Liquid metal takes into account the characteristics of both liquid and metal, and it is increasingly studied and applied in various fields of engineering. Gallium-based liquid metal is liquid at room temperature, with a high boiling point, high electrical conductivity, high thermal conductivity, safety, non-toxicity, and other excellent characteristics, and it has been widely used in many fields such as electricity, heat, mechanics, and biomedicine. At present, gallium-based liquid metals have become a frontier research hotspot. By comprehensively comparing the research status in China and abroad, the preparation methods and performance improvement measures of gallium-based liquid metals were introduced, and the physical and chemical properties of several typical gallium-based liquid metals were analyzed. The functional principles and research progress of gallium-based liquid metals in the fields of power equipment, flexible electronics, power storage, heat dissipation cooling, current-carrying friction, and extreme pressure lubrication were summarized, and its future research focus was put forward. Based on the characteristics of gallium-based liquid metals, their potential applications in material modification, new electronic devices, solar cells, rail transit, electromagnetic ejection, and other fields were analyzed and prospected.

Aiming at wind and light abandonment and economic cost optimization in regional integrated energy systems, an optimal scheduling method of regional integrated energy systems considering power to gas (P2G) two-stage model is proposed. First, the regional integrated energy system with electricity-gas-heat-storage-hydrogen coupling is regarded as the research object, and the equipment models and two-stage P2G models of the system are established. Secondly, the optimal scheduling model of the system is established under the relevant power constraints. On this basis, the incentive response from power demand side is introduced, and the load curve is optimized with the mixed integer programming YALMIP function. The system economy is improved by changing the power consumption time of the transferable load. Finally, the mixed integer linear programming method is used to solve the optimal scheduling solution and the costs under the objective of minimizing the daily operation cost. According to the historical data of a certain area, the presented optimization scheduling method is adopted to obtain optimization scheduling results for the integrated energy systems in this electricity-gas-heat-storage-hydrogen coupling area, and the rationality and effectiveness of this method are verified by technical and economic analysis in terms of different seasons, P2G stages and demand side response. The results show that after under the two-stage P2G, the amount of abandoned wind and light is greatly reduced in winter and summer, and the economic cost is reduced by 32.62% and 61.64%, respectively; when introducing the demand side response, the proportion of system economic cost reduction in winter is further increased to 33.69%.

As suburban railways necessitate uninterrupted power supply, bilateral power supply technology is explored to apply in canceling electric phase separation. The equivalent circuit models of parallel bilateral power supply and tree bilateral power supply are established in different modes of external power supply. The calculation model of equilibrium currents is deduced, and the measures are analyzed to reduce equilibrium currents. Taking a city line as an example, the power flow distribution and equilibrium current are simulated under different system operation modes, and the calculation model of equilibrium currents is verified. The feasibility analysis is conducted as to using the bilateral power supply modes in the single-phase AC traction for suburban railways. The results show that in this case when the municipal lines are closed, the maximum power of the traction transformer is 70.36 MV·A, the maximum voltage fluctuation 0.7025%, and the maximum current in 110 kV transmission line 833.418 A. In the bilateral power supply system, the traction transformer and the transmission line can endure the influence of the electromagnetic loop network on the power flow distribution of the grid, which meets the power system requirements in the steady state. The proportion of the equilibrium current in loop closing lines is 2.322%, which has small influence on the system.

The tree continuous co-phase power supply system of heavy-haul railways can minimize the safety hazards caused by neutral sections in the line and improve the utilization rate of regenerative braking energy, power supply capacity, and power quality of the traction power supply system. In order to make the tree continuous co-phase power supply system run smoothly, the operation status of the system was studied from four aspects: equalizing current, power supply capacity, negative sequence evaluation, fault analysis, and protection configuration. The equalizing current evaluation model of the bilateral power supply system under different topologies was constructed to reveal the external power supply composition of the tree continuous co-phase power supply system of heavy-haul railways. With the tree continuous co-phase power supply transformation scheme of a heavy-haul railway as an example, the power supply capacity of the system under normal and fault conditions and the negative sequence impact on the external power grid were explored. Different types of faults in the system were analyzed, and the protection configuration scheme of the system was proposed. Compared with parallel bilateral power supply, the results show that the tree continuous co-phase power supply system will not produce an equalizing current when the transformer ratios of two adjacent traction substations are the same. The minimum voltage of the up and down traction network of the transformation scheme is 22.74 kV, which meets the voltage requirements of the traction network. By setting the combined co-phase power supply device, the 95% probability value and maximum value of the three-phase voltage unbalance factor of the system are 1.20% and 1.65%, respectively. Compared with the traditional protection device scheme, the proposed protection configuration scheme can ensure the minimum outage interval of the traction network.

The single-inductor dual-output (SIDO) Buck LED driver has two output branches, namely LED₁ and LED₂. Between these two output branches, there is cross regulation. In order to reduce the output cross regulation of a SIDO Buck LED driver operating in continuous conduction mode (CCM) of the inductive current, the current-current (I²)-controlled SIDO Buck LED driver was proposed. The operating principle and switch modes of the SIDO Buck LED driver were analyzed, and its state space average model and small signal model were established with the state space averaging method. Then, the circuit structure and operating principle of the I²-controlled SIDO Buck LED driver were analyzed. Based on inductive current ripple and output current ripple, the small signal expressions of duty cycle and cross regulation transfer functions were obtained. The Bode plots of the cross regulation transfer functions were employed to analyze the cross regulation compared with the output branches of the voltage-controlled SIDO Buck LED driver. The study results show that when the reference signal of LED₁ of the voltage-controlled SIDO Buck LED driver steps down from 1.6 V to 0.8 V and 2.4 V to 1.2 V respectively, the cross regulation between LED₁ and LED₂ is 0.250 A and 0.365 A, and that of the I²-controlled SIDO Buck LED driver is 0.09 A and 0.115 A. When the reference signal of LED₂ steps down from 3.2 V to 1.6 V and 2.4 V to 1.2 V respectively, the cross regulation between LED₂ and LED₁ is 0.06 A and 0.04 A, and that of I²-controlled SIDO Buck LED driver is 0.03 A and 0.015 A. It illustrates that the cross regulation between output branches of the I²-controlled SIDO Buck LED driver has been reduced compared with that of the voltage-controlled SIDO Buck LED driver.

Electric vehicle (EV) swapping stations can achieve economic benefits while also supporting the power grid by serving as energy storage stations. However, there is currently a lack of research on the capacity configuration of such EV storage and swapping integrated stations (EVSS-IS). To this end, the working mode and tariff period of EVSS-IS were firstly analyzed to build an operational model. Then, a predictive model for EV swapping demand was developed based on user travel simulations. Next, a bi-level capacity programming model of the EVSS-IS was established, which considered life cycle benefits and grid support capacity. Specifically, the outer planning aimed at the total revenue during the whole life cycle to optimize the capacity of the EVSS-IS; the inner planning aimed at supporting the power grid and optimizing the charging and discharging behaviors; the optimal charging and discharging power from the inner layer was returned to the outer layer to realize the optimal capacity programming of the EVSS-IS. Finally, the effectiveness of the planning model was verified on the IEEE33 node system, which provided theoretical support for the construction of the EVSS-IS. The results show that the return on investment of the EVSS-IS is 1.51%–2.26% higher compared with other models; the capacity optimization allocation method based on bi-level planning can support the grid voltage while ensuring the economy of the station, resulting in a 20% reduction in the daily variance of the voltage; as the number of EVs swapping batteries increases, the economics of the EVSS-IS is further improved.

In order to improve the accuracy and real-time performance of obstacle avoidance for quad-rotor helicopters, an obstacle avoidance algorithm combining the Lucas-Kanade (LK) optical flow method and maximization idea was proposed. Firstly, the video stream collected by the quad-rotor helicopter was preprocessed to obtain the image frame. Secondly, corner points whose optical flow was less than the threshold value in the image frame were eliminated by the LK optical flow method, and corner points were grouped by a clustering algorithm based on corner point distance. In addition, the outsourcing contour of each group of corner points was calculated. Then, the safe obstacle avoidance domain algorithm based on the maximization idea was used to calculate the optimal passing domain, and the deviation data were obtained according to the obstacle avoidance domain. Finally, the deviation data were input to the proportional and differential (PD) controller to obtain the control information, and the control command was sent to make the quad-rotor helicopter adjust the flight attitude in time to complete the obstacle avoidance flight. Experiments on the Tello quad-rotor helicopter in different scenes show that the proposed algorithm takes an average of 0.17 seconds to calculate the optimal safe obstacle avoidance domain for each frame of the image, which meets the real-time requirements of unmanned aerial vehicle (UAV) obstacle avoidance and solves the problem of identifying obstacle domains and calculating safe obstacle avoidance domain.

Deep learning-based intrusion detection for the train communication network requires sufficient training samples, but there are few available attack samples in the actual scenario. Generative adversarial network (GAN) thus operates to generate attack samples. Also, the sampling strategy, constraint condition and loss function of GAN are improved; and a generator based on convolutional neural network and a discriminator are designed. Then an improved GAN-based method is proposed for attack sample generation. Sample generation experiments and intrusion detection experiments are conducted to test the proposed method, indicating that it can generate effective attack samples. When applying these generated samples in the training process of the intrusion detection model, the average F₁ score increase by 4.23%, which means that the detection capability is effectively improved.

Under the condition of rainfall, the water spray splashed by the tires of vehicles during driving can easily form water mist, and the visibility in front will be significantly reduced. The subjective recognition distance of the human body will be rapidly reduced, and even the wrong judgment of driving distance will lead to traffic accidents. Therefore, it is of great significance to study the influencing factors of asphalt pavement visibility on rainy days. Based on Mie’s theory, the meteorological definition of visibility was utilized, and Monte Carlo numerical simulation was performed with MATLAB software. In addition, a visibility calculation model is put forward characterized by vehicle speed, water film thickness, and pavement design parameters and then analyzed the influencing factors of visibility. The results show that on rainy days, when the water film thickness of asphalt pavement is less than 5.873 mm, the visibility caused by water mist will decrease with the increase in vehicle speed and water film thickness; among the pavement design parameters, the length of drainage path and the depth of pavement structure are positively correlated with visibility, and there is a negative correlation between road slope and visibility. It is found that the visibility reaches the minimum when the water film thickness is 5.873 mm; an improved calculation model of asphalt pavement visibility characterized by rainfall intensity, depth of pavement structure, pavement slope, length of drainage path, and vehicle speed is proposed.

Transit travel demand has an important characteristic of being stochastic. The decision-makers with different risk attitudes (i.e., risk-neutral, risk-averse, and risk-seeking) will choose various transit service designs in response to the stochastic demand, which seems to be especially critical in the phased transit design. In order to study the impacts of stochastic travel demand on the transit service design, we firstly propose a mean-variance based decision-making approach for decision-makers with different risk attitudes. Correspondingly, the study proposes a model for phased transit corridor design, which can concurrently optimize the line length, transit station location, and headway in each phase. Then, the local decomposition method and optimization theory are adopted to find the analytical solution. Finally, the study compares the transit corridor designs with different design strategies (i.e., full-covered, once-and-done, and phased designs of the transit line) and risk decision-making attitudes. The results indicate: 1) the phased design has a lower expected system cost than the full-covered and the once-and-done designs, and a more robust scheme than the once-and-done design; and 2) risk decision- making attitudes substantially affect the parameters (i.e., the transit length, station location, and headway) of transit system under different design strategies; for example, the risk-averse decision-makers tend to seek denser station locations in the full-covered design, but relatively lower station density in the once-and-done design in phased design. The issue becomes more complex in the phased transit design. This study serves to provide a risk-based decision-making model of phased transit service under the increasing stochastic demand for the government manager and transit operators.

In order to study the thermal characteristics of the interface composed of steel and basalt fiber polymer concrete (BFPC) under oil medium conditions, the discrete principle was first used to calculate the actual contact area of the steel-BFPC interface. Since the contact surface is essentially a micro convex contact, the micro convex body is subjected to certain extrusion, forming an area with different extrusion stresses. Therefore, the accuracy of the actual contact area was further improved while considering the specific gravity of contact. Then, based on the morphology characteristics of the interface and Fourier’s law, the heat transfer mechanism of the steel-BFPC interface under oil medium conditions was analyzed. Finally, the influence of different loads (0.2, 0.4, 0.6, 0.8, and 1.0 MPa) on the thermal characteristic parameters of the interface was analyzed through theoretical calculation and experimental research. The results show that with the increase in load, the contact thermal resistance decreases, and the heat transfer coefficient and thermal conductivity coefficient increase. Under different loads, the error of contact thermal resistance between theoretical calculation and experimental calculation is 6.40%, 6.18%, 5.85%, 4.61%, and 3.73%, respectively. The error of contact thermal resistance decreases with increasing load.

The neglect of the imaginary stiffness and frequency-dependent characteristic of parameters of viscoelastic materials for the damping layer of the constrained damping structure will result in the error of the modal loss factor of the structure. The influence of the imaginary stiffness and frequency-dependent characteristic of parameters of viscoelastic materials on the modes of vibration, natural frequencies, and modal loss factors of the constrained damping plate was investigated by using the revised modal strain energy (RMSE) method and iterative algorithm. Moreover, the influence of the thickness of the damping layer and that of the constrained layer of the constrained damping plate on the modal loss factor of the structure was discussed. The results show that the natural frequency and modal loss factor calculated by the method in the paper are in good agreement with the experimentally measured values in the related literature. The modal shapes at all orders are not changed, but a reversal of the phase of several modes of vibration occurs if the frequency-dependent characteristic of parameters of viscoelastic materials is ignored. The shear modulus of the damping layer directly affects the natural frequency of the structure. If the frequency-dependent characteristic is ignored, the calculation results will be overestimated by 17.2% at the lower-order modal and underestimated by 7.6% at the higher-order modal. The maximum error of the modal loss factor is up to 56.0% at lower order modal when the frequency-dependent characteristic of the viscoelastic material is ignored. The modal loss factor of the constrained damping plate increases with the damping layer thickness and first goes up and then goes down with the constrained layer thickness.

In order to eliminate mechanical friction in the mobile laser table for micro machining, a new maglev platform jointly driven by three sets of levitated subunits was proposed in this paper. Firstly, the platform structure and working principle were introduced. The three sets of subunits had the same structure, consisting of permanent magnets and electromagnetic coils; the force of the coils applying on the permanent magnets was analyzed, and the plane range in which the maglev platform could achieve stable levitation was discussed. Secondly, the in-plane dynamics model of the maglev platform was established, and the equation of the transformation relationship between the displacement of the subunit and that of the platform was built. Subsequently, based on the decentralized control strategy, the corresponding fuzzy proportional-derivative controller of the subunit system was designed. Finally, a physical platform was built, and the static levitation experiment, step response experiment, and two-axis combined working experiment were conducted on the platform. The results show that the maglev platform can ignore the motion control in the vertical direction within the plane range of ±2 mm, and it has a root mean squared error in the x direction of only 2.95 μm and a maximum tracking error of 11 μm during static levitation. Meanwhile, the maglev platform has a motion displacement of 4 mm and two-axis combined working ability.

A density-reducing Monte Carlo method was proposed to address the problems of inaccurate precision and waste of encrypted point cloud in the Monte Carlo method and the improved Monte Carlo method for solving robot arm workspace. Firstly, based on the characteristic of uneven distribution of random points in the Monte Carlo method, the initial workspace of the robot arm was uniformly densified to make the inner and boundary regions of the space clear. Then, only the boundary region was encrypted by adopting the extended joint angle and the cyclic encryption of random points, so as to reduce the density of the random point cloud in the workspace. Meanwhile, the influence of initial point cloud quantity, axial segmentation voxel quantity, precision threshold, extended joint angle, and cycle number on the precision of the workspace was studied. Finally, the effectiveness of the density-reducing Monte Carlo method was verified by simulation analysis. The results show that compared with the Monte Carlo method, the total number of random point clouds of the density-reducing Monte Carlo method decreases by 93.89% when the average error rate of the workspace is 0.022 42%. In addition, compared with the improved Monte Carlo method, the density-reducing Monte Carlo method reduces the average error rate of the workspace by 0.138 53% and 0.113 29% when the number of cycles is 2 and 4, and the total number of random point clouds decreases by 44.83% and 64.52%.

In order to study the rolling fatigue damage (RCF) of heavy-haul locomotive wheels, the three-dimensional heavy-haul locomotive–track coupled dynamics model was established, and the dynamic interaction behavior of locomotive wheel–rail system under the condition of wheel polygonal wear and different rail surface frictions was studied. On this basis, a wheel tread RCF prediction model based on the dynamic responses of the wheel–rail system was established, and the effect of wheel polygonal wear on the wheel surface wear was studied under the changing wheel–rail friction conditions with the braking effort. The results suggest that the wheel polygonal wear not only intensifies wheel–rail dynamic interaction but also increases wheel–rail interface wear and damage. The wheel polygonal wear can aggravate the wheel tread RCF under the dry contact condition. The fluctuation range of the damage index of the locomotive with one and four wheelsets increases by 19.59% and 39.43% compared with that of a normal wheel. Under the low-adhesion contact condition, the wheel polygonal wear can aggravate the wheel wear, and the fluctuation range of wheel–rail creep force increases 5.85 times. The fluctuation range of the wear number of the locomotive with one and four wheelsets improves 6.44 times and 6.22 times, respectively.

In order to make the effect of tamping operation meet the expected goals, it is necessary to strictly control the unfavorable factors affecting the quality of the operation. Firstly, by taking the tamping operation data of ballasted track as the research object, the key factors affecting the operation quality were analyzed firstly, and the basic principles of the traditional methods to correct the lifting scheme were discussed. Secondly, by incorporating the multi-factor constraints into the target line construction process and correcting the lifting value according to the historical operation law, a comprehensive correction method of the lifting scheme for improving the adjustment effect of track height was constructed. Finally, by taking the ballasted track tamping operation of a high-speed railway as the engineering background, the implementation effect of the comprehensive correction method was verified. The results show that the application of targeted control measures in the process of lifting scheme formulation can improve the ability of the tamping operation to adjust the track irregularity. The coefficient of determination between the measured value and the target value of the alignment after tamping is as high as 0.92, and the mean square error between the planned lifting value and the actual lifting value is only 1.8 mm. The mid-chord value of 60 m is reduced to 4.0 mm, and the track quality index is reduced to 0.28 mm.

Wheel out-of-roundness (OOR), which is commonly observed on the wheels of Chinese high-speed trains, has a significant influence on the vehicle ride comfort and operation safety. From 2011 to 2020, 30500 wheels of nine types of high-speed trains were selected for tests and the wheel OOR was measured. The tested high-speed trains operated on 12 high-speed railway lines with different operating speeds, including operating speeds of 200, 250, 300, and 350 km/h. The characteristics of the wheel OOR were analyzed to determine the development rules for wheel polygonal wear of high-speed EMUs in China. The key factors that affect the wheel polygon wear were analyzed, including the wheelbase, track structure, and abrasive block. The test results show that the dominant harmonic orders of the wheel polygonal wear range from 10^th to 30^th order. The corresponding wavelengths of the 10^th–30^th-order polygonization are 90–288 mm, with a wheel polygonal wear of 100‒178 mm being the most severe. The analysis of the key factors that affect the wheel polygonal wear shows that the wheelbase, fastening stiffness, and ambient temperature are closely related to the formation of wheel polygonal wear. By improving the matching relationship between the abrasive block and the wheel tread, the transverse and circumferential wear is minimized and the roughness level of the high-order polygonal wear is reduced by 60% at most.

With the continuous breakthrough and development of intelligent connected vehicle technologies, highly automated self-driving cars have gradually matured and entered public life. Different from manual driving cars, self-driving cars integrate the functions of environmental perception, independent decision-making, as well as control and execution. As a result, it can complete the self-driving for typical or all roadway conditions. The improvement and adjustment in roadway facilities will help to speed up the arrival of the self-driving era. Therefore, it is necessary to clarify the demand and impact of self-driving cars on the design of roadway facilities. Firstly, how the roadway facilities adapt to the driving behavior of self-driving cars was analyzed from five aspects such as horizontal and vertical alignment, cross-section design, traffic signs and markings, parking facilities, and digital roadway facilities. Secondly, the status and development trends of smart roadside facilities and self-driving exclusive lanes were summed up. Then, the research methods of roadway facilities for self-driving cars in China and abroad were summarized, including virtual simulation tests and field driving tests, and the experimental roadways constructed for field driving tests around the world were reviewed. Finally, the focus of and the limitations of existing research were summarized, and the challenges and future development trends of this research field were prospected. The planning and design of existing roadway facilities do not foresee the arrival of self-driving cars; before the widespread popularization of self-driving, manual driving and self-driving cars will coexist for a long time. Therefore, roadway facilities should be designed according to the development stage and future trends of self-driving. This work provides a theoretical basis for roadway facility design adapted to self-driving cars.

Ruts can be one of the key reasons for early damage of asphalt pavement. Due to the channelized traffic characteristics of aircraft taxiing, the evenness and comfort of airport pavement are notably affected by rut damage. In this paper, a simulation analysis model of aircraft landing gears-foundation-asphalt pavement system is established. An equivalent cyclical loading process is proposed according to the loading characteristic of landing gears. The feasibility and reliability of the simulation model are verified by the rut test result of full-scale asphalt pavement conducted by National Airport Pavement Test Facility (NAPTF). Factors such as the loading interval and environment temperature are then analyzed. The results show that due to lateral shift effect of landing gear load, the total width of the ruts reaches 3 times the width of the landing gears, and the rut section curve has many turning points, which is obviously different from those of the previous single concave surface. The cyclical loading interval has a remarkable influence on rut development. The rebound deformation of the asphalt surface course becomes stable after a loading interval of 150 s, which can meet the requirement of analysis efficiency. Since the first 10% number of cyclical loading contributes more than 40.4% of overall rut deformation, an exponential rut deformation prediction formula is derived based on initial ruts. The goodness of fit result during the whole cyclical loading process is over 96.4%, and the efficiency of rut analysis is dramatically increased.

In order to explore the long-term monitoring method of bi-block ballastless track sleeper pressure, this paper took the CRTSⅠ bi-block sleeper as the research object and studied the linear relationship between the internal strain values and the sleeper pressure by using the embedded fiber Bragg grating sensor. Firstly, the fiber reinforced polymer-optical fiber (FRP-OF) strain sensor was embedded in the sleeper at the manufacturing stage. Secondly, the sleeper was calibrated under static load by the reaction rack and jack, and the linear relationship between the surface loading force and the internal strain of the sleeper was analyzed. Finally, the finite element simulation was used for verification and correction. The results show that the load applied on the sleeper surface has a good linear relationship with the measured value of the FRP-OF strain sensor inside the sleeper. The slope of this linearity is determined as the calibration coefficient, with a range of about 4.90–5.28 kN/με. The error rate between simulation data and measured data is within 5%. The internal strains of the sleeper are compared under two different boundary conditions: reaction frame constraint and track slab constraint, and the equation for calculating sleeper pressure is corrected. As a result, a calculation method of sleeper pressure based on the internal strain of a bi-block sleeper is presented, and the sleeper pressure measured on a high-speed railway operating line is about 30–42 kN. This method provides an important basis for studying the wheel/rail force transfer, improving strength calculation theory and method of ballastless track structures, and monitoring the condition of wheels of high-speed railways.

In order to study the deterioration law of the red-bed soil-rock mixture (RB-SRM) under wetting-drying cycles, the RB-SRM in Sichuan Basin was considered as the research object. The disintegration characteristics of red-bed soft rock blocks with different particle sizes were discussed through static disintegration tests. The original gradation scale of two groups of red-bed soil-rock mixed subgrade fillers was studied. The effects of wetting-drying cycle times on the cohesion, internal friction angle, dilation rate, and shear modulus of RB-SRM were studied by the laminated shear test. The results show that the red-bed soft rock block disintegrates significantly in water, and the disintegration process can be divided into the severe stage, transitional stage, and stable stage. The content of the disintegrated rock block in the severe stage is reduced by nearly 70%; for rock block with a larger particle size, it is more affected by the structural plane, and the disintegration is more significant. With the increase in the number of wetting-drying cycles, the shear strength is significantly reduced in the severe stage, while that in the transitional stage is basically unchanged and slightly recovered in the stable stage. After the disintegration of the rock block, the interlocking is significantly reduced; the apparent adhesion is sharply reduced, and the electrostatic attraction and the curing cementation slightly increase the cohesion. The friction and the redirection arrangement among the disintegrated RB-SRM slightly improve the internal friction angle. The maximum particle size and content of rock blocks are significantly reduced so that the RB-SRM is denser, and the dilation rate is significantly reduced under normal stress. Meanwhile, the skeleton-dense structure is transformed into a suspension-dense structure, and the shear modulus is significantly reduced. The degradation of cohesion and dilation rate under wetting-drying cycles is more obvious. The deterioration of the internal friction angle is mostly affected by the particle size of the blocks, and that of the shear modulus is least affected. Before embankment filling, it is suggested to disintegrate the RB-SRM twice to reduce the adverse effect of rainfall-evaporation cycles.

In order to explore the shrinkage and deformation laws of early-age concrete under large dry-cold temperature differences and reduce the risk of cracking, three curing methods were used for early-age curing of concrete. The compressive strength, splitting tensile strength, free shrinkage rate, and maximum restraint stress were used as the characterization methods. Basic mechanical performance test, free shrinkage test, and restraint shrinkage test were designed. The comprehensive multi-index grey correlation method was adopted to analyze the anti-cracking performance of concrete under different curing methods. In addition, a nano-coating thermal insulation performance test was designed to explore its thermal insulation performance on concrete. The test results show that the use of nano-coating reduces the average temperature difference inside the cylindrical concrete specimen by 2.95 ℃ in the circulating temperature of ‒20.0–15.0 ℃; compared with those under standard curing, the compressive and splitting tensile strengths of concrete under the three curing methods are significantly reduced, and the large dry-cold temperature difference is not conducive to the strength development of concrete. The free shrinkage rate changes significantly with temperature. Specifically, as the temperature decreases, the free shrinkage rate increases, and as the temperature rises, the free shrinkage rate decreases. In addition, extreme values appear at ‒20.0 ℃ and 15.0 ℃; the maximum restraint stress is affected by the curing method. Under natural curing, the maximum restraint stress develops the fastest, with the largest final value, followed by that under film curing. Under coating curing, the maximum restraint stress develops the slowest, with the smallest final value. The gray correlation degree under coating curing is as high as 0.9149, which is significantly higher than that under natural curing and film curing, showing excellent anti-cracking performance.

The soil-arching effect, in essence, is a stress transfer phenomenon triggered by the loosening of the internal structure of the soil. The loosening process is accompanied by the formation and expansion of slip surfaces. At present, research on the geometric contour of slip surfaces, loosening-affected areas, and influence of the dynamic evolution of loosening zones on the loosening earth pressure remains sparse. Therefore, Trapdoor tests were conducted to investigate the contour of slip surfaces and their evolution in sand under the soil-arching effect. In this way, differences in the characterization of the geometric contour of slip surfaces and their evolution modes under different filling heights, downward movements and widths of trapdoors, and sand densities were obtained. By defining a core loosening zone in the area affected by slip surfaces, a calculation method for the loosening stress based on the geometric contour of the core loosening zone was proposed. In addition, the curve characteristics of the loosening stress and downward movement of the trapdoor were analyzed to reveal the changes in curve characteristics with the filling height, downward movement and width of the trapdoor, and sand density under maximum and minimum arch states. The research results show that: 1) the contour of slip surfaces evolves from a triangle, to a bullet shape, and finally to an ellipse with the downward movement of the trapdoor. As the filling height gets greater, and the trapdoor becomes narrower, the contour of primary and secondary slip surfaces is sharper. 2) with the downward movement of the trapdoor, the height of the primary and secondary slip surfaces increases, while that of inflection points of the level-Ⅲ slip surface decreases. In addition, as the trapdoor moves downward, the angles of the primary and secondary slip surfaces both increase first and then decrease, while the upper and lower half-angles of the level-Ⅲ slip surface both increase. 3) the contour of the core loosening zone changes from a triangle, to a trapezoid, and finally to a rectangle with increasing filling height. The height of the core loosening zone is 0.5–0.8 times the filling height, and the angle and area of the zone both decrease in a quasi-linear manner with increasing internal friction angle. 4) the calculation method for the loosening stress based on the area of the core zone is more applicable than Terzaghi’s method, and it is suggested that it be used to calculate the critical stress of test groups with a low and a high filling height respectively. The research results provide more accurate descriptions and judgment criteria for the displacement and failure modes of the loosening zone in sand. They also provide a reference for evaluating the stability of the loosening zone.

The continuous beam bridge is often damaged or even collapses due to the earthquake and thus loses its traffic function. Therefore, it is important to study the damage mechanism of large-span continuous beam bridges under strong earthquakes to improve the bridge collapse resistance. Based on the finite element software ANSYS/LS-DYNA, a three-dimensional numerical model of the damage of a large-span continuous beam bridge under strong earthquakes was established, which considered the material nonlinearity of the bridge pier, the large deformation nonlinearity of the damage process, and the nonlinear collision of the beam end. In addition, nonlinear analysis was performed to visually simulate the damage process of the large-span continuous beam bridge under strong earthquakes. The seismic damage of the large-span continuous beam bridge was analyzed in terms of strain and displacement response, pier damage, and girder-platform collision. The study results show that the damage modes of the one-way ground motion input and two-way ground motion input are basically the same, and the damage mode is determined by the bridge structure, and the ground motion input mode has less influence; the seismic damage of the large-span continuous beam bridge involves a gradual development process; the concrete damage factor of the bridge pier accumulates to 0.99; the bending plastic damage occurs at the bottom of the fixed pier, and the bridge is damaged.

To study the effect of longitudinal reinforcement ratio on the flexural capacity of a one-way slab of an ultra-high performance concrete (UHPC) wafer bridge deck, six full-scale T-beam models with varying longitudinal reinforcement ratios were produced by using the principle of equivalent width to simplify the analysis. Firstly, the basic mechanical properties of UHPC were studied, followed by the flexural behavior and failure mode of T-shaped UHPC beams through loading experiments. Secondly, a constitutive model for the tensile and compressive strength of UHPC was proposed based on the results of material performance tests. Through section analysis, a formula for calculating the ultimate flexural capacity of T-shaped UHPC beams was derived. Finally, the applicability of the proposed formula was validated based on previous research results. The research findings indicate that although reducing the longitudinal reinforcement ratio will weaken the ultimate flexural capacity and ductility of T-shaped UHPC beams, the failure mode of the components will not change, and T-shaped UHPC beams will still exhibit ductile failure characteristics, even with low or no reinforcement, due to the excellent tensile strength and toughness of UHPC. Moreover, the results of section analysis derivation indicate that the coefficient of variation of the ultimate tensile strength of UHPC under tension is proportional to the longitudinal reinforcement ratio. Therefore, increasing the longitudinal reinforcement ratio can significantly enhance the tensile strength of UHPC. The proposed formula was found to be applicable.

In order to find a more suitable joint form for the concrete-filled steel tubular (CFST) lattice wind power tower, static tests of models for two flanged spherical branch joints and two flanged bolted spherical joints were carried out, and the finite element analysis was performed. By taking the height and thickness of the table as the changing parameters, the failure modes of the two kinds of joints, the equivalent stress distribution of the flange, and the axial force-deformation curve of the web rod were compared. The research results show that the failure modes of flanged spherical branch joints are shear failure of high-strength bolts, and those of flanged bolted spherical joints are table weld tear failure and buckling-tear failure. Compared with that of the flanged spherical branch joint, the equivalent stress distribution of the flange and the table of the flanged bolted spherical joint is uniform, and the material utilization rate is higher; the absolute values of the maximum stress are increased by 19% and 52%, respectively, and the bearing capacity is strong. The plastic stage of the axial force-deformation curve of the web rod is long, and the ductility is excellent. The change in the height or thickness of the table is more sensitive to the ultimate bearing capacity of the joint, and a higher ultimate bearing capacity is observed. The flanged bolted spherical joint can be promoted and widely applied.