Key deterioration mechanisms and technical enhancement strategies for improving the service performance of steel-concrete composite girder bridges incomplex environments were systematically reviewed and summarized. At the material level, the degradation characteristics of steel and concrete under the combined effects of chloride ingress, freeze-thaw cycles, and fatigue loading were reviewed. The main deterioration mechanisms, including cross-sectional loss, stress concentration, and microcrack evolution, were analyzed. The degradation modes of shear connectors and the characteristics of interface damage were summarized, revealing the key failure mechanisms under corrosion-fatigue interactions. The effects of typical degradation behaviors on structural bearing capacity and ductility were analyzed. Engineering measures to improve the durability of composite girder bridges were summarized, including the use of new materials such as ultra-high-performance concrete (UHPC), weathering steel, and fiber-reinforced polymer (FRP) composites, as well as improved sealing of prefabricated interfaces and joints, optimized drainage and ventilation systems, and techniques for concrete surface protection and reinforcement corrosion inhibition. These measures establish a durability enhancement pathway based on the coordinated control of materials, structure, environment, and surface conditions. The results show that the durability of steel-concrete composite girder bridges is influenced by environmental conditions and structural detailing, while existing code-based design methods are insufficient to account for uncertainties arising from the coupled effects of environmental and loading factors. Future research may focus on modeling multi-factor coupled deterioration mechanisms, promoting the engineering application and standardized evaluation of high-performance materials, developing controllable connection configurations and interface protection systems, and establishing an integrated life-cycle monitoring-prediction-intervention framework based on intelligent sensing technologies. These efforts will contribute to the development of a durability design theory and evaluation framework for bridges over their full life cycle.

To integrate dispersed studies and clarify the mechanisms underlying performance enhancement, a systematic review of over 110 studies in China and abroad was conducted to promote the practical engineering application of fiber-reinforced cementitious composite (FRCC)-encased concrete-filled steel tube (CFST) columns (hereafter referred to as FRCC-CFST columns) in steel-concrete composite bridges. Following the sequence of "material → interface → member → design → application", the research progress and practical applications of three typical FRCC encasing materials, including engineered cementitious composites (ECC), ultra-high performance concrete (UHPC), and hybrid fiber-reinforced cementitious composites (HFC), in FRCC-CFST columns were comprehensively summarized and analyzed. The results indicate that, at the material level, the three types of FRCC exhibit distinct advantages. ECC shows the best ductility, UHPC provides the highest load-bearing capacity, and HFC demonstrates intermediate overall performance. At the interface level, the high bonding strength and fiber-bridging mechanisms of FRCC help delay spalling of the encasement and enhance composite action. Measures such as installing shear studs, adding interface reinforcement, or increasing interface roughness can effectively enhance the steel tube-FRCC bond strength and improve the failure mode. At the member level, FRCC-CFST columns exhibit significantly superior performance under various conditions, including axial compression, eccentric compression, bending, shear, seismic, impact, and high temperature, compared with conventional CFST composite columns encased with ordinary concrete. The degree of performance enhancement is closely related to the FRCC type and structural confinement. At the design level, some mechanical models have demonstrated good predictive capability. However, existing design codes do not fully consider the high ductility and interface characteristics of FRCC, resulting in conservative load-bearing capacity evaluation. At the application level, UHPC-encased CFST columns have been validated in engineering practice, such as the Haixin Bridge in Guangzhou. In contrast, ECC- and HFC-encased CFST columns are still mostly in the experimental stage, limited by factors such as cost, construction adaptability, and the lack of design specifications. Future research should focus on the stability of medium and long columns, multi-hazard coupled responses, and interface cooperative mechanisms, so as to promote the development of a complete design theory and engineering application system and facilitate the standardized and large-scale application of FRCC-CFST columns.

To enhance the material utilization efficiency in the negative moment regions of steel-concrete composite beams, a double composite beam with constrained shear connectors was proposed. Flexural tests were carried out on one simply supported beam and one continuous beam. Analysis was performed on the failure mode, load-bearing capacity, interface slip, and strain distribution characteristics of the steel-concrete composite beam with constrained shear connectors. Based on finite element simulation, the interfacial mechanical mechanism and plastic hinge formation mechanism of the steel-concrete double composite beam were revealed. The stiffness degradation law was further explored for the steel-concrete double composite beam by establishing a characteristic-point-based mid-span load-deflection curve model. The research results show that the failure mode of the steel-concrete double composite beam is tensile-shear failure with inclined cracks at the inflection point. Cracks in the concrete at the bottom of the slab in the negative moment region are fine and few in number. Compared with conventional steel-concrete continuous composite beams, the double composite beam exhibits increases of 49% in load-bearing capacity and 67% in stiffness. Stiffness degradation of the double composite beam exhibits a three-stage characteristic: stable stiffness in the elastic stage, moderate stiffness degradation in the elastoplastic stage, and significant stiffness degradation in the ultimate plastic stage. The theoretical model is suitable for evaluating the deformation capacity and overall stiffness degradation law of the double composite beam. Numerical results indicate that the flexural stiffness of the intermediate support section of the double composite beam is 1.66 times that of the mid-span section. During loading, the plastic hinge forms earlier in the mid-span than at the support. The shear connectors on the additional steel plate bear 34% of the interfacial shear force in the negative moment region, thereby enhancing the interfacial shear stiffness. Under a large deformation, the working state coefficient of the additional steel plate interface reaches 0.49, indicating significantly improved utilization efficiency. The double composite structure fully leverages the complementary characteristics of high tensile strength of steel and high compressive strength of concrete, improves the crack resistance of the bridge deck in the negative moment region of the steel-concrete composite beam, and fundamentally resolves the engineering challenge of concrete slab cracking and low material utilization efficiency in the negative moment region of steel-concrete composite beams.

To investigate the bearing capacity of a novel steel truss web member-concrete composite arch joint, and to provide a basis for arrangement of shear connectors of the joint, tests were conducted on four joint specimens with different shear connectors based on the engineering background of the Wumengshan Bridge. The failure modes and bearing capacity of the joint specimens were examined. The force transmission performance of the different shear connectors was comparatively analyzed. The applicability of existing code-based methods for calculating the bearing capacity of the shear connectors was comparatively analyzed. The analytical results show that all joint specimens exhibit buckling failure in the compressed web members and the gusset plates at the connections of the compressed web members. The interfacial bonding between the gusset plate and the concrete remains intact, with no signs of failure observed. All joint specimens exhibit bearing capacities exceeding twice the design load, thereby meeting the design requirements. The shear connectors effectively transfer the axial force from the steel chord, which is applied by a web member, to the concrete chord, and the most significant force transmission occurs within a range equal to one width of web member below the joint center. Penetrating steel bars present a superior force transmission performance compared to studs, and the difference in force transmission between a specimen with only penetrating steel bars and that with both penetrating steel bars and studs is very small. The recommended specifications applicable to the calculation of shear bearing capacities of penetrating steel bars and studs are presented. The research findings can provide reference for the design of steel truss web member-concrete composite truss arch joints.

To enhance the mechanical performance of double-bolt connectors in steel-concrete composite structures, optimization was performed on the configuration of existing double-bolt connectors. Push-out specimens of double-bolt connectors with diameters of M16, M20, and M24 were designed and fabricated, including both original specimens and optimized specimens. Push-out tests were then conducted. Based on the measured shear force-relative slip curves and failure modes of connectors, the shear capacity, peak slip, and shear stiffness of the optimized double-bolt connectors were systematically evaluated. Experimental results show that the final failure mode of all push-out specimens is shear fracture of the bolt shanks, and the fracture surfaces exhibit typical brittle fracture features. For the optimized double-bolt connectors, only slight cracking occurs in the concrete at the lower side, and no crushing or spalling is observed. Compared with those of the original double-bolt connectors, the shear capacity of the optimized double-bolt connectors increases by approximately 30%, and the peak slip increases by approximately 70%, while the average shear stiffness decreases by approximately 65%. In the optimized double-bolt connectors, a steel cushion plate was added between the short bolt and the sleeve, so that the shear plane was located in the unthreaded region of the short bolt shank. This increases the effective shear area and therefore improves the shear capacity of the connectors. The introduction of the steel cushion plate causes a large bending deformation of the short bolt shank during shear loading, which markedly enhances the ductility of the connectors but also leads to a reduction in their shear stiffness. The proposed calculation methods for the shear capacity and shear stiffness can provide theoretical reference for the application of double-bolt connectors in steel-concrete composite structures.

This paper aims to investigate the effect of the high-strength bolt crack arresting method on improving fatigue resistance performance of steel tubular K-joints. Both model tests and combined finite element simulations by adopting MSC.MARC and MSC.Fatigue were carried out, and the hot-spot stress distribution and fatigue evolution process of steel tubular K-joints improved by the high-strength bolt crack arresting method were revealed. Additionally, a calculation method for the stress concentration relief factor and a fatigue life prediction formula for steel tubular K-joints improved by the high-strength bolt crack arresting method were proposed. Finally, the effectiveness of the high-strength bolt crack arresting method in improving the fatigue resistance performance of steel tubular K-joints was evaluated by utilizing S-N curves. The results indicate that the fatigue evolution process of K-joints improved by the drilling crack arresting method and high-strength bolt crack arresting method can be divided into six stages, including crack initiation, crack propagation, drilling crack arresting/high-strength bolt crack arresting, secondary crack initiation, secondary crack propagation, and specimen failure. The combined finite element simulations of steel tubular K-joints improved by the high-strength bolt crack arresting method demonstrate a maximum error of only 11.9%. For steel tubular K-joints improved by the high-strength bolt crack arresting method, the calculation formula for the stress concentration relief factor and fatigue life prediction formula exhibit maximum deviations of 17.8% and 19.7% respectively compared with experimental or finite element simulation results. The fatigue strength of steel tubular K-joints improved by the drilling crack arresting method is 58.9% lower than the API standard recommended value, and thus this method can only be employed as a temporary reinforcement measure. In contrast, the fatigue strength of steel tubular K-joints improved by the high-strength bolt crack arresting method exceeds the API recommended value by 16.0%-34.4%, making this method suitable for long-term reinforcement.

To overcome curvature locking in conventional displacement-based finite element methods for analyzing the long-term mechanical behavior of steel-concrete composite beams, and to improve computational accuracy and efficiency, an exact finite element method that accounts for interfacial slip between the two beam layers, shear deformation of beam layers, and the effects of concrete shrinkage and creep was proposed. Based on the fundamental equations of elasticity and a linear viscoelastic constitutive model for concrete creep, the governing differential equations for the composite beam element were derived and solved analytically. The exact element stiffness matrix and equivalent load matrix were formulated using the direct stiffness method, and a corresponding numerical program was developed. The proposed method was validated using three representative examples, followed by a parametric study. The results indicate that the proposed finite element method can accurately predict the time-dependent mechanical response of steel-concrete composite beams while accounting for both shear deformation and interfacial slip. High accuracy can still be achieved with a relatively coarse mesh and a limited number of time steps in shrinkage and creep analysis. Compared with the analytical solution, the error in deflection at 365 d is less than 3.2%, while the computational efficiency and applicability are significantly improved. In comparison with a finite element method that neglects shear deformation, the proposed method reduces the error by more than 10%. The proposed method therefore provides an efficient and reliable computational tool for the long-term performance analysis and engineering design of steel-concrete composite beams.

To investigate the influence of diaphragm stiffness and number on the distortional behavior of composite box girders with corrugated steel webs (CSWs), a distortional beam element (B2D-CSW) that incorporates both diaphragm stiffness and shear deformation effects was developed. Based on the generalized coordinate method, expressions for distortional warping displacement in composite box sections with CSWs were formulated, incorporating the influence of distortional shear force on shear deformation. The physical relationship between distortional shear force and distortional bimoment was derived theoretically. By enforcing displacement compatibility between diaphragms and the composite box section, deformation expressions for different diaphragm types and their geometric relationships with the distortion angle were established, thus revealing their mechanism for resisting distortional deformation. Using the energy variational method, governing differential equations for composite box girders with CSWs that account for distortional shear deformation were derived, and interpolation functions for generalized displacements were constructed based on homogeneous solutions. Based on the finite element method, a two-node, four-degree-of-freedom distortional beam element considering distortional shear deformation was developed, and the stiffness matrix and equivalent nodal load vector considering diaphragm stiffness were derived. Through numerical examples, the computational accuracy and wide applicability of the proposed B2D-CSW beam element were verified. The results indicate that, compared with solid finite element models, the B2D-CSW beam element can accurately predict the distortional response of composite box girders with CSWs under varying diaphragm stiffness and number of diaphragms, using only a small number of elements and thus significantly improving modeling and computational efficiency. The analysis shows that the anti-distortional stiffness of diaphragms provides significant elastic restraint on the distortional deformation of composite box girders with CSWs. As the diaphragm stiffness or number reaches a critical threshold, the restraining effect on the distortional deformation of the main girder tends to stabilize. The proposed B2D-CSW beam element provides a reliable computational method for the design and analysis of diaphragms in continuous prestressed concrete (PC) composite box girder bridges with CSWs.

To accurately calculate the vertical shear stress of curved composite steel box girders with corrugated webs and quantify the contribution of each component effect, a calculation method of shear stress was proposed, which simultaneously considered the flexural resistance of corrugated steel webs, initial curvature, and curvature variation along the girder width. Based on the theory of shells of revolution, analytical formulas for shear stress were derived, including the components of bending, free torsion, restrained torsional warping, and distortional warping. The governing differential equations were established by the energy variational method and solved by the finite difference method. Through parametric analysis of structural horizontal curvature, loading position, and cross-sectional dimensions, the distribution laws and key characteristic indices of shear stress for this type of curved girder were clarified. The results indicate that the analytical values agree well with the experimental values in the literature and the finite element values. Compared with conventional methods ignoring the influence of curvature, the proposed method improves the calculation accuracy of free torsional shear stress and distortional warping shear stress by 5.0% and 13.8%, respectively. When the ratio of girder horizontal curve radius to girder width (R/B) is less than 10, the bending-torsion coupling effect is significant, while it is negligible when R/B≥70. It is suggested that 10 and 70 be taken as the key thresholds to judge whether the bending-torsion coupling effect is significant or negligible. The eccentric load coefficient of shear stress obtained by the proposed formulas is 1.33, indicating that the eccentric load effect is significant and should be emphasized in design. If the restrained torsion and distortion effects are ignored, the calculated total shear stress of the outer web is conservative, but the average error reaches 3.3%-9.0%, indicating that the effects of both should be included in the refined analysis. The established analytical formulas and obtained laws can provide a theoretical reference for the design and calculation of curved composite steel box girders with corrugated webs.

To develop a method for calculating the shear capacity of corrugated steel webs in bridges, experiments were conducted on three specimens with initial geometric imperfections and nine specimens with longitudinal residual stresses. The actual initial geometric imperfections and the distribution patterns of longitudinal residual stresses of corrugated steel webs were obtained. Based on these results, a finite element model incorporating the actual distribution of initial imperfections was developed and validated. Using the finite element model, extensive numerical calculations and parametric analyses were carried out, and reasonable values for the elastic buckling coefficient of corrugated steel webs in bridges were proposed. Based on the results of nonlinear finite element parametric analysis, a calculation formula for the shear stability capacity of corrugated steel webs for bridges was proposed. The analysis results indicate that the longitudinal residual stresses of corrugated steel webs are symmetrically distributed within one wavelength, with maximum values occurring at the midpoints of the bend segments, inclined plate segments, and flat plate segments, reaching approximately 24.3%-43.4% of the steel yield strength. The initial geometric imperfections of corrugated steel webs exhibit a half-wave sinusoidal distribution along the web height direction, and the amplitudes of the initial geometric imperfections are all less than the acceptance requirement of 1/750 of the web height specified in the code. When calculating the elastic shear buckling strength of corrugated steel webs for bridges, the global buckling coefficient should be taken as 40, and the combined buckling coefficient should be taken as 2. Compared with existing formulas, the proposed formula more accurately calculates the shear capacity of corrugated steel webs under local buckling and combined buckling control, while it is more conservative when applied to corrugated steel webs governed by global buckling.

To establish a calculation method for ultra-low-cycle fatigue (ULCF) cracking of partially concrete-filled steel tube (PCFST) piers and study their ultra-low-cycle fatigue performance, an experimentally validated prediction subroutine was developed for ULCF cracking based on an improved cyclic void growth model (ICVGM). Using this subroutine, high-precision solid element simulations and computational analyses were conducted on nine PCFST piers. The influences of key design parameters, such as concrete filling ratio, slenderness ratio, diameter-to-thickness ratio, and axial compression ratio, on ULCF damage indicators under horizontal reciprocating loads were investigated. Additionally, the relationship between ULCF failure and local buckling failure in PCFST piers was examined in conjunction with the hysteretic behavior of the models. The research results indicate that ULCF failure in PCFST piers generally occurs after local buckling failure. However, different design parameters significantly influence the ductility of PCFST piers, and local buckling deformation leads to more pronounced stress concentrations at deformation locations, thereby accelerating the occurrence of ULCF failure. As the slenderness ratio, diameter-to-thickness ratio, and axial compression ratio increase, the fatigue damage indicators of the pier models at the buckling limit state decrease, and the ULCF problem is not significant. As the concrete filling ratio increases, the fatigue damage indicators of the pier models at the buckling limit state increase, which makes the ULCF problem more pronounced. The diameter-to-thickness ratio and axial compression ratio are two key parameters influencing ULCF cracking, and PCFST piers with good ductility are more likely to experience ULCF failure before local buckling failure occurs. The established finite element model and ICVGM-based subroutine provide a quantitative evaluation method for the ULCF performance of PCFST piers.

This paper aims to investigate the seismic performance of end-bearing prefabricated steel bridge piers with partially filled concrete (PS-PFC). Based on existing research, two large-scale specimens with concrete filling ratios of 0 and 50% were added for quasi-static tests by employing the concrete filling ratio as a parameter. Additionally, finite element simulations and extended parametric analyses of such piers were performed by adopting ABAQUS software. The results show that the common failure mode of the end-bearing PS-PFC in the ultimate state is characterized by the bending deformation of the column base plate and tensile deformation of the anchor rods. Additionally, piers without filled concrete exhibit bulging and tearing of the steel tube above the stiffeners at the column base, indicating that partially filled concrete can effectively suppress local buckling of steel tubes. The hysteresis curves of such piers are relatively full and pinched, indicating good seismic performance. When the filling ratio increases from 0 to 25%, the elastic stiffness and horizontal bearing capacity of piers increase by 9.5% and 17.1%, respectively. Further increasing the filling ratio to 50% produces no significant changes to the specimen's stiffness and bearing capacity. Compared with piers without filled concrete, bridge piers with 25% and 50% filling ratios exhibit an approximately 88% increase in cumulative hysteretic energy dissipation, and demonstrate enhanced resistance to both strength degradation and stiffness degradation. The finite element simulations show good agreement with the experimental results, and the seismic performance of bridge piers improves with the increasing concrete filling ratios. However, when the filling ratio reaches a certain threshold, its further increase has a negligible effect on the horizontal bearing capacity of bridge piers. The proposed theoretical calculation methods for the elastic stiffness, horizontal bearing capacity and optimal concrete filling ratio of end-bearing PS-PFC yield results in good agreement with the test results and finite element simulation results.

To address the strongly nonlinear response of multi-span continuous girder bridges under multi-directional seismic excitation, this paper proposes an endurance time method (ETM)-based approach for assessing the seismic performance of concrete-filled steel tube (CFST) bridge piers. A refined finite element model of a two-span continuous girder bridge is developed using the high-fidelity FE software ABAQUS with solid-shell elements, incorporating a combined hardening-ductile damage model and a triaxial plastic-damage model for confined concrete. The model is validated against bidirectional shaking-table test data to ensure its accuracy. Subsequently, the ETM analysis technique is introduced. Artificially generated multi-component endurance time acceleration functions are employed to simulate the nonlinear dynamic response and damage evolution of CFST piers under different seismic intensities and directions, to quantify the displacement response and damage level of the piers under various scenarios, and to evaluate the applicability and accuracy of conventional combination rules under multi-directional seismic inputs. The results show that the good agreement between the experimental and numerical responses confirms the reliability of the proposed model. Taking the controlling pier P₂ as an example, under multi-directional seismic excitation, its maximum transverse displacement increases from approximately 26 mm to 32-40 mm, corresponding to drift ratios of 3.99%-5.02%, and in some cases exceeds the critical performance limit of 4%. Furthermore, compared with the ETM-based time-history analysis, the traditional square-root-of-sum-of-squares (SRSS) and 100%/30% combination rules conservatively amplify the axial force of pier P₂ from 316.69-320.39 kN to 407.19-440.55 kN under typical bidirectional loading, resulting in an overestimation of approximately 27%-39%. This discrepancy mainly arises from the phase differences among ground-motion components and the nonlinear structural response, which make it difficult for the conventional rules to adequately capture multi-directional coupling effects and the actual dynamic characteristics, thereby compromising the accuracy of seismic performance evaluation. In practical bridge design, it is recommended that the seismic design of critical components be supplemented by time-history analysis that explicitly accounts for ground-motion phase differences and coupling effects. An integrated application of multiple assessment approaches should be adopted to achieve an improved balance between safety and economy.

To investigate the in-plane mechanical behavior of steel tube reinforced concrete (STRC) arch and the composite interaction mechanism of all components, comparative full-range loading tests and refined finite element (FE) analysis were conducted on STRC arch, as well as the corresponding outer reinforced concrete (RC) and inner concrete-filled steel tube (CFST) arches. The failure modes, load-deflection (strain) curves, and crack development of all specimens were tested. The composite interaction mechanism between the outer RC and inner CFST in STRC arches was elucidated. The experiment results show that under a concentrated load applied at the 1/4 span section, four plastic hinges formed at the 1/4 span, 3/4 span, and both arch springing sections, resulting in an anti-symmetric failure. The full-range loading process can be divided into three stages: elastic, cracking development, and failure. The load-deflection curve of the STRC arch is generally consistent with that of the RC arch, and both exhibit similar overall deformation at the ultimate load-bearing capacity. However, the inner CFST remains in the elastic-plastic stage, indicating asynchronous loading. Considering asynchronous and synchronous conditions, the measured load-bearing capacity of the STRC arch is approximately 1.25 and 1.40 times the sum of the capacities of the corresponding RC and CFST arches, respectively, demonstrating a positive composite effect. The FE results show that significant stress redistribution occurs in the section after cracking of the outer concrete, leading to pronounced interaction between the outer RC and inner CFST. The inner CFST effectively restrains crack development in the outer concrete, thereby enhancing both the post-cracking stiffness and ultimate load-bearing capacity. The findings provide a reference for the calculation of load-bearing capacity and the analysis of composite interaction between the outer RC and inner CFST in STRC arches.

To clarify the vehicle operation characteristics, traffic conflicts, and accident occurrence risks in the short spacing interchange weaving areas of ultra-high traffic volume expressways, the Dayouyuan-Songshanhu Interchange of Changping-Humen Expressway was selected as the research object. The vehicle driving data in the short spacing interchange weaving area were collected by unmanned aerial vehicles, and the precise tracking and identification of vehicle operation states were conducted in combination with the Data From Sky Viewer video analysis platform. A total of 1 883 vehicle trajectory data were obtained. From the dimensions of different lanes, the vehicle operation characteristics and diverging and merging vehicle lane-changing behavior characteristics in the short spacing weaving area under ultra-high traffic conditions were deeply analyzed, and the conflict distribution within the weaving area was obtained. The research results indicate that the speed characteristics between lanes present significant differences; the outer lane forms a reverse-trumpet acceleration pattern due to spacing compression (the average speed increases by 12.3%), and the speed bandwidth value at 200 m before its diverging nose surges by 23%; the auxiliary lane achieves efficiency optimization through the "acceleration and deceleration" two-stage strategy; the headway distribution has obvious lane differentiation, and the negative skewness distribution of the main lane is significant (the proportion of 0-80 m spacing is no less than 75%); the proportion of dangerous spacing in the inner lane reaches 61.1%, while the occurrence rate of dangerous spacing in the high-speed area of the auxiliary lane rises to 71.6%; the merging and diverging vehicles present differentiated lane-changing behaviors; the merging vehicles adopt short-distance lane-changing concentrated at 200 m after the nose point, while the diverging vehicles implement long-distance lane-changing, and the conflict severity is higher; the through-merging conflict becomes the main risk source due to the large speed difference. Based on the spatiotemporal dynamic characteristics, it is proposed that the lane-changing length in the diverging area should be no less than 500 m to mitigate the sudden braking risk, and the geometric parameters of the acceleration lane in the merging area should be mainly optimized, to ensure that the vehicle speed matches for safe merging. The theoretical basis and technical support are provided for the safety design of the short spacing weaving area.

Based on toll collection data, this study identified two key parameters affecting accident rates by considering traffic flow composition and the causes of safety risks: traffic flow saturation and the mixing rate of heavy-duty trucks. The algorithm, threshold values, and generation process for each parameter were proposed. The Pearson correlation coefficient method was employed to analyze the independence between the two parameters, and the coefficient of variation was introduced to examine their dispersion relative to the accident rate. By simulating insect feeding characteristics under varying food densities and incorporating polynomial fitting, a safety risk assessment model for mixed traffic flow on expressways was developed. The model was solved using the Taylor series expansion method and iteratively optimized with the Levenberg-Marquardt algorithm. The model's parameters were calibrated using data from 684 expressway sections in Sichuan Province, and its feasibility was verified. The research results indicate that the proposed safety risk assessment model effectively captures the accident rate characteristics of different sections. After 523 iterations, the model achieves a discrete statistical error of 1%, requiring only 1.42 s. The influence of traffic flow saturation and the mixing rate of heavy-duty trucks on the accident rate aligns with the Peal-Reed model and a cubic polynomial model, respectively. The safety risk of mixed traffic flow peaks when traffic flow saturation reaches 33% and the mixing rate of heavy-duty trucks reaches 71%. By incrementally increasing the accident rate by 10.20% within [0.01, 1.03] and subsequently merging groups, it is found that dividing the accident rate into five levels, each represented by a distinct color scheme, can clearly illustrate the safety risk status of the expressway network. Using the 85th and 15th percentiles to define the mixing rate of heavy-duty trucks and traffic flow saturation, respectively, ensures comprehensive coverage of the parameter ranges. The proposed safety risk assessment method holds significant value for dynamically monitoring expressway traffic safety, guiding the allocation of emergency resources, optimizing the deployment of police and road administration personnel, and facilitating evacuation strategies.

The emission and distribution of transportation pollutants are an important basis for transportation system optimization. Given that the actual operating conditions of airports directly affect airport aircraft emissions and that complex interactions exist among various factors, a localized correction model for airport aircraft emissions based on operational simulation was developed to achieve accurate emission quantification. Through the total airspace & airport modeller (TAAM), "multi-scenario-multi-factor" simulation experiments for airport aircraft emissions were conducted to obtain a multivariate dataset of emission parameters including operational time and fuel flow rate. The k-nearest neighbor mutual information algorithm and SHAP model were employed to identify the key factors affecting emissions and to quantify the contribution of each factor to fuel consumption and pollutant emissions. Consequently, a localized emission correction parameter set was constructed. Using historical flight data from Fuzhou Changle International Airport, a case study was conducted and a refined emission inventory was established for aircraft at this airport in 2022. Analysis results indicate that atmospheric temperature, surface wind speed and direction, aircraft approach and departure speeds, air traffic control separation, and weather phenomena are the primary factors influencing airport aircraft emissions. During the taxiing phase, HC and CO represent a substantial proportion of total emissions, accounting for 97.4% and 94.2%, respectively. NO_x and PM_2.5 emissions are predominantly observed during the climb and takeoff phases, and the sums of proportions of the two stages are 52.9% and 66.1%, respectively. As altitude increases, emissions of various pollutants generally exhibit a trend of initially rising, followed by a decline, and ultimately stabilizing. The emission peak of HC, CO, SO₂, and PM_2.5 occurs within the altitude range of 200-350 m, whereas that of NO_x and CO₂ occurs within the 300-500 m range. The relative deviation between the calculated results and those based on selected flight onboard real-time recorded data ranges from 0.6% to 1.3%, whereas the relative deviation from the estimation results derived from the International Civil Aviation Organization (ICAO) baseline emission model estimation results varies from 11% to 23%. The localized correction model for airport aircraft emissions based on operational simulation can provide technical support for assessing the pollution emission effects of airport operations and formulating scientific emission reduction strategies.

To reveal the chain propagation mechanism of natural disasters along railway lines, quantify their threats to railway transportation safety, and analyze the risk evolution laws, a prediction model for natural disaster risk paths along railway lines based on text mining and complex networks was constructed. Based on the historical disaster text dataset along railway lines, the text mining technology was improved; the bag-of-words model was optimized, and combined with the keyword extraction method, core elements such as railway stations, disaster-causing factors, consequences, and severity levels in the disaster data were accurately extracted; based on complex network theory, a heterogeneous network of railway disaster risks was established, with keywords as nodes (3 types of entities) and co-occurrence semantic associations in the same event as edges (6 types of relationships); a multi-path search algorithm was designed to traverse the network topology, and the associated co-occurrence matrix was integrated to quantify the risk transmission intensity between nodes, realizing the procedural mining of multiple types of propagation paths. The analysis results show that the receiver operating characteristic curve of the model is close to the upper left corner; the area under the curve is 0.938; the accuracy reaches 94.873%, and the F1 score is 0.899; the risk transmission values between node pairs are quantitatively output, and high-probability disaster chains are successfully located as: Markam Station → heavy snowfall → Shangri-La Station → personnel disaster → power equipment damage (risk value 0.866), and Jomda Station → Gonjo Station → severe convective weather → casualties (risk value 0.841). The obtained model constructs a disaster semantic network driven by text, which can achieve the quantitative prediction of railway risk paths and the identification of key transmission chains, accurately locate the high-incidence links of secondary disasters, and provide support for the proactive risk prevention and control of railways in complex environments.