To find out the shear bearing capacity and its calculation method of ultra-high performance concrete (UHPC) keyed joints, a full-scale model test of five UHPC keyed joints and a UHPC flat joint were carried out with the joint type and lateral compressive stress as parameters. The failure mode and the variation of shear bearing capacity of the specimens with UHPC joint were studied. Then, based on the shear-compression strength criterion of concrete, the octahedral stress formula was used to derive the formula for calculating the shear bearing capacity of UHPC keyed joints, which was then validated by the test results. Finally, the experimental data of 62 UHPC keyed joints were collected and used to verify the accuracy of the developed formula. The results show that the UHPC keyed joint is damaged by vertical major cracks developed at the root of the keys and has obvious brittle characteristics. The ultimate load of the specimen with an epoxied joint is greater than that with a dry joint by 21.3% under the same lateral compressive stress. When the lateral compressive stress increases from 3 MPa to 12 MPa, the ultimate load of the specimen with an epoxied joint increases by 26.9%. The developed formula can accurately predict the shear bearing capacity of UHPC keyed joints with low dispersion and conservative results in general. The average absolute errors of the specimen with five keyed joints are 11%, and those of 62 existing specimens are 21%.

The rockfall events on transport lines in mountainous areas occur frequently and are sudden and random. Probability-based reliability design of protective structures is a necessary and effective means to reduce the hazard risk. However, the method of determining the design value of rockfall size, as a basic parameter of the design, is still unclear, making the reliability design fail to be carried out effectively. The prediction method of rockfall size and the return period was introduced based on the Poisson-generalized Pareto distribution (GPD) composite model. According to the rockfall record data of the Bai−Upper section of Baoji−Chengdu Railway, the GPD threshold was selected, and the impact of the missing maximum and minimum rockfall sizes (vmax and vmin) in the record on the threshold selection and prediction results was analyzed. Corresponding to the exceedance probability of the standard value of earthquake action, a method of determining the design value of rockfall size was proposed, which was based on the three-level protection standard featuring “the structure doesn’t break under small rockfalls, can be repaired under medium rockfalls, and doesn’t collapse under large rockfalls”. The results show that the missing maximum rockfall size in the record has a small impact on the threshold selection but a large impact on the prediction results of the rockfall size. The prediction value of rockfall size corresponding to the return period increases exponentially with the set maximum rockfall size, while the recorded minimum rockfall size has less impact on both the threshold selection and the prediction results. By taking the record data of the Bai−Upper section of Baoji−Chengdu Railway as an example, according to the selected reasonable threshold, different maximum rockfall size values are set. By using the method presented in this paper, the interval range of rockfall size in return periods of 50, 100, 1 000, and 10 000 years on the Bai−Upper section of Baoji−Chengdu Railway is predicted, and the standard value (design value) of rockfall size corresponding to the three-level protection standard in design reference periods of 50 and 100 years is calculated, which can provide a reference for similar engineering designs.

To address the issue of settlement and cracking of adjacent roads during the excavation of urban foundation pits, the research object was extended from a one-dimensional structure to a two-dimensional structure based on the Winkler theory. Firstly, a calculation model for the settlement field caused by foundation pit excavation was established, and the control equation for road flexural deformation was derived. Secondly, a two-stage analysis method was adopted by considering factors of foundation pit excavation depth, aspect ratio, support stiffness, and thickness of soft soil layer above the pit bottom, so as to provide a correction formula for settlement field caused by foundation pit excavation and a method for predicting maximum surface settlement. Thirdly, the settlement field was substituted into the control equation for road flexural deformation, and a fourth-order nonlinear partial differential equation was solved by using the finite difference method. Finally, the above road calculation and analysis model under the condition of foundation pit excavation was verified by an engineering example. By comparing the field monitoring data with the theoretical solution and numerical simulation, it was found that the errors in road settlement were 15% and 8.3%, respectively, both of which are within acceptable limits, thereby confirming the reliability of the road calculation and analysis model proposed in this study under the condition of foundation pit excavation.

Hazard susceptibility assessment is generally a probabilistic modeling based on the spatial distribution characteristics of hazards, but the hazards have spatial heterogeneity. In order to solve the spatial heterogeneity of hazards, the collapses and landslides along the Wenchuan−Lixian section in the Wenchuan−Maerkang Expressway were studied. By using the K-means algorithm, the hazard-threaten objects (people and property) and risk degree (damaged house area and damaged road length) in the study area were spatially clustered, and different clustering attributes were assigned to the study area. Then, nine factors including slope angle, elevation, slope aspect, curvature, surface cutting degree, river curvature coefficient, distance from the tectonic zone, bank slope structure, and formation lithology were selected in terms of hydrology, geology, and geomorphic conditions. The samples were divided into 70% training data and 30% test data. The performance of the K-RF model and the traditional random forest (RF) model in susceptibility assessment was compared to provide theoretical support for operation safety and hazard prevention of expressways. The results show that the K-RF model contains a total of 82.95% of the hazard points in the areas with extremely high susceptibility, which has better assessment results than the single RF model (with AUC value increased by 5.4%). Therefore, it is feasible to use clustering to solve the spatial heterogeneity of hazards. However, the research limitation is that it fails to reflect the spatial heterogeneity of hazards from the hazard itself. The coupled model is a comprehensive reflection of susceptibility and vulnerability in essence.

In order to further study the influence of site effects from engineering ground motion, a comparative analysis of site effects from ground motion in the Sichuan strong earthquake area was carried out based on two empirical methods, namely, horizontal-to-vertical spectral ratio (HVSR) and linear inversion. Firstly, 233 sets of strong motion waveforms captured by 17 strong motion stations during the aftershocks of the Wenchuan Earthquake were selected based on the magnitude, station, distance from the epicenter, and other factors. Second, the linear inversion method was used to estimate the quality factor Q_s of the S-wave based on the hinged three-stage attenuation model in the Longmenshan area. Meanwhile, two methods, rotational HVSR and multidirectional HVSR, were applied to explain the mechanism of the site effect of azimuthal angle on HVSR in seismic wave propagation. Finally, the possible reasons for the variability of the site effects calculated by the linear inversion and HVSR methods were analyzed, based on which an improved HVSR method was proposed to improve the accuracy of the site effect assessment. The results show that the quality factor of the S-wave in the area is frequency-dependent and approximately equals to 199.2f ^0.8 in the range of 0.4–20.0 Hz. The results of HVSR may have a certain dominant direction, and the site effect may increase suddenly at a certain angle with the change of the azimuthal angle, which may be related to the anisotropy of the soil layer at the site. The amplification of vertical ground motion, i.e., the vertical site effect formed by the coupling of soil layer at the site, engineered bedrock, or middle and deep hard rock layers, is the main reason for the difference between HVSR and linear inversion methods.

In the electric truck route planning problem with time windows, electric trucks may need to queue up when they go to charging stations for charging. To study the impact of different charging station configuration schemes on vehicle route planning and system performance, the queuing model was first built to describe the queuing phenomenon at charging stations. Then, a route optimization model was established by considering the power and flow constraints based on the electric truck route planning problem with time windows, with the queuing model of charging stations embedded into the optimization model. The optimization goals included minimizing vehicle power consumption costs, driver’s wages, penalty costs of time windows, and total costs of all charging piles. To solve the model, a hybrid heuristic algorithm combining mileage saving (C-W) and improved large neighborhood search (LNS) was designed, and the system performance metrics of charging stations were obtained by a recursive algorithm. 18 sets of experimental results show that increasing the number of charging piles simultaneously can control the average queuing time of a vehicle for charging within 1–5 minutes and effectively reduce the total cost by 2.6%–21.0%; increasing the number of charging stations can reduce the queuing time but increase the total cost of the entire route; when the customer time window is short, or the service time is long, the change in the number of charging piles has a more significant impact on the satisfaction of the time window.

In view of non-uniform operation rules of ship locks and non-synchronous ship scheduling in the joint navigation scheduling of cascade hubs, a multi-dimensional nonlinear programming (MDNP) model considering ship priority was constructed with the comprehensive navigation efficiency of ships, the cost of waiting for lock opening, and the carbon emission as the decision-making objectives. Then, the improved backtracking multi-objective simulated annealing algorithm (IBMOSA) was used to solve the MDNP, and the optimization scheme for joint scheduling of cascade hubs was proposed. Finally, the effectiveness and reliability of the MDNP model and IBMOSA were verified by taking the “Three Gorges-Gezhouba” Cascade Hub as an example. The results show that the MDNP model can effectively take into account the navigation efficiency of ships and fairness, and IBMOSA has good convergence and global property. At the same time, through the coordinated drainage sluice plan formulation, the opening of each lock is reasonably arranged, which avoids the phenomenon of switching operation of cascade locks and reduces the overall dam crossing time of ships. Compared with that of the original scheduling scheme, the optimization efficiency of the three decision-making objectives of the joint scheduling scheme is nearly 40%, and the traffic congestion relief rate of cascade hubs is about 16%, which effectively solves the navigation contradiction among cascade hubs and improves the overall navigation efficiency of the Three Gorges water area.

In order to explore the variation of the vulnerability of the en-route network caused by cascading failure, the vulnerability of the en-route network was analyzed based on the cascading failure process of different attack methods. By combining with the actual overcapacity operation of the en-route network, the overload operation of the nodes in the non-failure state, the probability of node failure, and the divertability of the load passed by the nodes were extracted. The cascading failure model of the en-route network and the cascading failure process based on different attack methods were constructed, and the en-route network-level vulnerability index was proposed from the perspective of the loss of waypoint operation capacity, as well as the vulnerability analysis method combined with the cascading failure model. The correlation between the vulnerability of the en-route network and the proposed model parameters was analyzed by studying the operation data in Eastern China, and the change rule of the vulnerability index of the en-route network under different parameters was explored. Three kinds of attack experiments were designed, and the results show that the operation capacity of each waypoint increases with the overcapacity range of the load flow, and the vulnerability of the en-route network decreases; the en-route network is more sensitive to selective attack methods, especially those based on the betweenness.

Land use type in China is complex, and it is difficult to accurately identify urban land use type by relying on a single remote sensing image or point of interest (POI) data. To address this issue, a fine identification method combining remote sensing images and POI data was proposed. Firstly, to finely identify urban land parcel functions, a 500-meter grid was selected as the research unit; secondly, POI data were extracted, and kernel density distribution maps of various land uses were generated. Data preprocessing, data segmentation, and data enhancement were performed on remote sensing and POI image data to extract effective information. Finally, the POI kernel density distribution map and high-resolution remote sensing image data were fused together, and the current land use data was used as the label to construct the UNet++ network to classify urban land parcels. The model parameters were optimized using the cosine annealing (CA) algorithm, and the proposed method was tested in Shenzhen City. Migration verification was carried out in Luohu District and Nanshan District. The results show that the average accuracy of the urban land use identification model fused with POI data is 70.6%, which is 6.7% higher than that of the identification model using only remote sensing data; after using the CA algorithm, the model accuracy is increased by 1.5%. The migration verification of the model is carried out, and the average accuracy of the model is 72.6%. This shows that the model is robust. In addition, POI data makes up for the shortcomings of remote sensing images that only involve spectrum, texture, and physical attributes of ground structures, and it can better identify commercial land and public management and service land. The accuracy is 7.5% and 6.0% higher than that of a single data identification model.

The service environment of alpine electric multiple units (EMUs) is affected by temperature for a long time, and the vehicle suspension element parameters and under-rail parameters have strong seasonal variation characteristics. To investigate the influence of temperature-varying characteristics of rubber elements on the operating performance of alpine EMUs, a multi-body dynamics model of alpine EMUs was established to analyze the vehicle dynamics characteristics under different temperatures. Then, the wheel wear characteristics at different temperatures were analyzed by the Jendel wear model. Finally, the wheel surface fatigue index was proposed based on the fatigue prediction model. The results show that the temperature variation will change the stiffness and damping value of suspension parameters, and the stiffness of suspension parameters increases as the temperature decreases. The dynamic performance of the EMUs decreases at low temperatures. The wear of the vehicle increases as the temperature decreases. After 200 000 miles of operation, the largest depth of wheel wear is found at a temperature of −40 ℃, which is 6.2% greater than the depth of wheel wear at a temperature of 20 ℃. The surface contact fatigue index gradually increases as the temperature decreases, with wheel surface fatigue indexes being 6.4648×10⁻⁴, 6.6150×10⁻⁴, and 6.7885×10⁻⁴ at temperatures of 20 ℃, −20 ℃, and −40 ℃, respectively. Temperature-varying characteristics have a large effect on the suspension parameters of alpine EMUs, with dynamic performance deteriorating at low temperatures, wear intensifying, and wheel surface fatigue increasing.

Wheel-rail profile compatibility has an important influence on the dynamic performance of rail vehicles. The present standard JM₃ wheel profile has a large difference in equivalent conicity when it is matched with different types of rail profiles in China. It has the problem of locomotive swaying caused by too low equivalent conicity when the profile is matched with the grinding rail with large rail cant. To address these issues, the optimization objective of reducing the equivalent conicity dispersion of the wheel profile matched with CN60 and CN60N rail profiles under different rail cants was set. The wheel profile was described by a method combining arcs and straight lines. The JM₃ wheel profile was optimized by utilizing NSGA-II genetic algorithm to improve the lateral position parameters of the two arc centers near the rolling circle. The wheel-rail contact characteristics and the locomotive dynamic simulation of the wheel profile before and after optimization were compared. The results show that when the optimized wheel profile is matched with the rails above, the nominal equivalent conicities at the 3 mm transverse displacement of the wheelset are all about 0.1, which reduces the equivalent conicity dispersion of the original JM₃ wheel profile and improves the adaptability of the wheel profile to different rail profiles and line conditions. At the same time, the locomotive hunting stability, lateral stability, curving performance, and wear performance index of the optimized profile are all improved compared with the original wheel profile. In addition, the phenomenon of low-frequency swaying of locomotives on specific lines is eliminated.

To reduce insufficient displacement in the contact area between the movable point frog’s point rail and wing rail, minimize transition force at the transition points of point rail, and improve the frog’s longitudinal smoothness, an optimization method for the design parameters and key components of movable point frogs was proposed. The minimum flangeway width of the No.18 movable point frog was selected as the optimization target. Based on the existing structural parameters and finite element method, a model for point rail transition calculation was established, and the method of successive approximation was used to optimize the design method of the transition displacement curve of the point rail. Under the different frog form and position tolerances for both straight/diverging lines, an optimized design was proposed with a second traction point stroke of 50.7 mm, along with the structural design scheme for key components of the frog in the straight-through state. The results show that the maximum deviation between calculated and designed point rail transition displacements is 6.64 mm, occurring at the elastic bending center. The computed minimum flangeway width (90.7 mm) closely matches the measured average value (90.9 mm), ensuring safe vehicle passage. Additionally, the second traction point stroke is reduced by 8.3 mm compared to existing frog designs, lowering the required transition force at the second traction point.

Rail grinding occurs when the rail grinder is in traveling status, which is affected by the dynamic performance of the vehicle. Rail grinding is generally set as constant power grinding, involving a wheel-track contact relationship, wheel-track grinding relationship, hydraulic system, and control system. It is a mechanical-electric-hydraulic coupling process. The whole model of rail grinding based on mechanical-electric-hydraulic coupling was formed by considering the mechanical-electric-hydraulic coupling of the rail grinding process on the basis of vehicle-track coupling dynamics. This model included a vehicle-track coupling dynamics submodel, wheel-track contact submodel, grinding submodel, and hydraulic system submodel. This rail grinding model was validated by comparing it with experimental data. The results show that in vehicle-track dynamics model verification, the maximum deviation of derailment coefficient is 11.11%, and the maximum deviation of wheel unloading rate is 7.69%. The maximum deviation of the lateral force of the wheel is 11.68%. In hydraulic and control model verification, under 0.7 Hz and 1.7 Hz rail corrugation, the deviation range of pressure in the rodless cavity are between (−2.96%–2.92%) and (−0.32%–1.38%), and the deviation range of flow in the rodless cavity are between (−24.11%–0) and (−48.72%–0). In grinding model verification, the trend is generally consistent, with a deviation of 0.036 mm at the point of maximum deviation. The above deviations are all within the acceptable range, proving that this model can be applied to practical rail grinding study.

The hydro-pneumatic suspension has the functions of cushioning and damping, body attitude adjustment, etc., but its structure is complex, with large pressure impact and high wear resistance and sealing. The excellent suspension cylinder structure, hydro-pneumatic suspension system, and control method are the important conditions to determine the driving performance of the vehicle. The type of hydro-pneumatic suspension was analyzed, and the classification and principle of hydro-pneumatic suspension were summarized from the aspects of suspension structure, working characteristics, and control mode. From the perspective of suspension controllability, the hydro-pneumatic suspension technology was discussed in terms of structural design and optimization of hydro-pneumatic suspension, mathematical modelling, and control algorithm and strategy. By analyzing the characteristics and shortcomings of existing structures, it is concluded that passive suspension is simple in structure and mature in technology, but it lacks adaptability. The semi-active suspension has low energy consumption, low cost, fast response, and high reliability, but its adaptability is limited. Active suspension has excellent performance, but it has high energy consumption, high cost, and complex system structure and control strategy. The development status and research direction of the three types of suspension were summarized and prospected, so as to provide a reference for the further research and development of vehicle hydro-pneumatic suspension design and control methods.

Mining dump trucks are mainly used for small-scale mine transportation, often run on poor roads or with serious overloading and other conditions. Hydro-pneumatic suspension is widely used in large construction vehicles due to its nonlinear characteristics of stiffness and damping, which can better adapt to external load excitation changes. For the XDR80t mining dump truck produced by XCMG, the acceleration data of the tire center of mass and body were collected, and a method based on frequency domain integral was proposed to obtain the relative displacement data of the piston rod. AMESim simulation platform was used to establish a mechanical and hydraulic co-simulation model, and the variation trend of body vibration characteristics under different structural parameters of suspension was investigated. The results show that the damping hole diameter has a more obvious influence on the vibration state of the body. When the damping hole diameter is changed from 8 mm to 14 mm, the peak value of acceleration is reduced by about 49.27%, and the root mean square (RMS) value is reduced by about 49.42%. However, the pitch angle shows an increasing trend. With the increase in cylinder/rod diameter from 180/150 mm to 200/170 mm, the peak value of acceleration and RMS value decrease by 16.84% and 18.62%. When the pre-charge pressure is increased from 1.5 MPa to 2.25 MPa, the peak value of acceleration and RMS value decrease by 27.67% and 27.49%, and the pitch angle declines.

The wheel-rail interaction force is the key index to evaluate the operation quality of rail vehicles. An identification method based on the square root cubature Kalman filter (SRCKF) algorithm was proposed for online monitoring of the wheel-rail vertical force of rail vehicles. By taking the vehicle-track vertical coupled dynamics model considering the nonlinearity of suspension elements as an example, a nonlinear process function of wheel-rail vertical forces and state variables of vehicle components was established. The vertical accelerations of the vehicle body, frame, and wheelset were adopted as observations, and the SRCKF algorithm was employed for the recursive estimation of wheel-rail vertical forces. Furthermore, a vehicle dynamics model and its corresponding wheel-rail vertical force estimation model of 17 degrees of freedom were established to identify the vehicle’s left and right wheel-rail vertical forces under actual irregularity excitation. Simulation results indicate that the proposed method can precisely identify wheel-rail vertical forces of vehicles excited by the random irregularity, rail corrugation irregularity, and rail weld irregularity, with the identified value of wheel-rail vertical forces is in good agreement with the simulation value in both time domain and frequency domain. The correlation coefficients are 0.988, 0.999, and 0.969, respectively. When the proposed method is used to identify the vehicle’s wheel-rail vertical force, the lowest correlation coefficients of the left and right wheel-rail vertical forces are 0.747 and 0.720, respectively, and the correlation coefficient of the sum of the left and right wheel-rail vertical forces is 0.999.

Cr alloy seal ring and YG-6 cemented carbide seal ring were used to pair with impregnated graphite seal ring in a petrochemical pump at 300–400 ℃, respectively. It was found that the Cr alloy seal ring maintained good sealing performance for a long-term service, while gas leakage occurred to the cemented carbide seal ring after a short time of service. To explore the reasons for the difference in service performance of two kinds of alloy seal rings, the surface morphologies, chemical compositions, and mechanical properties of the failed seal rings were characterized, and their failure mechanisms were analyzed. The results show that the Cr alloy seal ring is made from martensitic Cr-containing steel without surface strengthening treatment, and the surface hardness and elastic modulus are (629.8±14.2) HV30 and (244.7±17.4) GPa, respectively. On its contact area with impregnated graphite, an annular wear scar characterized by a slight ploughing effect is observed, and the surface roughness of the wear significantly decreases. The surface hardness and elastic modulus of the cemented carbide seal ring are (1475.3±60.1) HV30 and (815.3±57.2) GPa, respectively. There exists high residual stress and material embrittlement induced by oxidative corrosion in the seal ring surface. No obvious wear occurs on the contact area with impregnated graphite, but blocky defects caused by oxidation cracking appear. Due to low stiffness and high surface roughness, the Cr alloy seal ring suffers from abrasive wear on its surface with impregnated graphite, but the wear surface has grinding and polishing behaviors, maintaining its good sealing performance when paired with impregnated graphite. For the YG-6 cemented carbide seal ring, defects by cracking occur in the contact area with impregnated graphite under the action of the high surface residual stress and the material oxidation and embrittlement induced by high temperatures, resulting in sealing failure.

In order to study the influence of frictional self-excited vibration of a pantograph-catenary system on the contact loss between the carbon strip and contact wire, a finite element model of the pantograph-catenary system at the rigid and flexible transition section of a metro was established based on the theory of frictional self-excited vibration. The complex eigenvalue analysis method was used to study the influence of different pantograph-catenary parameters on the frictional self-excited vibration of the system. The analysis results show that the main frequency of contact line corrugation caused by frictional self-excited vibration of the pantograph-catenary system is 399.61 Hz. When the friction coefficient is greater than or equal to 0.11, the pantograph-catenary system has unstable vibration, and with the increase in the friction coefficient, the unstable vibration tends to be stronger. The normal contact force, the contact position between the carbon strip and the contact wire, and the stiffness of the pantograph bow spring have great influences on the occurrence of the frictional self-excited vibration of the pantograph-catenary system. When the friction coefficient is less than 0.11, selecting the appropriate normal contact force or adjusting the stiffness of the pantograph bow spring can restrain or even eliminate the frictional self-excited vibration of the pantograph-catenary system and then reduce the contact loss caused by the friction between the pantograph and catenary.

The large eddy simulation (LES) method was applied to transiently simulate the wavy vortex field within the annular gap in Taylor-Couette and investigate the variation of fluctuations between wavy vortices. The wavy vortex field within the annulus gap was investigated from both two-dimensional and three-dimensional perspectives. The results indicate that the velocity vector field on the meridian plane of the two-dimensional wavy vortex field within the annular gap exhibits periodic fluctuation characteristics. The velocity vector field remains essentially the same at the beginning and end moments of the cycle. The axial velocity direction at the vortex junction changes constantly and periodically, while the radial and tangential velocity directions remain constant. The velocity values of the vortex pairs are greater than those of the vortex pairs inside the vortex, and the mainstream liquid transfer mainly occurs between the vortex pairs in the outward flow. Additionally, the fluctuation phenomenon of the three-dimensional wavy vortex field is clearly evident and exhibits periodic characteristics. The cycles for each working condition (10, 20, 30, and 40 r/min) are 12.94 seconds, 6.80 seconds, 1.93 seconds, and 1.49 seconds, respectively. With the increase in rotational Reynolds number, there is a significant decrease in vortex fluctuation amplitude and a reduction in the duration of fluctuations. The periodic flow transport of the mainstream liquid between vortices within the annulus gap propels fluid microclusters to perform a spiral-coupled vortex rotation around the inner cylinder within the annulus gap.

Finite element model simulation of the pantograph and overhead conductor rail (OCR) system is slow, and the time cost of calculation is high. Therefore, the simulation method and process of the pantograph and OCR system using three-dimensional contact formulation were improved. Firstly, the equation that needs to be calculated iteratively when solving the relative velocity of the contact pair between the pantograph and the OCR was replaced with an explicit equation that can be calculated directly based on the central difference method. Then, the OCR model was linearized at the static equilibrium state to avoid the time-consuming stiffness matrix assembly procedure and increase the efficiency when calculating the internal force of the OCR. Next, a lazy judgment strategy was used to estimate the contact state of the pantograph and the OCR to reduce the computational load. Finally, the computational efficiency and accuracy of the fast simulation method in different cases were analyzed. The results show that compared with the standard simulation method, the proposed fast simulation method can save 97.67% of computational time in the example of pantograph and OCR with 30 spans of 8 m, and the maximum error of contact force results is only 0.48%. With the increase in the model scale, the time saved by the fast simulation method increases sharply, and its computational efficiency advantage becomes more and more significant. Meanwhile, the errors of contact force results are all less than 1.00%. With the increase in the operation speed, the proportion of time saved by the fast simulation method remains stable, and the errors of contact force results increase slightly. At speeds under 230 km/h, the standard deviation errors of contact force are all less than 1.00%.

In the wide speed range of sensorless control, the traditional super-twisting second-order sliding mode observer algorithm had a problem that the error of rotor position estimation would change with the speed in the permanent magnet synchronous motor (PMSM). In order to improve the control performance of the motor speed and reduce the error of rotor position estimation, an improved sliding mode observer based on hyperbolic function was proposed, and an online identification scheme of stator resistance was designed. A disturbance voltage observer was designed to estimate the distortion voltage caused by the nonlinearity of the inverter on line. Finally, the hardware-in-the-loop test was carried out to verify the feasibility of the scheme. The test results show that the error of position estimation can be reduced by 7.6%, and the accuracy of velocity estimation can be increased by 5.8%.

For the compressive sensing algorithm, the correlation between measurement matrix and sparse base always determines the accuracy of signal recovery. In order to improve the performance of the compressive sensing algorithm in signal reconstruction in large-scale communication scenarios, the measurement matrix was improved based on matrix decomposition and equiangular tight frame (ETF) theory. Firstly, a dictionary matrix was constructed based on the measurement matrix and sparse base, and a Gram matrix was constructed. Eigenvalue decomposition was used to reduce the average correlation of the Gram matrix. Then, based on the ETF theory and gradient reduction theory, the Gram matrix was pushed to approach the ETF matrix to reduce the maximum value of the non-principal diagonal elements of the Gram matrix and the maximum correlation between the measurement matrix and the sparse basis. The orthogonal matching pursuit (OMP) algorithm was used as the reconstruction algorithm for simulation and verification, and the simulation results show that after optimization, the correlation coefficient of the matrix is reduced by 40%–50%. In channel estimation and active user detection, the estimation error of active user number by the proposed algorithm is more than 50% lower than that by other optimization algorithms under high sparsity; compared with other matrices, the mean square error of channel estimation is improved by 3 dB, and the bit error rate performance is improved by 2 dB.

To meet the demand for 5G communication in tunnels and increase the utilization rate of trackside antennas, a dual-band trackside antenna based on metamaterials was proposed, which could support both automatic train control systems and civil 5G wireless communication. First, a miniaturized dual-band trackside antenna was designed based on the 5G communication deployment scheme, and the finite element method was used to simulate the electromagnetic properties of the antenna before and after miniaturization. The impact on the electromagnetic environment and other radiation sources in the tunnel was evaluated. Second, a lightweight human body model containing important tissue such as the trunk, skull, brain, and heart was constructed, so as to compare the effects of radiation on the specific absorption rate (SAR) of human tissue between the simulated traditional single-band trackside antenna and the miniaturized dual-band trackside antenna. The results show that the miniaturized dual-band trackside antenna is 40% and 20% smaller than the traditional single-band trackside antenna when the antenna operates at 2.45 GHz and 3.40 GHz, respectively, and the electric field strength in the surrounding tunnel space is reduced by over 2.09% and 6.57%. The induced electric field strength on the leaky coaxial cable is reduced by 19.67% and 32.41%, respectively. The miniaturization of the antenna effectively reduces the impact on surrounding radiation sources and improves the electromagnetic compatibility of the trackside antenna inside the tunnel. The miniaturized dual-band trackside antenna makes the SAR values absorbed by the trunk, skull, brain, and heart of the human body drop by 19.76%, 46.60%, 55.62%, and 55.28%, respectively, which significantly decreases the radiation impact of the trackside antenna on occupational groups.

In order to improve the force performance and durability of assembled bridge piers, it was proposed to adopt the assembled bridge piers with hybrid connection of cast-in-place fiber-reinforced engineered cementitious composites (ECC) and assembled mortise and tenon joints and carry out the pseudo-static tests of the bridge piers with different design parameters (depth of the groove and thickness of the cast-in-place ECC layer), so as to establish the experimentally-validated ABAQUS finite-element model. In addition, extended parametric analysis was carried out, and theoretical derivation was conducted on the basis of the finite element parametric analysis. The calculation method of the eigenvalue of the skeleton curve and the restoring force model of the hybrid-connected assembled RC bridge pier were proposed. The results show that the damage mode of the three bridge pier specimens is compression bending damage, and the cast-in-place ECC section of each specimen is not damaged; the changes in the depth of the groove and the height of the cast-in-place ECC section have significant effects on the ductility coefficient and ultimate displacement of the bridge piers. The results of the theoretical analysis coincide with the results of the finite element analysis. The ratio of the calculated values of the formulas to the values of the finite element analysis ranges from 0.85 to 1.14, except for peak displacement, and the results are reliable; the hysteresis curve calculated by the hybrid-connected assembled bridge pier restoring force model matches well with the test curve, which can be used for the elastic-plastic calculation of bridge piers.

The intensifying global climate change is increasingly affecting the operational performance of existing transportation infrastructure due to extreme climatic events such as heavy precipitation, high temperatures, low temperatures, and drought, leading to severe damage. Meanwhile, with the further implementation of the strategy of building China with a strong transportation network, a significant number of new transportation infrastructure projects are being constructed in harsh environments, posing unprecedented challenges to the functionality, durability, and maintenance management of these new facilities. The characteristics of extreme climate loads include rapid and unpredictable variations, often accompanied by coupled effects of multiple disasters, rendering the mechanisms of damage to transportation infrastructure under their influence highly complex. To ensure the safety and effectiveness of transportation infrastructure under extreme climatic conditions, Chinese and international research on extreme climate and multi-disaster coupling was studied, and the research progress on spatiotemporal evolution of extreme climates and multi-disaster coupling effects was systematically reviewed. The impact mechanisms of multiple disasters on engineering structures were sorted out. Based on this foundation, the characteristics of extreme climate impacts were defined, and disaster prevention and reduction design principles for transportation infrastructure during the design, construction, and maintenance phases were proposed. Furthermore, methods for assessing multi-disaster risks to transportation infrastructure under extreme climatic conditions were comprehensively summarized, and future research was prospected, highlighting the importance of utilizing artificial intelligence and machine learning technologies for rapid prediction and assessment of extreme climatic disasters and analyzing changes in the performance of transportation infrastructure systems throughout their whole life cycle. This research provides valuable references for the disaster-resistant design, performance assessment, and resilience enhancement of transportation infrastructure such as bridges, roads, and tunnels under extreme climatic conditions.

In bridge health monitoring based on finite element models, Bayesian model updating techniques are commonly used to quantify the uncertainties of important parameters in the finite element models, so as to address the issue of non-uniqueness in model updating caused by measurement errors, modeling errors, computational errors, etc. To resolve the problem of low efficiency in model updating due to the large number of finite element simulations required, a Bayesian model updating method based on an adaptive nested sampling (ANS) algorithm was proposed. The method used the modal parameters to construct the probability objective function and adopted the ANS algorithm to approximate it. ANS retained the nature of nested sampling (NS), which made the samples ultimately approximate the optimal parameters by narrowing the sampling range layer by layer, and it simplified the computation process of the evidence value and the a posteriori probability density value by transforming the high-dimensional integration problem into a simple one-dimensional integration problem through layer-by-layer approximation. On this basis, the ANS algorithm could also reduce the call of the finite element model by adaptively adjusting the number of samples during the iteration process. Finally, a pedestrian truss bridge was used as a case study for Bayesian finite element model updating experiments. The results demonstrate that under the same algorithm parameter settings, the ANS algorithm reduces the number of finite element simulation calls by approximately 84% compared to the traditional NS algorithm. This leads to approximately 86% computational time savings while obtaining uncertainty updating results with equal accuracy.

The positioning and lowering construction of large prefabricated steel caissons for cross-sea bridges is facing significant threats from the complex marine environment, including extreme waves and currents. In-depth research on the dynamic characteristics of the steel caisson during the positioning and lowering process under wave and current effects is of great importance for the positioning accuracy, lowering stability, and construction safety of steel caissons. Based on the LS-DYNA finite element program, a three-dimensional full-scale steel caisson fluid-structure coupling model under the action of wave and current was established. By comparing with the second-order Stokes wave analytical solution and the experimental results of the existing flume coupling experiment, the accuracy of the three-dimensional fluid-structure coupling model was verified. Subsequently, the validated model was used to investigate the influence of wave parameters, flow parameters, anchor cable arrangement, and structure lowering position on the wave and current loads and dynamic characteristics during the positioning and lowering process of the steel caisson. The research results indicate that the proposed anchor cable arrangement can effectively reduce the displacement and inclination of the steel caisson structure under different wave and current conditions, with a maximum inclination angle of no more than 2°. Compared with the individual effect of currents, the maximum horizontal force, horizontal displacement, and inclination angle of the steel caisson caused by the combined effect of waves and currents are increased by at least about 86.34%, 25.15%, and 112.96%, respectively. As the submergence depth of the steel caisson increases, the maximum horizontal force and horizontal displacement experienced by the steel caisson increase by approximately 41.90% and 50.62%, respectively, while the maximum inclination angle of the steel caisson decreases by approximately 31.06%. In the study of the positioning and lowering process of the steel caisson, the influence of wave and current loads and displacements on the structure at different lowering depths should be fully considered, so as to provide a reliable theoretical basis for analyzing the stability of the steel caisson in the process of positioning and lowering.

Since it is difficult to accurately select representative super-high-dimensional random phase angles, the good lattice point with power generator method (GLPPGM) was utilized to generate samples of representative track irregularities, which were applied to the vehicle-bridge system to obtain the mean and standard deviation of random dynamic responses. Then, the calculation accuracy and efficiency of this method were explored by comparing the results of the pseudo-excitation method, deterministic time history method, and Monte Carlo method (MCM). Finally, the threshold value of the derailment factor considering the daily operation volume of trains was studied by using linear and nonlinear wheel-rail contact relationships. The Harmony train passing over a bridge was studied, and the results show that compared with that by the MCM, the uniformity between the samples of track irregularities generated by the GLPPGM in different directions is better. The probability characteristic parameters of the random dynamic response obtained by the GLPPGM have higher calculation accuracy than different methods, and its calculation efficiency is nearly five times higher than that of the MCM. When linear and nonlinear wheel-rail contact relationships are considered, the threshold value of the derailment factor differs by 4.68%, and the GLPPGM has a wider applicability.