At present, the research on the arching problem of steel truss bridges in engineering mainly focuses on the N-type truss sections, but there is no unified calculation method for the pre-camber setting of K-type steel truss bridge sections. In order to solve the problem of arching in K-type sections, the mathematical expression for the expansion and contraction of each member was derived, which was based on the mechanical equilibrium equation of a structure formed in stages and took the relative pre-camber of the sections as an input. Aiming at the characteristics of the pre-camber setting of the through type steel truss girder bridges, the formulas for the expansion and contraction of the members were further obtained for three cases: simultaneous expansion and contraction of the lower diagonal web members and vertical web members, simultaneous expansion and contraction of the lower diagonal web members and upper chord members, and simultaneous expansion and contraction of the upper chord members and upper and lower diagonal web members. With the help of real bridge data calculation and geometric trial calculation, the proposed method was verified. The research results show that the proposed method is practical and feasible, which fully verifies that the unstressed arching of K-type steel truss bridge sections is an absolutely geometrical arching, and the arching process will not generate additional internal forces or reaction forces from the arching support.

Current studies on the crest bond shear connector (CR) in steel-concrete composite bridges mainly focus on the bearing capacity. Yet, few works have been done on the shear stiffness of the connector and there is no universal theoretical formula to describe the shear behavior. Therefore, experimental studies were conducted to establish a reasonable formula to calculate the shear stiffness of CR connectors, and the corresponding finite element model was then established and verified based on the experimental results. The load-displacement curves of shear connectors with different structural parameters in the elastic phase were simulated, and the variation law of elastic shear stiffness of connectors under different parameters was revealed. The equivalent spring model and equivalent rod spring model were adopted to investigate the shear stiffness of shear members, concrete tenons and steel bars penetrating through concrete tenons, respectively. The theoretical formula to calculate the elastic shear stiffness of the CR connector was derived based on the superposition relationship of stiffness in the elastic stage. The comparison between theoretical calculation and finite element fitting results shows that the error between the theoretical calculation value and the fitting value of the elastic shear stiffness of the connector is within 7.7% and the results show good consistency, which can be used as a basis for structural design.

To study the permeation and diffusion behavior of snow-melting agent ions in asphalt, six kinds of snow-melting agents, including A3N (prepared from acetate, NaNO2 and urea), Ca (CH3COO)2, Mg(CH3COO)2, KCH3COO, NaCl, and NaNO2, were employed to conduct penetration experiments on asphalt. The influence of snow-melting agents on viscosity, plasticity and high-temperature stability of asphalt were investigated through changes of three major indicators. An ion chromatograph was used to detect changes of ion concentration in snow-melting agent solution and analyze the permeation and diffusion patterns of cation and anion of snow-melting agents. Based on the changes of the concentration of cations and anions of snow-melting agents during each soaking cycle, Fick's law was introduced to analyze the permeation and diffusion behavior of snow-melting agent ions in asphalt. The results show that the viscosity and plasticity of the base asphalt and SBS-modified asphalt increase after soaking with the snow-melting agent, and NaCl has the greatest impact on viscosity and plasticity. Acetate and A3N can reduce the high-temperature stability of asphalt, while NaNO2 and NaCl can improve the high-temperature stability of asphalt. The permeability of snow-melting agent ions in the base asphalt is stronger than that of the SBS-modified asphalt. The maximum diffusion intensities of cations and anions are K+ in KCH3COO and CH3COO- in Mg(CH3COO)2. After 5 cycles of permeation, the concentration of K+ in the snow-melting agent solution above the base asphalt and SBS-modified asphalt is decreased by 27.59% and 16.89%, respectively, while the concentration of CH3COO- is decreased by 35.16% and 19.38%, respectively. The Fick's law diffusion model can better describe the changes in the adsorption capacity of various ions by asphalt, among which the non-linear fitting goodness of cation adsorption capacity is higher than that of anion, making it easier to be quantified and analyzed.

A systematic study was conducted to explore the mechanism of pile-anchor supporting for high slopes of highway road cuttings, taking the landslide treatment of a road cutting slope in Dengjia Village, Yunnan Province as an example. Through on-site geological survey and multivariate data analysis, the engineering geological conditions and causes of the landslide were identified. FLAC3D numerical simulation was used to study the stability of the high slope without support, and two schemes of retaining walls and pile-anchor supporting were compared and analyzed. Taking a scheme with the prestress being 400 kN, the pile spacing being 4m and the pile diameter being 1m as a basic one, the influence rule of pile-anchor parameters on the stress performance of pile-anchors and slope safety factors in high slopes of road cuttings was analyzed through single factor analysis method. The research results show that, although the retaining wall can effectively prevent slip at the bottom of the slope, its stability effect on the middle and upper parts of the slope is not good. The pile-anchor supporting structure has a good reinforcement effect on the whole landslide body. The displacement of the pile exhibits a characteristic of "being large in the upper part and approaching 0 in the lower part", whose shear force and bending moments have multiple extreme points, and most of them appear above the sliding surface. With the increase of pile diameter or the decrease of pile spacing, the safety factor of slope increases. On the other hand, the prestress of anchor cable has little effect on the safety factor of slope.

Based on the particle flow computational framework, the Weibull distribution was employed to construct a heterogeneous numerical model of rock mechanics with a single pre-fabricated crack, and uniaxial compression tests of heterogeneous rock was simulated. The influence of the pre-fabricated crack inclination angle θ on the stress-strain response characteristics, microcrack behavior and failure mode of rock numerical specimens was analyzed. The results indicate that the peak strength (σpeak) increases with the increase of the homogeneity of rock (m) and finally tends to be stable. However, due to the influence of θ, σpeak shows a small drop, with a maximum value of 7 MPa. The failure surface of numerical samples of heterogeneous rocks is mainly composed of microscopic tensile cracks. The macroscopic failure modes of heterogeneous rocks can be divided into “inverse diagonal type”, “semi-dual type”, “coupling type” and “diagonal type”.

The level of integrated transport development has an important supporting role for the regional economy. In order to accurately assess the level of integrated transport development of a region, a three-tier evaluation index system containing 4 secondary indicators and 30 tertiary indicators was constructed by taking into account various influencing factors. And in order to reduce subjective influence, the cloud model was used to improve the analytic hierarchy process method to calculate the weights of evaluation indicators, and the TOPSIS evaluation model was combined to calculate the distance between each indicator of the evaluation object and the optimal indicator, in order to obtain the ranking of the integrated transport development level of each evaluation object. Taking the Yangtze River Delta (YRD) region of China as a case study, its integrated transport development level was evaluated by the proposed model. The results show that: in the YRD region, Jiangsu Province ranks first in terms of its high level of integrated transport development, Shanghai ranks second slightly higher than Zhejiang Province, Zhejiang Province ranks third with a lower score, and Anhui Province ranks the lowest. According to the calculation results and scores of various indicators, the Yangtze River Delta should combine with the actual situation of each province and city to make up for the shortcomings of the transport to achieve high-quality transport integration.

Faced with the rapid growth of air passenger and cargo transportation services and the sharp increase in congestion at various airports during peak departure hours, it is necessary to optimize the configuration of departure flights, reduce the total departure delay time during peak hours, and ensure the total deviation of flight schedules applied by airlines. A dual objective departure flight schedule optimization model was established, considering factors such as flight schedule uniqueness, corridor flow limitations and airport capacity limitations. The whale optimization algorithm (WOA) was improved and solved by elite reverse strategy and golden sine algorithm. Taking Beijing Capital International Airport as an example, AirTOp was used to simulate and verify the optimized results. The results show that the average flight delay is decreased by 77.62% after optimization. Therefore, improving the whale optimization algorithm can effectively reduce delays during peak departure hours, enhance airport operational efficiency, and reasonably allocate limited time resources.

To enhance the operational efficiency of container terminals, the continuous berth allocation problem considering tidal factors and berth preferences was studied. A mixed-integer linear programming model was established with the objectives of minimizing ship waiting, delayed departure, berth deviation, as well as minimizing fuel consumption costs during the port period, by introducing non-overlapping ship spatiotemporal rectangles and tidal time window constraints. According to model features, CPLEX solving software, fish swarm algorithm, cuckoo search algorithm, and the hybrid cuckoo search-fish swarm algorithm were used for solution. The arrival data of 20 ships of different sizes with a planning cycle of 36 hours was utilized as a case study. A berth allocation plan that met the requirements of tidal time window and berth preference was obtained by solving the case study. The solution for the case study shows that for smaller instances, CPLEX can find the optimal berth allocation scheme in a relatively short time. However, for larger instances, CPLEX requires longer time for solution, while the cuckoo-fish swarm hybrid algorithm can obtain suboptimal solutions with a difference from 0.39% to 4.2% from CPLEX within an average of 3 minutes. Comparison between different algorithms demonstrates that the hybrid cuckoo search-fish swarm algorithm has better solving ability. In the berth allocation scheme obtained by the proposed hybrid algorithm, the entry and exit times of tidal vessels are all during high tide periods, and more than 85% of vessels receive loading and unloading services within 200 meters of their preferred berthing points.

To improve the utilization rate of green light time of signalized intersections in the connected environment, a coordinated optimization control method for speed and signal timing of connected vehicles at single point signalized intersections was proposed, which was according to the interactive information such as vehicle speed, location, and signal status between connected vehicles and traffic facilities. The proposed method used the fleet discrete theory to predict the arrival rate of vehicles at intersections and then optimized the intersection signal timing according to the predicted results. On this basis, minimizing the total number of queued vehicles within the cycle was taken as the optimization goal. The speed of each connected vehicle passing through the intersection was judged, and the optimal driving speed of the connected vehicle was solved according to the vehicle numbering order, achieving effective coordination between speed guidance and intersection signal control. MATLAB software was used to simulate and analyze the proposed model. Research results show that after the collaborative optimization of signal optimization and speed guidance, the proposed speed guidance and signal collaborative control method can increase the number of vehicles passing through the intersection at the same time, reduce vehicle delays, and effectively improve the traffic efficiency of the intersection.

In the context of predictable disasters, how to efficiently organize the safe evacuation of evacuees in the disaster affected area and reasonably allocate materials is the core link in emergency evacuation activities. Therefore, the overall optimization strategy for the coordinated operation of emergency evacuation and material allocation in a multi-level emergency service network was studied. Firstly, the evacuated people walked to temporary resettlement sites and were then evacuated by emergency vehicles to shelters. Then, the emergency material allocation center transported the materials to the shelters. Finally, the various economic costs and benefit costs of the people involved in the above process were analyzed. A dynamic integer programming model was established with the goal of minimizing the total system cost, focusing on the collaborative cooperation between evacuation and material allocation in continuous multi-period dynamic emergency activities. By programming on the GAMS platform and applying the CPLEX solver, the effectiveness of the proposed model was verified through experimental road networks of different scales, and sensitivity analysis on key parameters was conducted. The research results indicate that there is a mutual influence between the dynamic evacuation plan and the amount of allocated emergency supplies. Sufficient supplies can avoid looting, but it is necessary to consider the balance between disaster victims and emergency supplies in the limited space of the shelter. Improving the response rate of evacuees and increasing the capacity of shelters are helpful to achieve a more ideal "zero detention" evacuation state. Determining a reasonable unit penalty cost for unevacuated crowds can effectively ensure a high evacuation clearance rate, while can also control the system penalty cost from being unnecessarily high.

To improve the prediction accuracy and generalization ability of the number of trains operating on the Xian China Railway Express, a prediction method of train number in operation based on the SARIMA-RF combination model was proposed, comprehensively taking into account the linear and nonlinear characteristics of the time series data of the Xian China Railway Express. Firstly, the seasonal autoregressive moving average (SARIMA) model was used to predict the number of vehicles in operation. Secondly, the random forest (RF) model was used to correct the residuals and construct a combination model. Finally, the combination model was compared with ARIMA, SARIMA, RF and XGBoost. The monthly operating data of the Xian China Railway Express from 2014 to 2023 was used to carry out the experiment. The experiment predicts that the number of vehicles operating in 2024 will be 244000 and 267100 in 2025. The comparison results show that the MSE, RMSE, MAE, and MAPE of the combination model are 0.0037%, 0.0610%, 0.0530%, and 3.41%, respectively, which are higher in accuracy than other models.

In order to reduce highway traffic congestion and accident casualties and property losses, it is necessary to improve the accuracy and applicability of accident duration prediction results. Based on the data of 1 362 highway traffic accidents, 16 factors affecting the duration of highway traffic accidents were selected as characteristic variables. After statistical analysis of continuous characteristic variables and assignment of discrete characteristic variables, a prediction model for the duration of highway traffic accidents based on SO-BiLSTM was constructed. The research results show that the mean values of average traffic flow, average vehicle speed, and speed deviation are the smallest within the roadway sections with accident durations greater than 120 min, which are 27 882 pcu/h, 90.4 km/h, and 18.0 km/h, respectively, and the mean value of the large vehicle mixing rate is the smallest within the roadway sections with accident durations of less than 30 min, which is 34.0%. The average age of the perpetrators with an accident duration of ［60, 90) min is the largest, which is 45 years old. The average driving experience of the perpetrator with an accident duration greater than 120 minutes is the highest, which is 91 months. The number of iterations and the population size of the proposed SO-BiLSTM model are set to 40 and 30 as the optimal. The MAPE value for predicting the duration of corresponding accidents is 8.9%, which is 1.7% to 7.6% lower than PSO Elman, BiLSTM CNN, GA-BP, and LSTM, and improves the accuracy of the prediction result for accident durations more than 120 minutes. The research results are helpful to formulate highway traffic accident relief control and emergency rescue measures and improve the level of highway traffic safety management.

Based on the fire evacuation theory, the available safe evacuation time (tASET) model and the required safe evacuation time (tRSET) model were established to investigate the evacuation time at key locations such as staircase, escalator entrances and station exits after a fire occurred in four types of spatial structures in subway stations (open structure, wall structure, staircase structure, and wall + staircase structure), respectively. Pyrosim was used to simulate the fire development and Pathfinder was used to simulate the evacuation condition. A comparative analysis of tASET and tRSET at critical locations under four kinds of spatial structures was conducted to assess the safety of different ignition locations. The results of the study show that tASET is mainly determined by the time for visibility to reach criticality; tRSET is mainly based on the evacuation condition of building escalators and exits. Among the four selected locations, only the open structure can safely evacuate personnel in the event of a fire; the wall structure is not conducive to the safe evacuation of personnel at the building escalator exits after a fire; and after a fire occurs in the staircase structure and the wall + staircase structure, they are both in a hazardous condition, resulting in the inability to evacuate personnel safely.

Reasonable use of wake surfing technology during formation flight will lead to significant lift enhancement performance for the rear aircraft. Based on this principle, a formation consisting of two fixed wing unmanned aerial vehicles was designed according to the "V" shape formed by migratory birds during flight. CFD was used to draw overset grids between the unmanned aerial vehicles and the fluid domain, numerical simulation was conducted on flight formation, and the aerodynamic parameters of the flight formation were analyzed. Research results show that under aerodynamic action, the wake surfing effect has a minimal impact on the front aircraft and a significant impact on the rear aircraft. The longitudinal and vertical spacing of the twin aircrafts affect the lift coefficient, drag coefficient, lift drag ratio, pitch torque and other parameters of the rear aircraft. At the appropriate position and angle of attack, the lift coefficient of the rear aircraft can be increased by 11.7%.

In order to further clarify the ultimate load-bearing capacity of the hull structure, it is necessary to comprehensively consider the effects of initial welding defects, the Bauschinger effect of the material and the properties of the cyclic loading on the ultimate strength of hull stiffened plates. The thermal elastic-plastic finite element method was used to simulate the welding process of the flat-bar stiffened plate, and then the ultimate strength of the stiffened plate reaching the elastic shakedown state under cyclic compression-tension loading was analyzed. The research results show that the welding residual stress of the hull stiffened plate is most significantly released after the first cyclic unloading and is increased with the increase of the cyclic load amplitude. Under cyclic loading, the ultimate strength of the hull stiffened plate is increased after reaching the elastic shakedown state, but the cyclic load amplitude does not have a significant effect on the improvement of ultimate strength. Under the same cyclic load amplitude, the ultimate strength calculated by Chaboche model is slightly higher than that by the ideal elastoplastic model. The thermal elastic-plastic finite element method can be used to directly obtain the initial welding defects of hull stiffened plate, which has a certain reference value for the further study of the ultimate load-bearing capacity of the hull structure under cyclic loading.

As the main load-bearing component of a train, the fatigue strength of the body of a straddle monorail vehicle plays a crucial role in the safe operation of the train. In order to improve the accuracy of fatigue analysis of monorail vehicle body and simulate the fatigue damage of the vehicle body in the operation practice of monorail vehicle, the flexible treatment was carried out on the monorail vehicle body. The rigid flexible coupling dynamics model of a straddle type vehicle containing a flexible body was established. The virtual iteration method was used to apply white noise as the initial input excitation at the characteristic parts of the vehicle, and the measured acceleration of the straddle type monorail vehicle line was taken as the target signal. Then the simulation response spectrum of the vehicle model and the experimentally measured response spectrum were systematically identified and iteratively iterated to obtain the excitation spectrum at the connection position between the vehicle body and other components. Based on the virtual iterative excitation spectrum, the high-precision load spectrum was obtained. According to the linear fatigue damage theory, fatigue damage and life analysis were carried out on the body of the straddle type monorail vehicle, and an improvement plan for the vehicle body structure was proposed. The analysis results show that the fatigue simulation results have good consistency with the actual damage location of the vehicle body, which verifies the highprecision of the fatigue analysis results of the vehicle body load spectrum obtained by the virtual iteration method. The structural improvement plan has increased the service life of the vehicle body structure improvement position by 191%.