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.

In order to improve the durability of ordinary reinforced concrete beams, a new structure of ultra-high performance concrete (UHPC)-high performance concrete (HPC) composite beam was designed, and the flexural behavior of the UHPC-HPC composite beam after chloride corrosion was tested. The decrease mechanism of flexural capacity of the composite beam after chloride erosion was studied, and the effects of erosion degree, section form and pre-damage on the flexural behavior were analyzed. The yield strength reduction coefficient, cross-sectional area reduction coefficient of steel bar and pre-damage coefficient of concrete were introduced to propose the calculation method of flexural capacity of the UHPC-HPC composite beam after corrosion, and the feasibility of the calculation method was verified. Analysis results show that the main reasons for the decrease in the flexural capacity of the beam after corrosion are the decrease in the tensile strength of steel bars, the degradation of the stiffness and toughness of the beam, and the weakening of the crack resistance effect of steel fibers. The failure of the UHPC-HPC composite beam after corrosion is characterized by one main crack near the mid-span or two main cracks near the loading point. The stress process of the UHPC-HPC composite beam is divided into three stages: linear elasticity, crack development and yield. The concrete strain of the beam section basically conforms to the assumption of plane section. The longer the erosion time is, the more the cracking load and the flexural capacity reduce. When the beam is energized and eroded rapidly for 10 d, the reductions reach 16.2% and 10.9%, respectively. The T-beam cracks earlier than the rectangular beam, the cracking load of the former is 8.1% smaller than that of the later, and the stiffness decreases faster in the later stage after corrosion. The pre-damage significantly affects the overall stiffness of the beam, the overall stiffness decreases after pre-loading, and the pre-damage coefficient after the concrete damage is 0.984. The larger the corrosion rate is, the smaller the yield strength and the cross-sectional area reduction coefficient of the steel bar are, and the change trend conforms to the quadratic parabola. The calculated flexural capacity of the UHPC-HPC composite beam after corrosion is in good agreement with the measured value, the average ratio of the two is 0.998, and the standard deviation is 0.020.

To establish the fatigue crack initiation analysis method for U rib-cover plate welded joints of steel bridge decks, the conversion of cohesive parameters in the mixed loading mode was considered based on the Roe-Siegmund cyclic cohesive zone model, the secondary development of ABAQUS was carried out, and the VUMAT subroutine reflecting the cumulative fatigue damage was formed. The cohesive parameters of the material in the welding zone corresponding to the Q345 steel were obtained from the experimental data. Based on the Voronoi diagram method and the grain microstructure and mechanical characteristics of the welding zone, the microscopic grain structure at the U rib-cover plate weld toe was established. In addition, combined with the macroscopic 2D plane strain model, the multi-scale fatigue crack initiation was simulated. Combined with the equivalent structural stress method and the crack propagation theory of linear elastic fracture mechanics, the accumulated cohesive lengths under different stress levels were backpropagated considering the initial defect morphology and critical criterion of fatigue fracture, and then the calculation method for the crack initiation life was obtained. Analysis results show that when using the proposed method to simulate the crack initiation behavior at the weld toe of U rib-cover plate welded joint, the cracks initiate at the weld toe and propagate perpendicular to the top plate surface, forming a transcrystalline fracture mode. The stress distribution of the microscopic grain structure changes with crack initiation and short crack propagations, and as the microscopic grain structure distribution and mechanical characteristics change randomly, the details of short crack propagation paths and critical cycle numbers in the simulation results are not the same. The backpropagated accumulated cohesive length varies with the initial defect morphology ratio, the critical depth of long crack propagation, the distribution and mechanical characteristics of microscopic grain structure, and the stress amplitude. The fitted curves of accumulated cohesive length and equivalent structural stress amplitude obtained by considering the above factors are capable of obtaining the corresponding crack initiation lifes. Therefore, the established multi-scale fatigue crack initiation simulation analysis method can provide a new solution to obtain the fatigue crack initiation lifes of steel bridge decks.

JGJ 138—2016, СИ 3-78, YB 9082—2006, AISC 360-16, and YE Lie-ping's formulas were used to calculate the ultimate flexural capacities of 51 collected specimens of steel reinforced concrete (SRC) beams with rectangular sections. The calculated results were compared with the test values. The ranges of parameters of the collected specimens and the reasons for the calculation errors of the existing calculation methods were analyzed. The limitations of the existing calculation methods were discussed in terms of the calculation theory and other aspects. Theoretical derivations were performed, and a method for calculating the ultimate flexural capacities of SRC beams with rectangular sections was proposed, and the ultimate flexural capacities of the collected specimens were calculated by using the proposed method. Analysis results show that some deviations are found between the calculated values obtained by the existing calculation methods and the test values. The height value of the compression zone in СИ 3-78 is not appropriate, and the calculation error of this method increases with the increase in concrete strength. The impact of the relative relationship between the neutral axis and the position of the structural steel on the calculation results is not considered in JGJ 138—2016, and limitations exist. YB 9082—2006 and AISC 360-16 do not take into account the interaction between structural steel and concrete or the arrangement of the structural steel. The YE Lie-ping's formulas produce conservative results. The average ratio of the values calculated by the proposed method for the ultimate flexural capacity to the test values of specimens is 0.953, with a variance of 0.015. The calculated values agree well with the test values. The steel ratios of the collected SRC beam specimens range from 1.77% to 5.77%, which is smaller than the reasonable steel ratio range suggested by YB 9082—2006. Therefore, it is necessary to carry out further supplementary tests of specimens with high steel ratios in the future, so as to improve the calculation method for the ultimate flexural capacity of SRC beams with rectangular sections.

In response to the challenges of low efficiency and high cost of traditional manual dimensional inspection in face of massive bridge prefabricated components during the bridge construction, and to break through the accuracy and efficiency bottlenecks of existing data processing algorithms in the intelligent dimensional inspection using the terrestrial laser scanning (TLS) technology, an intelligent dimensional inspection framework for bridge steel prefabricated components was established based on the building information modeling (BIM)-TLS, including two links: geometric dimensional inspection and digital pre-assembly of components. The BIM point cloud processing technology was customized, and the reference point cloud model was constructed. The point cloud data were preprocessed by using the straight-through filtering, statistical outlier removal (SOR) filtering, voxel grid (VG), and other algorithms. The dimensional inspection index evaluation based on the k-nearest neighbor (kNN) algorithm was realized. Through the 3D-Harris feature point inspection, normal distributions transform (NDT) coarse registration, and iterative closet point (ICP) fine registration, a fast registration intelligent dimensional inspection strategy based on the Harris feature and NDT-ICP algorithm was proposed and applied to the intelligent dimensional inspection of steel box arch prefabricated components of a large-span arch beam composite structure in combination with the engineering requirements. Research results show that the maximum deviations of the proposed intelligent inspection method for the dimensional inspection of two steel box arches at adjacent segments are 1.689 and 1.571 mm, respectively, and meet the requirement of the manufacturing deviation (less than 2 mm). Compared with the traditional NDT-ICP algorithm, the proposed method improves the overall registration accuracy of the point cloud by 35.3% and the efficiency by 61.88%. It can be seen that the method is efficient, and the results are accurate. It promotes the intelligence of the geometric dimensional inspection of steel prefabricated components. Based on the method, the maximum inspection assembly deviation of the digital pre-assembly monitoring point for the arch rib is 1.953 3 mm, and meets the requirement of the assembly deviation (less than 2 mm). The method realizes the accurate deviation inspection. It provides a good guarantee for the smooth erection of subsequent bridge positions and a reference for dimensional inspections of similar structures.

In order to solve the fatigue cracking problem of the diaphragm arc-shape cutouts in the orthotropic steel bridge decks due to vehicle-induced vibration and cyclical wheel load under prolonged service conditions, two kinds of reinforcement methods, including carbon fiber reinforced polymer (CFRP) sheets covering crack-stop holes method and shape memory alloys (SMA)/CFRP composite patches covering crack-stop holes method which introduced prestress by activating SMA were proposed. The static and fatigue loading tests were carried out on the repaired diaphragm specimens, the corresponding finite element models were established for numerical simulation and parameter analysis of different reinforcement methods, and the repair effects of different reinforcement methods were compared. Research results show that, after bonding CFRP sheets and SMA/CFRP composite patches on the basis of crack-stop holes, the stresses at the hole edges of diaphragms reduce by 12.46% and 44.90%, respectively, and the fatigue lives of diaphragms repaired with CFRP sheets and SMA/CFRP composite patches are 2.57 and 5.07 times that of diaphragms repaired simply with the crack-stop holes, respectively. Both the two methods can effectively improve the local stiffnesses of the cracked region, and alleviate the stress concentration and improve the fatigue performance of the cracked diaphragms. When repairing with CFRP sheets, increasing the number of CFRP sheets layers can significantly reduce the stress and stress concentration on the diaphragm. To guarantee the bonding performance between CFRP sheets and steel plates, however, it is appropriate to apply 2-3 layers of CFRP sheets in practical applications. When repairing with SMA/CFRP composite patches, the stress concentration on steel plates exhibits an approximately linear decreasing trend with the increase of SMA wire actived stress. Consequently, the repair effect can be effectively enhanced by increasing the SMA wire actived stress in practical engineering.

In order to determine the representative values of sunshine temperature differences of concrete single-box multi-cell box girders in different regions, outdoor sunshine temperature field test models were established in Shannan of Xizang, Tongchuan of Shaanxi and Laibin of Guangxi, respectively, and a large number of temperature sensors and meteorological collectors were installed at the same time. The meteorological variability in Shannan, Tongchuan and Laibin was summarized through the on-site measured data, and the formulae for calculating the temperature difference among box girders in Shannan, Tongchuan and Laibin were proposed through the step-by-step regression of the long-term box girder test temperature and the hour-by-hour meteorological data. The meteorological data from 1955 to 2016 in 6 prefecture-level cities in Xizang, 10 prefecture-level cities in Shaanxi, and 14 prefecture-level cities in Guangxi were surveyed, and the daily meteorological data were decomposed into hour-by-hour meteorological data for the calculation of the temperature difference. Based on the suprathreshold distribution model, the representative values of the temperature action in three provinces with a reproduction period of 50 years were obtained, and the temperature action distribution maps were drawn. Research results show that the measured vertical temperature difference of sunny side web, vertical temperature difference of middle web, lateral temperature difference of top plate and lateral temperature difference of bottom plate of the box girder model are in descending order from Shannan, Tongchuan to Laibin, which shows that both the vertical and lateral temperature differences of box girders in different regions of China are differentiated by the influence of geographic location. The lateral temperature difference of the top plate of the concrete box girder in the sunny side is higher than that of the bottom plate, specifically by 30.7%, 23.2% and 11.1% in Shannan, Tongchuan and Laibin, respectively. The vertical temperature difference of the middle web can reach up to 10.5 ℃ and the lateral temperature difference of the top plate can reach up to 20.3 ℃ in Xizang, Shaanxi and Guangxi, showing that the sunshine effect on concrete bridge varies significantly by region.

To enhance the practicality of magnetic flux leakage detection for high-strength steel wires in bridge cables, the corrosion and stress single factor tests, as well as three-stage interaction tests of pre-corrosion-fatigue-corrosion and pre-fatigue-corrosion-fatigue were conducted, and the mechanism for the influence of corrosion-fatigue coupling effect on the self-magnetic flux leakage signal was explained. Research results show that the extreme self-magnetic flux leakage signals in the corrosion area increase with the corrosion time, and the variation characteristics are becoming more and more obvious. The maximum variation in the abnormal self-magnetic flux leakage signals caused by the corrosion defect can reach up to 50 000 nT. As the fatigue loading cycle number increases, the self-magnetic flux leakage signal of non-corroded high-strength steels wire is on an overall increasing trend before getting stabilized. When the fatigue loading cycle number exceeds 10 000, the increasing rate of magnetic field intensity decreases and tends to be stable. The alternating stress field applied after the pre-corrosion weakens the self-magnetic flux leakage signal caused by the corrosion defect, and the variation in the magnetic field signal after the second corrosion is related to the degree of pre-corrosion. Under the fatigue load after the pre-corrosion for 9 h, and then in the second corrosion for 3 h, the strength of the self-magnetic flux leakage signal reduces by 32% compared with that in the single corrosion for 12 h. Applying a pre-fatigue alternating stress field can strengthen the magnetic field, leading to an increase in the extreme self-magnetic flux leakage signal after the corrosion. When the pre-fatigue loading cycle number increases from 1 000 to 100 000, the strength of the self-magnetic flux leakage signal increases by 30%. It follows that the abnormal self-magnetic flux leakage signals of high-strength steel wires caused by the initial corrosion can be masked by the fatigue effect, making it difficult to reflect the detection effect of self-magnetic flux leakage of high-strength steel wires by just considering a single factor of variation in the corrosion or stress. Therefore, it is necessary to comprehensively consider the corrosion-fatigue coupling effect, so as to obtain the variation laws of self-magnetic flux leakage signals of high-strength steel wires in bridge cables, thereby providing an analytical basis for the non-destructive test of bridge cables.

In order to improve the concrete cracking defect in the negative moment regions of steel-concrete composite girders, the engineered cementitious composite (ECC) and ultra-high performance concrete (UHPC) were introduced to replace the normal concrete (NC) to form the steel-ECC/UHPC composite girders. The tests of static mechanical properties in the negative moment regions were carried out, involving one steel-NC composite girder, one steel-ECC composite girder, and two steel-UHPC composite girders. The finite element analysis method was utilized to compare the strain, crack propagation, and distribution characteristics of different types of concretes. The influences of concrete type and reinforcement on the failure mode, bearing capacity and deformation capacity of steel-concrete composite girders were analyzed. Research results show that the steel-concrete composite girders have good overall cooperative performance under negative moments, and the failure modes are all bending failure. Cracks in the ECC and UHPC are delicate, especially in the ECC. Compared with the steel-NC composite girder, the cracking loads of steel-ECC and steel-UHPC composite girders increase by 2.00 and 2.75 times, the flexural stiffnesses increase by 17.23% and 35.73%, and the flexural capacities increase by 9.00% and 6.81%, respectively. Therefore, the UHPC has stronger crack resistance, effectively improving the crack resistance of bridge decks in negative moment region of the steel-concrete composite girders. Moreover, using the ECC and UHPC to replace the NC can enhance the flexural stiffness and bearing capacity of steel-concrete composite girders. There is no significant difference in the cracking load and early stiffness between the reinforced and unreinforced steel-UHPC composite girders. When the unreinforced steel-UHPC composite girder fails, the through cracks form, and its bearing capacity decreases by 13.39% compared to the reinforced steel-UHPC composite girder. As the ECC strength increases, the bearing capacity of steel-ECC composite girder improves significantly. The influence of UHPC strength on the bearing capacity of steel-UHPC composite girder is not obvious. The impact of reinforcement ratio on the bearing capacity of steel-UHPC composite girder can be divided into two stages. When the reinforcement ratio is below 1.6%, the bearing capacity increases significantly, and when it exceeds 1.6%, the growth rate of bearing capacity slows down.

In order to enhance the evaluation accuracy of the ultimate bearing capacity of stayed cables, the influence of corrosion damage on the stayed cables was considered, the mechanical property model of corroded steel wires was established, and the mechanical properties of intact and corroded steel wires were simulated. Based on the combined action of three typical cross-section corrosion distribution models, and three typical corrosion distribution model types along the cable length direction, the corrosion degrees at different positions in the stayed cable were analyzed, and the distribution law of the corrosion in the stayed cable was studied. The Monte Carlo method was used to simulate the mechanical properties of the steel wire in the cable under different corrosion degrees, and the ultimate bearing capacity of the cable was finally obtained, as well as the number of broken wires when the stayed cable reached the ultimate bearing capacity. The correlation among the ultimate bearing capacity, the number of broken wires, the corrosion depth, and the cross-section corrosion rate of the stayed cable was statistically analyzed. The influence of corrosion distribution law was analyzed. Analysis results show that under different corrosion distribution conditions, when the corroded stayed cable reaches the ultimate bearing capacity, the sample mean difference of the numbers of broken wires may reach about three times, while the sample mean change of the ultimate bearing capacity of the stayed cable can reach about 20%. When the stayed cable reaches the ultimate bearing capacity, the number of broken wires increases with the increase of corrosion degree. But the correlation between the number of broken wires and the ultimate bearing capacity is poor, even only 0.014 under some corrosion distribution conditions. In order to ensure the safety and reliability of the stayed cable, the number of broken wires should not be used as a technical index to evaluate the bearing capacity of cables.

To determine the reasonable load limit of steel bridge decks, the multi-scale finite element models were built for steel bridge decks. With the weigh-in-motion (WIM) and Monte Carlo method, the stochastic traffic flows were generated and the finite element model was dynamically loaded. Stochastic fatigue stress spectra were acquired by rain flow counting method. According to reliability theory and cumulative fatigue damage theory, the fatigue reliabilities of typical details were calculated, and then the fatigue reliability-based load limit method was proposed for steel bridge decks. Taking the steel bridge deck of a sea-crossing cable-stayed bridge as an example, the fatigue reliabilities of typical details were assessed respectively based on the WIM data in 12 consecutive months. Considering the linear annual growth coefficients of traffic volume and load level, load limit values were determined for steel bridge decks under different traffic conditions. Research results show that the fatigue reliability indices of steel bridge decks are higher than the target fatigue reliability indices under current traffic conditions. Traffic volume and load level have great influence on the fatigue reliability of steel bridge decks. Considering that the linear annual growth coefficient of the traffic volume is 2.0% or the linear annual growth coefficient of the load level is 0.4%, the fatigue reliability indices of some details are lower than the target fatigue reliability indices during the design service life. Considering that the linear annual growth coefficient of traffic volume is 3.0% and the linear annual growth coefficient of load level is 0.6%, the fatigue reliability indices are lower than the target fatigue reliability indices under the current load limit of 49.0 t. When the load limit is 36.5 t, the fatigue reliabilities can meet the fatigue safety requirements. At the current load level, the maximum average daily truck traffic of the single lane is 3 820 veh. When the traffic volume increases significantly during the operation, the fatigue damage detection should be strengthened for the steel bridge decks, and traffic diversion or bridge load limit measures should be taken if it is necessary.