The application, acceptance, review, and funding status of the transportation and vehicle engineering discipline of the National Natural Science Foundation of China (NSFC) in 2023 were summarized, the organized scientific research efforts in the discipline were overviewed, and a detailed interpretation of the key funding directions for the coming 2024 was provided. Focusing on the development goals of goal orientation, harmonious development, interdisciplinary and service for the future, the discipline will continue to strengthen the demand-driven and problem-oriented research, promote organized scientific research, and drive the field development by discipline construction. Focusing on the national defense security and major national needs, the discipline will continue to identify the major and key research problems, providing a solid foundation for future major competitive projects and the overall planning of basic research and applied basic research. In 2024, the discipline will continue to prioritize funding for the specific domains to propel their developments. These domains include comprehensive three-dimensional transportation multi-network integration, high-speed maglev systems operating at 600 km·h^-1 speed level, autonomous driving evaluation and verification, active safety control for distributed electric drive vehicles, special vehicles with reconfigurable or variable structure, coordinated operation of transportation systems in hub airport flight areas, ultra-low-temperature energy material's water transport or pipeline transport, resource planning and coordinated operation of national airspace system, and reusable space-to-sky round-trip transportation systems.

The research progresses of steel bridge fatigue were systematically generalized and analyzed, and the innovative achievements of steel bridge fatigue load, fatigue mechanism, anti-fatigue design method, fatigue safety monitoring and evaluation, and fatigue safety maintenance and other aspects were summarized. The technical challenges were deeply discussed for steel bridge construction and service maintenance, and the development tendencies were explored for the innovative research of steel bridges. Research results show that (1) the developed vehicle, train, and temperature fatigue load models are matched with the characteristics of traffic loads at bridge sites, structural types and design service life, promoting the improvement of the anti-fatigue design theory for long-lasting steel bridges. (2) The actual fatigue damage of steel bridges can be better reflected by the surfing calculation model derived by the vehicle-temperature coupling fatigue stress. The cumulative fatigue damage under the coupling effect of temperature and vehicles is 10%-15% higher than when only considering the effect of vehicles. (3) A new paradigm of fatigue mechanism research, which integrates physical fatigue test, digital fatigue test and in-situ fatigue test techniques, has emerged, partially altering the traditional understanding of fatigue. The influence laws of distortion-induced deformation ratio and stress ratio on the distortion-induced fatigue behavior and detail fatigue strength were investigated. It is found that the fatigue strength of cable steel wires plummets under the condition of high stress ratio in actual bridges. The objective law is revealed that when the strength grade of cable steel wires increases from 1 670 MPa to 2 060 MPa, the fatigue strength first increases and then decreases. The objective fact is clarified that the fatigue strength of weathering steel bridge details does not decrease after the corrosion. (4) The construction of whole bridge multi-physical field, multi-scale, and multi-probability fatigue twin model has been gradually realized, promoting the advent of steel bridge fatigue metaverse technology characterized by data originality, data interaction, and the symbiosis of virtuality and reality. (5) To solve the design issues of steel bridge details working with fatigue cracks, it is necessary to take the fatigue cracks as the key technical index controlling the structural function and safety, and to adopt the damage tolerance theory for the anti-fatigue design of steel bridges. (6) To break through the technical bottlenecks of crack perception and load acquisition, it is necessary to deeply integrate new artificial intelligence technologies such as acoustic emission, digital filming/photography, computer vision technology, and deep learning, and to create a digital monitoring database for fatigue load and damage of steel bridges, providing comprehensive information for researching on the fatigue mechanisms, design, and evaluation methods of steel bridges. (7) To solve the technical issue that traditional linear cumulative damage evaluation models can not predict the fatigue life of cracked details, it is necessary to establish a digital fatigue evaluation model for steel bridges based on digital twin technology. This will enable precise digital description of fatigue cracks across scales and throughout the entire process, and build an integrated digital fatigue evaluation platform for steel bridges, consisting of intelligent monitoring, twin simulation, intelligent evaluation, and smart decision. (8) Cold reinforcement technique can realize targeted and efficient reinforcement for fatigue cracks in steel bridges with zero or minimal damage to the original structure, allowing implementation without interrupting traffic flow, and has a broad application prospects. (9) Cold reinforcement, hot reinforcement, and cold-hot hybrid reinforcement techniques can be utilized flexibly for steel bridges with different fatigue damage degrees, performance enhancement requirements, and life extension goals, to achieve toughening and light-weighting in the fatigue maintenance of steel bridges.

The measurement methods, principles, and influencing factors during engineering applications of three non-contact displacement measurement technologies were systematically summarized, such as the visual measurement, microwave radar, and laser vibration measurement. The innovative achievements of non-contact displacement measurement technologies in the dynamic displacement measurement, modal identification, and cable tension testing in bridge engineering were introduced. Moreover, the key challenges faced by the non-contact displacement measurement and future research directions were discussed. It is found that non-contact displacement measurement methods can obtain real-time dynamic displacement, natural vibration frequency, modal shape, and other information about bridge structures. The measurement accuracy is affected by multiple factors such as the hardware, algorithm, measurement distance, and environmental conditions. The visual measurement technology makes it easy to achieve real-time in-plane displacement measurement of multiple targets at a low cost, but it is sensitive to change in environmental conditions and generally requires target installation. Therefore, it is suitable for short-distance and long-term or long-distance and short-term displacement monitoring. The microwave radar has the characteristics of strong anti-weather interference capability, long measurement distance (up to 2 km), acceptable cost, all-weather all-time operation, and long-term monitoring. Generally, corner reflectors are needed to improve the accuracy of radial displacement measurement. The laser vibration measurement technology has the micrometer-level displacement measurement accuracy and strong resistance to electromagnetic interference. However, it is difficult to achieve long-distance and multi-target synchronous measurements with poor penetration and is easily affected by environmental conditions. In addition, its equipment is expensive, and thus it is suitable for short-term radial displacement monitoring. Suitable non-contact measurement methods should be selected according to different needs of bridge structures for long-term and short-term monitoring, measurement distance, environmental conditions, single (multiple) target monitoring, and measurement accuracy. In the future, the ability to perform long-distance and multi-target synchronous measurements can be enhanced by improving the performance of the hardware system. Various disturbance correction algorithms for adaptive environments (lighting and atmosphere) can be developed to improve the displacement measurement accuracy and reliability. Furthermore, it is necessary to integrate the visual measurement, microwave radars, and laser vibration measurement technologies with testing methods such as accelerometers, total stations, and global position system (GPS) for multi-source information fusion, thus ensuring mutual calibration to reduce uncertainty, improving the measurement robustness under different environmental conditions, and achieving all-weather three-dimensional testing.

The research progress of ultra-high performance fiber reinforced cementitious (UHPFRC) composite material composite steel bridge decks was summarized and analyzed from three aspects, including the material selection for the high resilience composite layer, interface force transfer mechanism and damage accumulation mechanism, and design method and engineering practice. The effects of fiber type and fiber content on the axial tensile and flexural properties of the UHPFRC were summarized. Several constitutive models were determined for the structural analysis of the composite steel bridge deck. Technical characteristics were compared and analyzed for the interface design methods adopting hot, cold, and hybrid connections. The experimental and theoretical achievements in the force transfer mechanism of adhesive interface, shear connector interface with cold connection, and hybrid connection interface were summarized. The research results of rational configuration, design method, specification, and engineering practice were summarized for the composite steel bridge deck based on the cold connection design concept. The innovation and development directions of long lasting composite steel bridge decks were also discussed. Research results show that the addition of single or hybrid fibers can comprehensively improve the strain strengthening ability, flexural deformation ability, fracture resistance, crack width control ability, and fatigue resistance of the UHPFRC. The simplified three-linear constitutive model of UHPFRC under the axial tension powerfully supports the design and calculation of steel bridge decks. The elastoplastic damage constitutive model can describe the irreversible fatigue damage accumulation. The toughening effect and reliability of the composite interface with cold connection are verified. The innovative shear connector can both improve the composition effect and toughen the UHPFRC layer. The hybrid connection interface has comprehensive technical advantages such as reducing the local stress concentration, improving the overall shear stiffness, improving the force transfer of the interface, and enhancing the construction efficiency. The cohesive interface constitutive model can realize the inversion analysis of the cumulative damage of interface with cold connection, and the interface damage prediction results are accurate and reliable. The UHPFRC composite steel bridge deck based on the cold connection can effectively improve the local stiffness of the steel bridge deck. The related design method can support the formulation of standards and engineering practices. The cost effectiveness of the UHPFRC, as well as the efficiency and reliability of the interface connection should be improved, so as to support the design and construction of composite steel bridge decks with long life, high resilience, lightweight, easy maintenance, and low energy consumption.

To achieve effective reinforcement of fatigue crack at weld root on rib-to-deck, an internal welding reinforcement method was proposed to meet the requirements of in-service steel bridge decks, and automated welding robots and associated key equipment were developed. Four test models were designed to study the effectiveness and applicability of the method and equipment. The cracking mode of fatigue crack at weld root on rib-to-deck was validated. The developed specialized welding equipment for internal welding reinforcement was used internally within the rib, and fatigue failure tests on the reinforced structure were conducted. The results of experiment and finite element simulation were compared. The fatigue performance of the structure after reinforcement was analyzed, and the effectiveness of internal welding reinforcement method was confirmed. Research results indicate that the internal welding reinforcement method can transform the existing weld root cracks into internal defects. The developed equipment enables in-site reinforcement, effectively suppressing the expansion of fatigue cracks, and enhancing the fatigue lives of the cracked welded joints by 66%-157%. Due to the different degrees of fatigue damage accumulation in various cracking modes, a transition in the dominant cracking mode of the welded joints occurs after reinforcement. For welded joints containing multiple cracking modes, the remaining fatigue life after reinforcement is closely related to the actual fatigue damage accumulation levels of each cracking mode and the degree of disturbance of reinforcement methods on the stress characteristics of each cracking mode.

In order to study the fatigue performance of concrete-filled steel tubular-KK (CFST-KK) joint, a fatigue test on CFST-KK joint models was conducted, and the stress distribution pattern and fatigue performance evolution of CFST-KK joints were analyzed. A solid finite element (FE) model of CFST-KK joint was established. In combination with the results of the test and FE models, the difference in the fatigue performance between the CFST-KK joint and the concrete-filled steel tubular-K (CFST-K) joint was revealed, the influences of different parameters on the fatigue performance of KK joint were analyzed, and an appropriate fatigue life evaluation method for the CFST-KK joint was discussed. Research results show that the maximum hot spot stress of CFST-KK joint calculated by the quadratic extrapolation method is located 15° away from the crown point on the chord side of tension brace to the chord intersecting weld towards the outer saddle point. In calculating the stress concentration factor (SCF) of CFST-KK joint, the nominal stress of the brace only takes into account the influence of axial force and in-plane bending moment regardless of the impact of out-of-plane bending moment, and the SCF of CFST-KK joint is 6.36, 80.2% higher than that of CFST-K joint. The fatigue crack in the CFST-K joint originates at the location with the highest stress concentration, extends towards the two sides and wall thickness of the chord along the weld toe root during repeated loading, and expands slightly faster towards the outer saddle point than the inner saddle point. However, it does not penetrate the chord wall after stopping the repeated loading. The fatigue resistance of CFST-KK joint differs significantly from that of CFST-K joint, primarily due to the presence of out-of-plane bending moment in the brace and the spatial interaction between the braces. Filling the tube with concrete can enhance the radial stiffness of CFST-KK joint and reduce the stress concentration. Augmenting the angle beyond the branch face can enhance the spatial interaction between the braces. Taking into account the impact of filled concrete, the hot spot stress and fatigue life curve of CFST-K joint has high precision in assessing the fatigue life of CFST-KK joint.