature in extreme weather should be taken as the maximum and minimum effective temperature; (3) we presented recommended values for the influence range and gradient temperature for a single large‐diameter pipe; and (4) a refined finite element model that included the arch base should be used to verify the temperature effects during bridge design.

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.

Six concrete beam-column frame sub-assemblages reinforced with basalt fiber-reinforced polymer (BFRP) bars in the frame beams were designed to investigate the collapse resistance after a middle column removal. Effect of parameters, including span to depth ratio of frame beams, prestressing, as well as material types of stirrups in the beams, on the collapse resistance of the sub-assemblages, was investigated. Experimental results showed that the initial stiffness of the frame beams was apparently lower due to low elastic modulus of BFRP bars. The collapse resistance of the sub-assemblages presented wave-like increasing tendency with the vertical displacement of the failed middle column, and it mainly attributed to the cracking or crushing of concrete and rupture of BFRP bars in the frame beams. Top longitudinal BFRP bars at the beam ends near to the side column (BESCs) and bottom longitudinal BFRP bars at the beam ends near to the middle column (BEMCs) kept tensile during the loading process, which played an important role in resisting structural collapse. Adjacent structural members such as frame beams and columns could provide horizontal reaction forces to constrain the free deformation of the residual sub-assemblages after the middle column failed, and it was beneficial to mitigate the structural collapse risk. The vertical deformation of the frame beams was nearly linear and proportional to the vertical displacement of the failed middle column. Finally, the dynamic increase factor (DIF) of collapse load was discussed using energy conservation method, and a calculation method of DIF for prestressed concrete frame structures was developed. It was suggested that the DIF values for the non-prestressed frame structures reinforced with BFRP bars in the beams should be taken as 2.0, while those for the prestressed sub-assemblages can be taken between 1.44 and 2.0.

To realize the real-time monitoring and evaluation of the bearing state such as force and deformation, and to meet the intelligent development needs of “self-sensing and self-evaluation” of engineering structures, this paper carried out a finite element simulation of the mechanical properties of spherical bearings and developed a new type of spherical force-measuring bearing based on the button type microsensors through the integration of structural monitoring technology. The simulation results show that the von Mises stress of the spherical bearing is mainly concentrated in the annular region where the edge of the spherical crown is located, and the magnitude of the force value decreases from the edge to the center gradually. The performance characteristics of spherical force-measuring bearings based on the button-type microsensor were studied by combining finite element simulation and experiments. The research results show that the sensitivity of this type of sensor is stable, and the growth trend of the measurement data is ideal with small dispersion, which is in line with the distribution law of the bearing internal force. The temperature loading test was carried out to study the effect of temperature on the bearing measurement accuracy. The fixed force value obtains the relationship between strain and temperature, and the minimum value method is proposed to calculate the temperature compensation coefficient and temperature compensation equation by fitting the slope of a straight line to improve the measurement accuracy of the sensor. Therefore, the research results have good value for engineering applications.