Catenary and pantograph are important parts in the power supply system for electrified railways. The dynamic contact between the pantograph and the catenary is pivotal to ensure that the electric locomotives acquire good electricity. Therefore, good dynamic contact between the pantograph and the catenary is a key in the design of the railway power supply system. Given that the contact detection method is common for pantograph catenary contact force at present, and there are few research methods for non-contact detection, a new method based on the image processing algorithm is proposed for detecting pantograph catenary contact force. First, the structure of the pantograph head is simplified, the relationship between the pantograph dynamic contact force and the pantograph head displacement is analyzed, and a new model for calculating the contact force is developed. Next, the ground validation test is conducted on the pantograph-catenary hybrid simulation platform. In tests, the image processing module is used for target tracking and feature extraction of marked points in the collected image. Then, the displacement information is further analyzed by the data processing module to obtain the pantograph head acceleration and other information, and the acceleration signal is corrected. Finally, the contact force results corrected by inertia force and damping force are analyzed. The test results show that the maximum error of the pantograph head displacement detected by image processing is 1.3 mm, showing a high accuracy. Meanwhile, the maximum relative errors of the maximum, average and standard deviation of the dynamic pantograph-catenary contact force are only 5.46%, 5.15% and 4.58%, demonstrating that the measurement error is small. Thus, this method is feasible in detecting the pantograph-catenary contact force and its detection accuracy meets the requirements.

According to the cogeneration characteristics of proton exchange membrane fuel cell and electrolyzer, in order to avoid the waste of heat energy in the hydrogen energy system and further improve the system efficiency, a combined heat–power microgrid system for photovoltaic, wind turbines, fuel cells, batteries, electric boilers, and gas boilers is built by incorporating hydrogen energy system, and a two-stage optimal dispathing method is proposed, including day-ahead scheduling and real-time optimization. The proposed system takes into account the waste heat recovery during the electricity-to-hydrogen conversion, and uses the hydrogen energy system as a thermal-electricity-hydrogen coupling equipment to realize the coordinated utilization and mutual conversion of electricity, heat, and hydrogen energy, and effectively improves the energy utilization rate. In the first stage of scheduling, according to the forecast of the wind-solar power system output and load demand in the day before, the mixed integer linear programming method is used to achieve the day-ahead optimal global schedule with the goal of minimizing the total operation cost of the microgrid. In the second stage of scheduling, based on the results of ultra-short-term predictions, the mixed integer quadratic programming algorithm is embedded in the model predictive control to lessen the economic influence from the prediction errors. Finally, through calculation examples of typical days in winter, summer and transitional seasons, compared with the day-ahead global optimal scheduling, the total cost of the two-stage scheduling method is reduced by 3.24%, 0.76% and 1.66%, respectively, in three types of seasonal days. Through the proposed method are simulated and verified in different scenarios, compared with the basic scenario without energy coupling, in the cases of involving the thermoelectric hydrogen coupling system and thermoelectric coupling system, the total cost and cost of pollution gas treatment with optimal scheduling are reduced by 15.58% and 24.93% respectively. The results show that the proposed method has a real-time and universal quality, which can meet the thermal and electrical load demand in the microgrid, realize stable and independent operation, and improve the system economy and environmental protection.

In order to reduce the impact of electrified railways on the negative sequence of three-phase power grid, and consider energy-saving and economic operation of traction substations, an energy management strategy and capacity allocation scheme is proposed for the co-phase traction power supply and energy storage system in electrified railways. Firstly, with the constraint of the three-phase voltage unbalance limit, the starting threshold of the energy storage device is determined in the cases of the negative sequence exceeding standard. Then the negative-sequence compensation model of the power supply and energy storage system is established to calculate its charging and discharging current. The measured data of traction substations are used to develop the capacity allocation scheme of the energy storage device, which are then validated by the calculation. The results show that the co-phase traction power supply and energy storage system can control the charge and discharge of the energy storage device in real time to realize negative-sequence satisfaction compensation, load peak shaving and valley filling, and regenerative energy utilization. The degree of negative sequence compensation is determined by the discharge power of the energy storage device. The peak-shaving and valley-filling effect and regenerative energy utilization rate are determined by the starting threshold and the capacity of the energy storage device. When the energy storage capacity is constant, the smaller the threshold, the higher the utilization rate of regenerative braking energy.

Power quality issues represented by voltage unbalance and the electrical sectioning issues have severely restricted the safe and efficient operation of the traction power supply system. At present, the ideal solution is the co-phase power supply technology based on symmetrical compensation theory. By integrating the photovoltaic power generation system and the hybrid energy storage system with the DC bus of power flow controller, the utilization of regenerative braking energy, and peak-shaving and valley-filling of traction load can be further achieved to improve photovoltaic penetration rate. For this purpose, the optimal operation model of co-phase traction power supply system is established, which sets the minimum daily operation cost of traction substation as the objective, and takes the charging and discharging strategy of hybrid energy storage, photovoltaic output and power flow controller power as decision variables, and also takes into account the three-phase voltage unbalance constraint. The nonlinear constraints are linearized to formulate the mixed-integer linear programming model, which can be solved by programming solver CPLEX. The case study results show that the integration of photovoltaic and hybrid energy storage can effectively reduce 36.45% of daily operating cost, while the three-phase voltage unbalance meets the upper limit of 2% in the national standard.

Grounding electrode line is an important part of the DC power transmission system, and it is a channel for the unbalanced current and the grounding current in the DC system. When the grounding electrode line is attacked by lightning, the grounding current will form a stable arc in the gap. Since the DC current has no periodic zero crossing point, the DC arc is difficult to extinguish, which damages the line insulation and seriously threatens the safety of the entire system. As the arcing horn of the grounding electrode line is in an open space, and the arc motion is affected by multi-field coupling, a two-dimensional simulation model of the arc horn based on magnetohydrodynamics is built to study the effects of the airflow velocity, direction and the structure of arcing horn on the DC arc motion. The results show that the arc is mainly driven by electromagnetic force and moves along the electrode. Through the arc blowing and stretching, the temperature is reduced, and the voltage is increased, which are beneficial to extinguishing arc. The airflow has a greater influence on the dynamic characteristics of the arc, and the wind speed in the same direction is beneficial to the blowing and dredging of the arc. At the same wind speed, the normal airflow plays a major role in the arc blowing. Electrode types have an important effect on the stretching of the arc. With the same gap distance, the double-horn electrode has a more significant stretching effect on the arc than the single-horn electrode. When the DC ground current is continuously injected, the arc is easy to reignite and difficult to extinguish completely.

To study the vehicle–cargo matching problem regarding the heterogeneous needs of the vehicle owner, cargo owner and platform under the platform mode, the platform demand is introduced given that the previous studies only consider the interests of both vehicle and cargo parties. Firstly, based on the analysis of the participant needs in the vehicle−cargo matching activity, a multi-objective optimization model is built to maximize the satisfaction of the delivery timeliness, minimize the freight cost and maximize the platform revenue. Secondly, in terms of model solution, the non-dominated sorting genetic algorithm Ⅱ (NSGA Ⅱ) with elite retention strategy is improved. On the one hand, elite selection coefficient is introduced in the process of updating the offspring population to improve the diversity of the population, and on the other hand, the adaptive idea is combined to adjust the probability of cross mutation in the algorithm iterations. Finally, the simulation experiments are carried out using the data of vehicles and freights in the areas of Chengdu and Chongqing. The results show that the accuracy of the improved algorithm proposed is more than 91% on small and medium-sized examples, and the average convergence speed is increased by about 45%, compared with the conventional NSGA Ⅱ algorithm. In terms of algorithm stability, the proposed algorithm is less affected by random initialization, and the relative standard deviation of multiple experiments is less than 1%.

Digital twin (DT) is one of the key technologies to promote digitalization and intelligence in the field of rail transit equipment, but its related research is still in its infancy. Focusing on the research and development status of the life cycle of high-speed trains, it systematically analyze the problems of difficulty in closed-loop design, lack of high fidelity, high-precision models, and difficulty in the interaction and integration of cyber-physical data in the process of digital transformation of traditional high-speed train research and development. Combined with the industrial development trend, the new requirements for the life cycle development of high-speed trains are put forward. Then, on this basis, the digital twin technology is introduced and the basic connotation of the digital twin high-speed train is described. The technical framework of the digital twin high-speed train is further described from the two aspects of the construction of the life cycle digital twin model and the functional service of the high-speed train, the key technical problems and challenges faced by digital twin high-speed trains are pointed out. By showing the exploration and application of the deterioration of the service capability of the key components of rail vehicles in the early stage, it is expected to provide a reference for the in-depth research and practice of the digitalization of the full life cycle of high-speed trains in the future.

It is difficult for operators to effectively solve the profitable difficulty caused by the imbalanced distribution of shared vehicles when considering staff-based and customer-based relocation alone. Thus, based on the traditional space-time network, the impact of time-varying road congestion and trip demands on the operation is considered. Based on C# language and O²DES (object-oriented discrete event simulation) framework, an efficient carsharing system model composed of modular station and road segment models is built. Moreover, a simulation-optimization model that jointly determines vehicle inventory thresholds and trip pricing is proposed to maximize the daily net revenue of operators. In order to solve the global optimization problem in a random environment, an elitist genetic algorithm (EGA) with optimal computing budget allocation (OCBA) is designed. Finally, a case study in Chengdu with five sites is conducted to demonstrate the efficiency of the proposed simulation-optimization model. The results show that with the same fleet size, the optimal design can increase the average daily net revenue by 10.37%−162.30% compared with customer-based relocation (fixed pricing); the optimized scheme can increase the profit by 15.34% compared with separate staff-based relocation.

To explore the influence of the uncertainties of traffic systems and travelers’ perception differences on route choice behavior, the bi-objective traffic network equilibrium model is proposed by introducing the network reliability and bounded rationality into travelers’ route choice decision process. To solve multiple solutions of bi-objective user equilibrium model, the Bayesian stochastic user equilibrium model considering travel time reliability and bounded rationality is built, where the Bayesian statistics and bi-level program framework are used to estimate the weight coefficients, and the variational inequality is adopted to build the traffic equilibrium model. The iterative algorithm (IA) and the method of successive average (MSA) are used for the Bayesian estimation model of weight coefficient and variational inequality traffic network equilibrium model, respectively. Case studies show that, the root mean square error (RMSE) of the estimated parameter is decreasing with the increasing of disturbances of observed data and input variable; RMSE reaches to 0.05 after running IA for 15 s, and the convergence accuracy of MSA reaches 10⁻⁶ within 1 s; the variational inequality equilibrium model explores traveler’s risk preference and bounded rational decision process.

In order to investigate the effectiveness of aluminum foam for helicopter crashworthiness design, the mechanical properties of closed cell aluminum foam with two relative densities were tested at quasi-static (0.001 /s) and high strain rates (500 /s, 1000 /s) based on universal testing machine and Hopkinson bar, respectively. An equivalent finite element (FE) model of aluminum foam which considers the strain rate was established. The developed equivalent model of the aluminum foam with different relative densities was applied to the dropping simulation of a helicopter FE model. The crushing level and the deformation of the helicopter were investigated. The results show that the platform stress and mass specific energy absorption increase with relative density and strain rate, but the opposite is true for densification strain. The equivalent finite element model has high accuracy whose response curve can keep consistent with the experimental results. In addition, the maximum deformation of the helicopter floor has been reduced by 28% and 73% and the load-bearing pressure on each component has been reduced by 28% and 42% on average as the aluminum foam with different relative densities was added into the bottom cockpit of the helicopter. The load carrying capacity of aluminum foam with high relative density is higher and more effective.

Aiming at solving problems of distrust in the data interaction between multiple parties and leakage of privacy data, an integrated risk assessment model based on the Cheon-Kim-Kim-Song (CKKS) fully homomorphic encryption scheme is proposed by using homomorphic encryption algorithm in combination with multiple assessment models for risk assessment. Firstly, the triangular fuzzy comprehensive evaluation method is used to determine weights of evaluation indexs, and a variety of evaluation methods are used to process the sample data in the distributed database to obtain the risk evaluation results of related nodes for the same transaction event. Secondly, the public key is used to encrypt the evaluation results, and then homomorphic operation is performed to obtain the encrypted comprehensive evaluation results, so as to avoid data leakage in the process of risk assessment. Thirdly, the private key is used to decode the evaluation results to obtain decrypted comprehensive evaluation results. Finally, 5000 samples from China Railway Express companies are taken as cases to evaluate the risk with eight common evaluation models, including the decision tree model, Adaboost model, Bagging model, ExtraTree model, gradient boosting regression tree (GBDT) model, K-nearest neighbor (KNN) model, random forest model, and support vector machine (SVM) model. In addition, the comprehensive evaluation results encrypted by CKKS scheme are compared with the results directly calculated by plaintext and encrypted by BFV scheme. The findings show that: the integrated risk assessment model is universal and applicable to more common assessment models; the error rates of the comprehensive evaluation results obtained by the integrated risk assessment model are small, within 10⁻⁹ against the actual results; compared with the result encrypted by BFV scheme, the error rate of the result encrypted by CKKS scheme is less than 1/100000 of the former, and the evaluation result is more accurate.

Railway level crossing (RLC) control system is a typical safety-critical system. A novel automatic control system (ACS) that responds to a two-track bi-direction operation is proposed to improve the safety of RLC. Firstly, the operational processes at traditional railway level crossings is analyzed, and the corresponding solutions are proposed in the ACS for three general problems, i.e., clearing inspection, braking distance limitation, and short-time opening of the barriers during continuous work. Secondly, a formal model based on the Event-B language and refinement strategy are developed for the proposed ACS. Finally, proof obligations are checked to verify that the required properties are satisfied, and the Animation is applied to demonstrate the correctness of the system functionality. The results reveal that, compared with the traditional level-crossing management system, the proposed ACS adds the function of two tracks of continuous work, and the use of formal modeling and verification avoids the ambiguity in the system design, all of which have reference significance for RLC safety management.

In order to study the evolution law of oxygen and temperature in the process of spontaneous combustion of loose coal, an experimental system for semi-closed coal fire evolution was built to explore the changes of oxygen concentration and temperature in the process of coal from normal temperature to ignition point, and to establish the natural oxygen absorption intensity model for the spontaneous combustion process of loose coal. The model analyzes the characteristics of oxygen distribution and the horizontal and longitudinal phase movement characteristics of the temperature field during the spontaneous combustion. The results show that the semi-closed coal fire evolution experimental system can better reproduce the natural oxygen absorption process in coal spontaneous combustion, which proves that the natural oxygen absorption effect contributes to the spontaneous combustion of coal mass. During the spontaneous combustion of coal mass, the temperature change time lags behind oxygen concentration change time, and the lag time difference increases with the coal seam depth. The migration trend in the high-temperature area in the horizontal direction is mainly affected by the distribution of cracks and pores at coal body. The natural oxygen absorption intensity and the peak temperature at measuring points decrease with the coal body depth growing, and the oxygen concentration in the lower area without spontaneous combustion is greater than that in the upper layer. The research results provide a theoretical basis for the prevention and control of spontaneous combustion of loose coal under mining, transportation and storage conditions.

In order to study the effect of the quality of shield tail brush on the working performance of shield tail sealing system, based on dynamic compression test and grease escape test, the influence mechanism of long-term extrusion, wear degree of shield tail brush and mortar penetration on sealing performance of shield tail brush are revealed. Firstly, the variation law of the adhesion force of shield tail brush under various influencing factors is discussed based on the dynamic compression test. Secondly, the grease escape volume of shield tail brush under different working conditions is obtained by grease escape test. Finally, taking the adhesion force as the medium, the factors affecting the quality of shield tail brush are connected with the volume of grease escape, and the sealing performance of shield tail brush is discussed. The results show that, long-term extrusion, wear degree of shield tail brush and mortar penetration ratio have significant effects on the elastic properties of shield tail brush, especially the mortar penetration ratio can cause the elastic property loss up to 90%. There is a critical pressure in the grease pressure, and the critical grease pressure with shield tail clearance of 50, 70, 90 mm is 0.4, 0.3, 0.2 MPa respectively. When grease pressure is lower than the critical pressure, the volume of grease escape is very small. When it exceeds the critical pressure, the volume of grease escape increases sharply. The grease pressure further increases by 0.1 MPa, the volume of grease escape increases by more than 4 times. Under the condition of average shield tail clearance (70 mm), the volume of grease escape exceeds the allowable upper limit when the wear of protective plate exceeds 1/2 and the mortar penetration ratio exceeds 10%.

To study the effect of differential subgrade settlement on the potential damage of ballastless track and the dynamic response of high-speed trains, based on the concrete plastic damage theory, a vehicle-ballastless track-subgrade coupling dynamic model that considers the ballastless track bed damage is established. The applicability of the model is demonstrated by comparing with the calculation results of the linear elastic model. The effects of subgrade settlement wavelength, amplitude and the vehicle speed on the dynamic characteristics of high-speed trains are analyzed. The results show that, the differential subgrade settlement could cause the damage to ballatless track bed. The results of the concrete plastic damage model of ballastless track are more in line with actual service status of the track. Among the vehicle dynamics indicators, the vertical acceleration of the vehicle body is most affected by the subgrade settlement amplitude. The vehicle dynamics response is sensitive to the differential subgrade settlement with a wavelength below 20 m, so it should be paid more attention to. The increase of the train speed increases the dynamic response of the vehicle, the wheel-rail force increases significantly, and the vehicle stability index shows a nearly linear growth trend.

This study investigates the typical rail corrugation phenomenon in the braking section of high-speed railways from the viewpoint that the self-excited vibration of wheel-rail friction induces rail corrugation. The corrugation characteristics of a braking section are first mastered and corresponding track irregularities are collected in a field investigation of the Wuhan Guangzhou high-speed railway. Then, from the viewpoint of the rail corrugation induced by the self-excited vibration of the wheel-rail friction, finite element models of the power/trailer wheelset-track-braking system of a high-speed train in the braking section are established. The friction self-excited vibration of the wheel-rail system of the power/trailer is analyzed using the complex eigenvalue method. The possibility of friction self-excited vibrations of the wheel-rail system of the power/trailer is compared under braking and non-braking conditions. The friction self-excited vibrations of the wheel-rail system of the power and trailer under braking conditions are then analyzed. Finally, the effects of the friction coefficient and fastener vertical stiffness on the friction self-excited vibration of the wheel-rail system are studied adopting the control variable method. The comparison between braking and non-braking conditions reveals that the braking condition is more likely to cause the friction self-excited vibrations of the system. Compared with the power/trailer wheel-rail system, the trailer wheel-rail system is more likely to cause the friction self-excited vibration of the system. It is concluded from parametric analysis that when the friction coefficient of the brake device is approximately 0.3 and the vertical stiffness of the fastener is approximately 50 MN·m⁻¹, the possibility of the friction self-excited vibration of the wheel-rail system can be reduced to a certain extent, resulting in the suppression of rail corrugation.

Bridge safety during service is greatly influenced by hydro-abrasion caused by waterborne sand. An independently developed testing device was employed to conduct hydro-abrasion tests on a type of anti-abrasion material, i.e., polyvinyl alcohol (PVA) fiber reinforced cement based composites. Ordinary mortar was selected as the reference material. Firstly, the compressive strengths of the two types of materials were tested and then the weight losses caused by hydro-abrasion were measured. The hydro-abrasion characteristics of the two materials under different impacting angles were analyzed. Finally, the computational fluid dynamics program was used to conduct numerical simulation and the generation mechanisms of abrasion pits were explored on the basis of flow field analysis. Results show that water-binder ratio has the most influence on the anti-abrasion performance; the smaller the water-binder ratio, the larger the material compressive strength and the better the anti-abrasion performance. Abrasion pits on the specimen surfaces have different shapes when suffering impacting of different angles, i.e., the abrasion pit is circular when the impacting angle is 90°, and it is in horseshoe shape when the impacting angle is 30°. The abrasion weight loss of the ordinary mortar specimen and the E3 mix-proportion specimen increases with impacting time. However, the abrasion weight per unit time (5 minutes) of the two types of materials deceases with the increase of the unit time, and their abrasion processes are different.

PLAOD (precise location and orbit determination) is an undifferenced precise GPS data processing software for positioning and orbit determination fully developed by Southwest Jiaotong University. Currently, the software can process GPS observation data, and has the functions of precise positioning, atmospheric inversion and orbit determination for low earth obiter. Following the introduction to basic theory of PLAOD, its performance is focused. Multiple sets of GPS observation data were tested. Compared with the precise product provided by IGS (international GNSS service) and other institutes, PLAOD has shown following features. The static positioning accuracy can reach millimeter level, the kinematic positioning accuracy can reach centimeter level, the estimation precision of the tropospheric zenith delay in static mode is usually better than 1 cm, and the one in kinematic mode is better than 2 cm. There is a high consistence between the ionospheric zenith delay results from PLAOD and the IONEX (ionosphere exchange) product of IGS. In comparison with the reduced dynamic orbit of low earth orbiter provided by JPL (jet propulsion laboratory), the accuracy of orbit determined by geometry method is usually at the centimeter level.

In order to study the influence of the initial crack configuration (such as the initial crack deflection angle and the space position) in asphalt concrete on the change of crack propagation path and growth mode, A crack model with different initial configurations was established by extended finite element XFEM with configuration force at crack tip as fracture criterion to simulate the crack propagation through single aggregate and asymmetric double aggregate. The influence of initial crack configuration on crack propagation was analyzed from the aspects of crack propagation path and crack tip’s configurational force. The results are summarized below: 1) Under single aggregate interference, the crack tip’s configurational force gradually increases with the increase of the angle (the angle between the line connecting the crack tip and the center of the aggregate and the x-axis), indicating that the interference effect of the aggregate on the crack propagation gradually weakens. When the angle is over 60°, the interference effect of aggregate on crack propagation is negligible; 2) Under the interference of asymmetric double aggregate, as the angle (the angle between the line connecting the center of the aggregate and the x-axis) increases, the aggregate interference effect on crack propagation gradually enhances. When the angle is over 45°, the crack tip’s configurational force is significantly smaller, that is, the aggregate exhibits a “crack arresting” effect on the crack propagation; 3) When the initial crack deflection angle changes, the interference effect of single aggregate and asymmetric duel-aggregate on crack propagation is similar. The crack tip’s configuration force increases first and then decreases with the increase of deflection angle ; 4) When it is equal to 45°, the larger crack tip’s configurational force means that the crack tends to be in an unstable state, and the inhibitory effect of the aggregate on crack propagation is weak; hence, the improvement of the crack resistance of the asphalt concrete by the aggregate is limited.

To formulate the train load diagram suitable for the high-speed railway with a speed of 400 km/h, based on the principle of uniformly distributed live load effect of German ICE train, Chinese ZGS and the medium-speed train, 0.65UIC load is proposed as the train load diagram of 400 km/h high-speed railway, referring to the method of determining 0.8UIC load as the train load diagram of high-speed railway in the Provisional Regulations on the Design of Beijing-Shanghai High Speed Railway. Then, for 24 m, 32 m and 40 m span simply supported beam bridges, get the dynamic responses of the train under the action of 400 km/h high-speed train by means of train-bridge coupling vibration analysis method, and the adaptability of dynamic coefficient, vertical deflection, vertical angle of beam end and rail surface irregularity under 0.65UIC load is studied. Finally, the adaptability of the limits of centrifugal force, traction force and braking force to the 400 km/h high-speed railway train is discussed when the 0.65UIC load is used as the design load. The results show that, on the basis of the current code, the 0.65UIC load as the train load diagram of the 400 km/h high-speed railway can be applied to bridge design, and the bridge design index limit and design load limit calculated by this load pattern have a certain safety reserve compared with the response between the operating train and bridges.

The sectional model test in wind tunnels is often used to measure the vortex-induced vibration (VIV) of long-span bridges. Since the sectional model test is based on two-dimensional theory, when the bridge has different aerodynamic configurations along the span due to the partial installation of noise barriers, it is difficult to measure the VIV response directly through the sectional model test. Based on the empirical linear VIV model, an assessment method of VIV between the sectional model and prototype bridge that considers the effects of multiple aerodynamic configurations is proposed. Firstly, the sectional model test is performed on the models with and without barriers respectively. Then, the prototype response of the noise barriers installed and not installed along the span is investigated by ANSYS harmonic analysis, and the corresponding amplitude of the vortex-induced force is obtained. Finally, according to the actual installation position of the noise barrier along the span, the vortex-induced force is imposed on the bridge and the prototype response with the partially installed noise barrier is obtained. In addition, based on the method in this paper, various noise barrier installation schemes are numerically simulated. The results indicate that fully enclosed noise barrier will significantly reduce the aerodynamic performance of the main girder and the overall VIV will be affected by partial installation of barrier to a large degree. The method in this paper can estimate the prototype response of multi-aerodynamic configurations bridges through the results of sectional model tests. The installation of the noise barrier should be arranged on the side span as far as possible under the conditions of noise reduction. If the arrangement length exceeds the position of the bridge tower, it should be shortened as much as possible to reduce the vortex-induced response.

In order to study the driver’s sight line under vertical vortex-induced vibration (VVIV) of long span suspension bridges, a numerical framework of coupled wind-vehicle-bridge system considering VVIV (termed as WVB-VIWW) is proposed by introducing a vortex aerodynamic model into the traditional coupled WVB theory. Based on the proposed framework and with the aid of geometric construction method, the equation of driver’s blind region under VIVV is derived based on a vortex vibration mode with three half-sine-waves. Subsequently, the proposed WVB-VIVV framework and equation of driver’s blind region are applied to a long span suspension bridge which has experienced VVIV. The influence of several key factors, i.e., vehicle type, vehicle speed, and the time instant where vehicle enters the bridge, on the maximum height of driver’s blind region, the total time duration of the driver’s blind region, and the ratio of driver’s blind region is investigated. The results indicate that the maximum height of the driver’s blind region varies periodically, and the period is approximately equal to the time required by the vehicle to travel through a half-sine-wave. The vehicle speed has an insignificant effect on the maximum height of driver’s blind region. Because the driver’s sight line height varies with the vehicle type, the lower the driver’s sight line height, the higher the maximum height of the driver’s blind region. Additionally, the vehicle weight could increase the maximum height of the driver’s blind region by increasing the overall deflection of the bridge span. It is also found that the total time duration of driver’s blind region is insensitive to the time instant where vehicle enters the bridge, but the total time duration of driver’s blind region decreases with the increase of the vehicle speed. Furthermore, the time instant where the vehicle enters or the vehicle speed has barely no effect on the ratio of driver’s blind region. However, the vehicle type has remarkable influence on the ratio of driver’s blind region, e.g., the ratio of driver’s blind region for sedan car and megabus is approximately 21% and 12%, respectively.

The mechanical analysis of shallow noncircular tunnels is of great significance to the construction safety of urban subway tunnels. The difficulty in solving this problem originates from the influence of gravity and the determination of conformal mapping. To this end, a decoupling conformal mapping method with the framework of complex variable theory was proposed. In this method, the analytic function was decomposed into two groups of sub-functions, which were expressed in different local coordinate systems. These two sub-functions can exactly express the mechanical field of the computational domains inside the ground surface and outside the tunnel boundary. Then the ground and tunnel boundaries can be mapped independently by conformal transformation. Furthermore, the boundary condition equation used to determine the analytic function was transformed into the frequency equation using the fast Fourier transform method. Finally, the proposed method is applied to the analysis of ground settlement caused by the shallow tunnel excavation. From the results, the following conclusions can be drawn: 1) The tunnel shape has a significant effect on the ground settlement, and its main factor is the height-to-span ratio. 2) The buried depth affects both the ground settlement and the width of the settlement trough. Its sensitivity increases with the decrease of buried depth. 3) The lateral pressure coefficient has little effect on the width of the ground settlement trough. 4) Compared with the finite element method, the proposed method can obtain high-precision results at a small computational cost.

Soilbags have been successfully applied to the reinforcement of building foundation with obvious effect on seismic isolation, but their deformation characteristics under dynamic load have not been studied in depth yet. In order to further analyze the vertical bearing capacity and deformation characteristics of soilbags, a series of laboratory unconfined ultimate loading tests and cyclic compression tests were conducted, and the effect of the number of loading cycles, the static load, and the cyclic load ratio on the dynamic characteristics of soilbags was studied in terms of the vertical stress-strain variation and the dynamic compression modulus. The test results show that with the increase of the number of layers, the ultimate strength of stacked soilbags decreased gradually and tended to a stable value of 0.7 MPa, and the peak compression modulus also decreased and stabilized at 6.73 MPa. An obvious plastic deformation of stacked soilbags was observed at the beginning of the cyclic compression test, and the vertical residual strain generated in each cycle decreased gradually and tended to zero with the increase of the number of cycles. The dynamic compression modulus was basically stable throughout the whole testing process, and was not affected by the number of cyclic loads. With the increase of the upper static load, the dynamic compression modulus of the stacked soilbags increased gradually. After 200 cycles of loading, the dynamic compression modulus of soilbags with the static load of 50 kN reached 53.87 MPa. However, it significantly decreased with the increased cyclic load ratio. When the cyclic load ratio was 0.4, the dynamic compression modulus of soilbags could still reached 49.39 MPa after 200 cycles of loading. In general, under the action of vertical dynamic load, the soilbags can satisfy the requirements of bearing capacity and stability as a kind of seismic isolation material.

high-speed railway is characterized by fast operation speed and high smoothness, and has certain advantages when used as a platform for train launching. Its vibration acceleration can be used as a critical parameter to assess the structural damage in high-speed railway subgrade. Using the finite element analysis software ANSYS, a semi-infinite ballastless track-subgrade-foundation nonlinear coupling static analysis model is established by elastic-plastic theory and introducing the three-dimensional uniform viscoelastic artificial boundary with its boundary element. The modal shape and natural frequency of the model system are obtained by modal analysis, and then a dynamic analysis model is established. The dynamic model is verified by comparing with the beam-slab model on an elastic foundation. Based on the dynamic analysis model, the time-domain acceleration signals of each structural layer under ejection impact load are obtained. Finally, the acceleration signals are analyzed through EEMD-HHT transform. The results show that the peak instantaneous acceleration occurs at the time of sudden change of load, and the amplitude of acceleration is obtained at 0.17 s. The acceleration components of each structural layer are mainly distributed in the range of 0–20 Hz, and there are two prominent peaks at 2 Hz and 10 Hz, most concentrated in the vicinity of 2 Hz. The three structural layers including the self-compacting concrete layer, the pedestal plate and the subgrade surface layer almost do not absorb any vibration acceleration components, but the subgrade bottom layer and the zone below it have significant absorption. Therefore, more attention should be paid to the dynamic response of the subgrade surface layer and upper layers in the ultra-low frequency range of 0–20 Hz

In order to study the effects of various plane forms on the mechanical performance and stiffness degradation of diagrid outer tube structures, the numerical model of a regular octagonal diagrid structure is verified by the hor-izontal pushover test. Diagrid structures with plane forms of quadrilateral, hexagon, octagon, dodecagon, and icosikaitera (24-gon) are further established. Compared with the quadrilateral framed tube structure model, the effects of plane forms on the lateral stiffness, ductility, internal force, shear lag and yield order are analyzed. Results show that the distribution range of ductility coefficient of various plane diagrid structure models is 4.27–5.22. With the number of plane edges increasing, the overall lateral stiffness increases gradually, and the better the ductility, the more reasonable the stress mechanism. In addition, since the axial force is mainly transmitted through tilted columns in diagrid structures, the shear lag effect of diagrid structures is obviously smaller than that of the frame tube structure. With the increase of the number of plane edges, the shear lag ratio of the compression flange of the diagrid structures decreases from 1.32 to 0.82. The shear lag ratio of diagrid structures with plane forms of regular hexagon, regular octagon, regular dodecagon and regular 24-gon is closer to 1.00 than that with the plane form of regular quadrilateral. In the horizontal pushover test of diagrid structures, the yield first occurred to the tilted column in the intersection area between the flange and the web with increased plastic deformation, then extended to the flange and the middle of web, and finally extended upward from the structure bottom.

In order to characterize and assess the interfacial bonding strength of steel structure coatings under wind-sand erosion, expressions for calculating interfacial stresses of the steel structure coating under wind-sand erosion are established using theories of contact mechanics and interface mechanics, based on the typical sandstorm background of Northwest China. The interface crack initiation position of steel structure coating is determined by combined use of the fracture mechanics theory and finite element analysis method. The interfacial stress failure criterion considering the influence of compressive stress is established at the crack position. The results show that when the erosion angle is 30° and 60°, the maximum interfacial shear stress is located at 200 mm and 180 mm in front of the erosion point, and the maximum interfacial compressive stress is located at 100 mm and 50 mm in front of the erosion point, respectively. The interface crack in the coating initiates at the position of the maximum interfacial shear stress. In addition, the proposed interfacial stress failure criterion for coatings under wind-sand erosion is similar to the Mohr-Coulomb strength criterion. The slope depends on the erosion angle of the sand particles. When the erosion angle is 30° and 60°, the slope magnitude is −0.599 and −0.467, respectively.

Recycled concrete aggregates are used to replace the gravel core material of encased stone columns, forming a new foundation treatment method—recycled concrete aggregate encased column, to improve the problem that the gravel strength cannot be fully exerted when the encased stone column is used to treat liquefied and soft soil foundations. Laboratory model tests were performed to study the effect of encasement length, stiffness, and the ratio of column length to diameter on the bearing characteristics and aggregate fragmentation degree of the encased recycled concrete aggregate column. The results show that when the length of encasement is 1 to 6 times the column diameter, the bearing capacity of the column can be significantly increased by increasing the encasement length. When the length of encasement is less than 1 or more than 6 times the column diameter, the length change of encasement does not significantly influence the bearing capacity of the column. The critical stiffness of encasement is about 100 kN/m. When the stiffness of the encasement is less than the critical stiffness, increasing the encasement stiffness can prominently improve the bearing capacity of the column. However, when the stiffness of the encasement is greater than the critical stiffness value, increasing the encasement stiffness cannot significantly improve the bearing capacity of the column. When the length of the geosynthetic-encased recycled concrete aggregate column is fixed, columns with a length-to-diameter ratio greater than 10 have a lower bearing capacity, and mainly produce local bending to varying degrees within the depth range from 10 cm to 30 cm, while columns with a length-to-diameter ratio less than 7 have a relatively higher bearing capacity and mainly experience slight bulging deformation without local bending. Besides, there is a positive correlation between the fragmentation degree of the recycled concrete aggregate and the ultimate load that the column can withstand. Increasing the encasement length, stiffness and column diameter will increase the fragmentation degree of the core material. Therefore, when designing a single geosynthetic-encased recycled concrete aggregate column, full consideration should be given to the relationship between the encasement length, stiffness, the ratio of column length to diameter, and the fragmentation degree of the concrete aggregate, to obtain the optimal design scheme.