Abstract:In order to meet the requirements of vehicle load modeling and analysis for the digital transformation of highway bridges, the characteristics of vehicle load are analyzed and summarized. Based on the classification method of the number and complexity of random factors, vehicle load models are divided into single parameter vehicle load model, vehicle load spectrum, random traffic load model and vehicle load theoretical model. Based on this classification, the characteristics, modeling methods, development status, existing problems and application prospects of various vehicle load models are discussed. The findings demonstrate that existing vehicle load modeling methods mostly rely on sampling analysis of unknown stochastic processes, which are often inefficient and limited, and the resulting load models are not universal. In practical applications, appropriate modeling methods should be selected based on the characteristics of single factor vehicle load models, vehicle load spectra, and random traffic load models to meet application requirements. The stochastic traffic flow model is currently the most comprehensive modeling description of vehicle loads, and its basic research direction focuses on covering more load parameters, clarifying the correlation between various parameters, and more efficient modeling methods. The development of vehicle load theoretical model is not mature, which is the main direction of further research on vehicle load. With the development of society, the establishment of universal and automatic vehicle load model has become the basic trend of model development.

Abstract:This study analyses the dispersion characteristics of guided waves in rails. The semi-analytical spectral element method is proposed, and the finite element model of guided wave propagation in rails is established. Firstly, the spectral element method was used to improve the traditional semi-analytical finite element method, and the characteristic equation of waveguide structure was obtained. Secondly, based on the characteristic equation, the dispersion curves of an aluminum plate were calculated, and the dispersion characteristics of guided waves were analyzed. By comparing with the analytical solution of the aluminum plate, the accuracy of semi-analytical spectral element method was verified. Subsequently, the guided wave simulation model of the rail was established, and the dispersion characteristics of the guided wave in the rail were investigated. Finally, guided wave experiment for the CHN60 rail was carried out by RITEC RAM-5000 SNAP nonlinear high-energy ultra-sonic wave experiment system. The experimental results show that the group velocity obtained by the proposed method is highly consistent with the group velocity measured by experiment, and the relative error is only 0.99%. Hence, the semi-analytical spectral element method has high accuracy and feasibility in the analysis of guided wave dispersion characteristics of the rails, which provides a theoretical basis for guided wave damage detection in rails.

Abstract:In order to further promote the application level of recycled concrete filled steel tube components in earthquake prone areas, 10 recycled aggregate concrete filled circular steel tubular long columns (RACSTC) were designed for low cycle reciprocating loading. The experiment considers axial compression ratio and steel pipe wall thickness as influencing parameters, and conducts in-depth research on the failure mechanism and hysteresis performance, skeleton curve and ductility coefficient, energy dissipation and secant stiffness degradation of RACSTC. The experimental results show that the hysteresis curve of RACSTC is full without any pinching or shrinking, and the skeleton curve goes through the elastic stage, elastic- plastic stage, and descent stage, with good ductility. The yield displacement angle and ultimate displacement angle meet the standard specifications. The equivalent viscous damping coefficient of RACSTC during the failure stage ranges from 0.49 to 1.07, indicating that they have good deformation performance and seismic resistance. The research results can provide guiding reference for the practical application of recycled concrete filled steel tube components.

Abstract:The influential factors, assessment method, and prediction method for the discrete characteristics of subway vibration source strength were investigated through discrete characteristic analysis. All-day vibration source strength was monitored at 52 typical test sections in subway tunnels under operational conditions in several Chinese cities. The discrete characteristics and main influential factors of the vibration source strength were analyzed. Based on these data, an MLP neural network prediction method was proposed to estimate the subway vibration source strength. The fluctuation amplitude of the measured maximum Z-weighted vibration level exceeds 20 dB. The number of trials employed significantly affects the stability of the assessed vibration source strength. The fluctuation amplitude is 4.5 dB and 2.2 dB for 5 and 20 trains pass-by events, whereas the value reduces to 0.3 dB when 100 trials are adopted. The out-of-roundness of wheels is the main factor that leads to the discreteness of measured vibration levels. Moreover, the proposed MLP neural network prediction method shows high accuracy in predicting the subway vibration source strength.

Abstract:The objective of this study is to investigate the mechanical behavior, energy dissipation characteristics, and acoustic emission (AE) signal features of rocks with cross- fractures during loading. Rock specimens with varying angles of cross-fractures were fabricated, and uniaxial compression tests coupled with AE monitoring were conducted to obtain mechanical parameters and AE characteristics, including ring counts and cumulative counts. The results indicate that cross-fractures significantly affect the stress-strain relationship and mechanical properties of rocks, particularly at fracture angles of 30° and 60°, where pronounced stress drops and localized damage phenomena occur. The analysis of energy dissipation reveals that during the compaction phase, rock absorbs and dissipates energy. In the elastic phase, energy is transformed into elastic strain energy. However, in the plastic phase, as micro-damage increases, the dissipated energy rises while the growth rate of elastic strain energy decelerates. The AE ring count is closely related to the dynamic trend of dissipated energy. The propagation of fractures and the concentration of local stress promote frequent AE events, simultaneously intensifying the internal energy dissipation of the rock and leading to a reduction in elastic strain energy. These findings provide a theoretical basis for the early warning of engineering disasters in fractured rocks within the field of civil engineering.

Abstract:In this paper, a calibration method for the 3D earth pressure cell in sand is introduced. Using two customized calibration cylinders, the influence of the calibration cylinder size, the box size of the earth pressure cells, the capacity and the buried depth on the calibration coefficient of the 3D earth pressure cells in sand and the sand characteristics of the 3D earth pressure cell involving loading and unloading are studied. The results show that: ① The size of the calibration cylinder and the depth of burial have a large impact on the calibration results, whereas for the same range of 3D earth pressure cell, the size of the base and the transducer diameter-tothickness ratio have a smaller impact on the calibration results; ② The hysteresis of the large capacity 3D earth pressure cell is smaller than that of the small capacity cells, and the large capacity cells should be preferentially selected for soil stress measurement. ③ The unloading curve of the 3D earth pressure cell can be normalized by the maximum stress and output voltage value before unloading, and the normalized unloading curves of the 3.0 MPa cell has a small distribution bandwidth for different unloading curves, and the exponential curve can be used for analysis of soil stress measurement.

Abstract:The development of high- speed rail cannot be separated from scientific transportation organization and management. Compared with developed countries such as Japan, Germany and France, China’s high-speed rail has a longer operating line, and the passenger flow characteristics and demands along the line vary greatly in terms of running speed, travel time, transportation price and service quality. Its transportation organization and management have unique features and world-class technical and development levels. By analyzing the characteristics and complex features of China’s high-speed rail operation management, and in combination with the main contradictions of China’s railway transportation, according to the problem-oriented and demand-driven principles, technical solutions and practices for China’s high-speed rail transportation organization are proposed. Analyzing the characteristic cases of innovation and practice in the transportation organization and management of the Yangtze River Delta high-speed rail, including the highlights of innovative breakthroughs such as optimizing transportation supply based on market demand and comprehensive solutions for the operation of busy trunk lines. Based on the operational development of high-speed railway in the Yangtze River Delta region, this paper outlines the trends in the development of China’s high-speed rail operational organization and management.

Abstract:To improve the running performance of heavy-haul trains, a running optimization method for heavyhaul trains based on improved sparrow search algorithm (SSA) was proposed, considering the use of circulating air braking for long downhill descent. The force analysis of each train section was carried out, the longitudinal dynamic model of the train was constructed, and the multi- objective optimization model of the train operation curve was established; the Circle chaotic map and line requirements were used to generate the initial population, and the adaptive inertial weight factor and the SSA improved by Lévy flight strategy were used to optimize the maneuvering strategy of the train in the long downhill area. The simulation results based on the actual data of the HXD1 heavy-haul train on the Daqin Line show that the improved SSA has a significant improvement effect on the key indicators of the train in the optimization strategy, such as safety, energy saving and punctuality. This study can provide some reference for the theory of circulating air braking operation of long downhill heavy-haul trains.

Abstract:In order to reveal the safety mechanism of higher speed trains on the bridge under crosswind, a highspeed train-bridge aerodynamic model was established using CFD software to calculate the aerodynamic loads on the train and bridge based on fluid dynamics and vehicle dynamics theories. Using the co-simulation technology of multibody dynamics software UM and finite element analysis software Ansys, a high-speed train-trackbridge system dynamic model was developed. The aerodynamic loads on the train and bridge were applied as external excitations and input into the train-track-bridge system dynamics model to simulate the entire operational process of high-speed trains on bridges under crosswind conditions. The study analyzed the impact of wind speed and train speed on the operational safety of higher-speed trains. The results show that under crosswind conditions, the lateral displacement of the train body, lateral wheelset force, vertical wheel-rail force, derailment coefficient, wheel load reduction rate, and lateral displacement at the mid-span of the bridge all increase significantly compared to no-wind conditions. When the wind speed is slower than12 m/s and the train speed is 350~400 km/ h, the safety indicators for train operation remain relatively low, and the lateral displacement at the bridge midspan shows moderate variation. When the wind speed is fast er than 15 m/s and the train speed is between 350~ 420 km/h, the safety indicators of the train increase sharply, especially for trains traveling at speeds above 400 km/h, where the lateral interaction between the wheel and rail becomes more pronounced, resulting in an exponential increase in the lateral displacement at the bridge mid-span. The above research results can provide a theoretical basis and basic data for ensuring the running safety of high-speed trains on bridges under the influence of crosswinds.

Abstract:In order to study the propagation characteristics of acoustic emission waves generated by damage in the switch rail of heavy-haul-railway, this article takes the switch rail of the No. 12 turnout on heavy haul railways as the research object. Combining Abaqus simulation and the lead-break acoustic emission experimental technique, it simulates the acoustic emission signal generated by the damage of the switch rail through the leadbreak experiment, conducts a detailed analysis of the acoustic emission simulation method of the turnout switch rail, verifies the correctness and effectiveness of the simulation model, and validates the simulation results through on-site measurements.The results show that the damage emission signals in different characteristic sections of the switch rail have similar frequency distribution characteristics. However, the intensity gradually decreases with the increase of the characteristic section. Moreover, with the continuous increase of the conduction distance, the energy disperses to other frequency bands in the wavelet time-frequency diagram. The introduction of the damage model increases the response of the acoustic emission signals in each frequency band, especially producing an abnormal peak between 160 and 200 kHz. This result has also been verified through on-site measurements.The research results can provide reference for the analysis and application of acoustic emission signals in the detection of switch rail damage.

Abstract:To investigate the tensile behavior and failure mechanism of carbon fiber reinforced polymer (CFRP) composites after fire exposure, tensile tests were conducted on three different layups of CFRP laminates subjected to fire exposure. Thermal stability was monitored using an infrared thermal imager, followed by microstructural analysis via SEM to investigate the effects of burn temperature and fiber lay-up on the pyrolysis behavior of CFRP laminates. Finally, their tensile strength and failure mechanisms were evaluated through load-displacement curves, stress-strain curves, and failure morphologies. The results show that CFRP laminates subjected to high-temperature exposure exhibit significant pyrolysis and mass loss, and their damage mechanisms include matrix decomposition, fiber/matrix interface debonding, and interlaminar delamination. Compared to 400 ℃, specimens exhibit a twofold increase in mass loss and more severe damage at 600 ℃. A similar trend in curves and a significant difference in strength are found in ±45° laminates, whose mechanical performance depends greatly on the resin properties and fiber/matrix adhesion. The ranking of tensile strength for specimens after fire exposure is as follows: 0° laminate, 0°/90° laminate, and ±45° laminate. Furthermore, the 0° laminate experiences the smallest degradation rate.

Abstract:In order to improve the meshing performance of harmonic gear in the transmission process, the double-circular-arc tooth profile without common tangent of the flexspline was designed, and the neutral layer curve equation of the flexspline and the accurate rotation angle relationship of the harmonic drive were established. Then, the conjugate circular spline tooth profile of the flexspline was solved based on the envelope method. Finally, the meshing characteristics of the designed tooth profile were analyzed by using MATLAB , including conjugate domain and conjugate tooth profile analysis, motion path analysis, assembly state analysis and simulation analysis. The meshing characteristics analysis results indicate that the conjugate interval of the designed tooth profiles is larger, the working arc length is longer, and the gap between tooth profiles is smaller, the number of teeth involved in meshing being larger with no interference between the tooth profiles. The meshing characteristics of the harmonic drive for the designed double-circular-arc tooth profile is good, which improves the loadbearing capacity and transmission accuracy of the harmonic drive and reduces the noise in the transmission process, thereby improving the performance of the harmonic drive.

Abstract:A fully smoothed finite element method to solve the torsion problem of axisymmetric elastic body is proposed. Due to axial symmetry of geometry and boundary conditions, computing the torsion problem of axisymmetric elastic body requires extracting one cross section for meshing and analysis. In order to address the problem of high sensitivity to mesh distortion, the edge-based smoothing domains are further constructed based on the triangular mesh and smoothing operations are performed on the strain in each smoothing domain. The smoothing strain technique is combined with the quasi-weak form of smoothed integral for treatment of the partial derivative and non-partial derivative of shape functions. Accordingly, all the smoothed domain integrals can be simplified as boundary integrals of the smoothing domains and there is no need for the coordinate mapping and calculation of Jacobian matrix. Numerical examples demonstrate that the proposed method for the torsion problems of axisymmetric elastic body can produce accurate solutions even for irregular elements.