The magnetorheological (MR) damper has attracted an increasing amount of attention in the field of vibration control because of its excellent adjustable damping performance. A modified model based on the modeling method of skeleton curve and hysteresis separation is proposed with sine and cosine magic formulas of MR damper in this study. The sobol sequence-based differential-tabu hybrid algorithm (SS-DTHA) is used to identify the parameters of the damping force model, and a general mathematical model including excitation characteristics and control current parameters is established. On the basis of test data and forward damper force model, the inverse model of MR damper control current is established by using adaptive-network-based fuzzy inference systems (ANFIS). The results show that the forward and inverse models established in this paper can better characterize the nonlinear behavior and hysteretic characteristics of the magnetorheological damper. The average percentage error of the improved magic formula model varies around 3.4% under different excitation characteristics and current conditions. The root means square (RMS) error of control current calculated by inverse dynamics model is 0.0869−0.1171 A. The RMS of error between the predicted damping force calculated by the control current inverse model and the damper forward model in series is 5.6% of the maximum damping force of the damper. Through the comparison of test data and simulation results, it is proved that the mathematical model of damper proposed in this paper has good accuracy and applicability, and can improve the vibration transmission characteristics of seat suspension system.

In order to create an identification method of aerodynamic noise source of high-speed trains, based on the wave equation of aeroacoustics, the high-speed train aerodynamic sound source was equivalent to countless micro-spherical sound sources. Using the relationship between sound radiation and physical quantities of the flow field, combined with the high-speed train aerodynamic numerical simulation technology, identification methods of dipole sound source and quadrupole sound source of high-speed train were established. The aerodynamic noise sources of a high-speed train head coach were identified from a new perspective by the methods. Based on the characteristics of the sound source term of the vortex sound equation, the relationship between the dipole sound source and the flow field was revealed. The research results clarify the strength and distribution characteristics of the main dipole and quadrupole sound sources of high-speed train, and indicate that the direct impact and separation of the airflow are the main reasons for the sound sources. The aerodynamic noise sources in the head coach and bogie area are mainly dipole sound sources. The strong dipole sound sources appear at the sharp edges of the parts. In most cases, the vorticity increases sharply when the fluid passes by those sharp edges, which becomes the main reason for the formation of a strong sound source.

With the increasing running speeds of high-speed trains, the problem of aerodynamic noise is gradually becoming more prominent. Determination of a method to predict the far-field aerodynamic noise of high-speed trains accurately and quickly has therefore become an important aim. The far-field acoustic integral formula for a half-model train is obtained in this work by solving the Ffowcs Williams and Hawkings （FW-H） equation using the Green’s function for semi-free space. A method is proposed to predict the far-field aerodynamic noise of a full-model high-speed train using the numerical calculation results for the half-model high-speed train’s aerodynamic noise. Numerical calculation models for the aerodynamic noise characteristics of high-speed trains are established with both the full model and the half model, and the aerodynamic noise sources on the surfaces of high-speed trains for the different models are solved using an improved delayed detached eddy simulation method. The numerical simulation calculation method used for the full-model high-speed train is verified using wind tunnel tests. The flow field, aerodynamic noise source, and far-field aerodynamic noise characteristics of the full-model and half-model high-speed trains are compared and analyzed. The results show that the flow field, aerodynamic noise source, and far-field aerodynamic noise characteristics obtained from the numerical calculations of the half-model high-speed train are consistent with those of the full model. Using the half-model calculations, the degree of fluctuation of the surface pressure in the streamlined area of the tail car and the noise source radiation intensity will both be overestimated. The far-field noise average sound pressure level error of the full model predicted using the half model is less than 1 dBA. When compared with the full-model high-speed train, the number of grid calculations performed for the half model is halved.

The liftgate is generally installed and fixed to the vehicle body through hinges, lock pins, sealing and buffers, whose rigid body modes vibrations are coupled with the passenger acoustic cavity modes, which are the main cause of low frequency booming noise. In this paper, a one-dimensional plate-cavity coupled analytical model including liftgate vibration and passenger acoustic cavity is established, and the effect of the boundary constraints stiffness on panel vibration and sound pressure level in cavity is analytically studied and experimentally verified in real vehicles. The theoretical results show that the sound pressure amplitude in cavity increases along the direction away from the liftgate and reaches the maximum value at the bottom location. The amplitude at the peak frequency of panel’s surface velocity and sound pressure level in cavity decreases with decreasing of stiffness of constraints. In the frequency range of 20−30 Hz, the amplitude at the peak frequency of sound pressure level at front seat is 8 dB(A) higher than that at middle seat and rear seat, which validates the theoretical results. The coupling sound pressure in the passenger cabin decreases with the increase of the relative position of the lockpin and the decrease of the relative height of the buffers. When the lockpin is increased 2 mm towards the rear of the vehicle body or the relative height of bumpers is decreased 2 mm, the liftgate vibration velocity can be reduced by 0.002−0.003 m/s, and the sound pressure level of the front row can be reduced by 3.5−14.8 dB(A).

In order to characterize and quantify a person’s subjective perception of road impact sound, firstly, the acoustic time perception duration of the impact non-stationary noise signal of the speed bump condition was defined, and the acoustic time history was divided into the impact section, the peak section and the attenuation section according to the discernibility of the human ear. The main impact and multiple micro-impact feature information of the impact noise were extracted by the wavelet transforms, and the feature information was used to form the basic feature matrix for impact sound quality evaluation. Then, the frequency domain filter factor was defined by referring to the crest factor method, and the time-varying perceptual weighting coefficient was determined based on the sequence relation analysis method, and the time-frequency filter network was established to weight the basic feature matrix and establish the impact sound quality evaluation index. Finally, based on the test data of the impact noise of the actual vehicle driving through the speed bump, the sound quality index was calculated, and comparative verification was carried out. The results show that the correlation coefficient between the proposed time-frequency perception weighted evaluation index and subjective evaluation is 0.927 at 20 km/h and 0.922 at 30 km/h. When considering the road impact acoustic time history evaluation, the correlation coefficient between the classic sound quality evaluation index(characteristic frequency band time-varying loudness) and subjective evaluation is 0.933 at 20 km/h and 0.649 at 30 km/h. The proposed time-frequency perception weighted evaluation method has good applicability for the conditions of 20 km/h and 30 km/h.

The original energy decoupling method is not suited to flexible double-layer vibration isolation systems, and therefore a multi-degree of freedom model is developed to represent the flexible characteristics of the equipment and intermediate mass. Then, on the basis of the model, a generalized elastic force is proposed to decouple the flexible vibration isolation system. The decoupling method is then extended to the study of flexible structures. Finally, using a two-layer vibration isolation system of a powertrain as an example, the method is adopted to evaluate the decoupling performance of the elastic mode of the frame. Finally, a vibration test was used to verify the effectiveness of this method. The results show that after the primary vertical frequency of the powerpack decreases from 12 Hz to 8 Hz, all of the modal frequencies of the system are reduced by different extents. The first two order frequencies of the rigid body vibration modes decreased by 50.00% and 49.98%, respectively. The elastic modal frequency of the frame has a greater impact because of its lower natural frequency compared with that of the diesel generator set. The elastic modal frequency of the frame decreased by 8.32%, and that of the diesel generator set decreased by 0.80%. In the elastic vibration mode vibration of the frame, the proportion of the elastic vibration energy of the frame could increase by 14.88%, and the proportion of the rigid body vibration energy could be reduced by 90.64%. Reducing the vertical frequency of the first stage vibration isolation system can improve the vibration decoupling effect and reduce the vibration transmission.

To improve the deterioration of combustion in the cylinder of diesel engines due to insufficient supercharging pressure under low operating conditions, two-stage turbocharging is combined with sequential turbocharging technology. First, the matching calculation of two-stage sequential turbocharging and diesel engine is carried out through propulsion characteristic tests, and the turbocharger model is determined. Secondly, the combined operation curve of the supercharger and diesel engine is obtained by using GT-power software to verify the feasibility of the scheme. Finally, the bench test is carried out to analyze the influence of two-stage sequential turbocharging on diesel engine performance under propulsion and load characteristics. The test results show that with propulsion characteristics, single turbocharging (1TC mode) can effectively improve the combustion deterioration under the engine load of 0–50%. Under the engine load of 50%–100%, the twin turbocharging (2TC mode) can further increase the air-fuel ratio and improve the in-cylinder combustion; especially at 60% engine load, the fuel consumption rate is 8.08% lower than that of the original engine. The two-stage sequential turbocharging mode can achieve good matching of turbochargers at low speed and full torque as well as medium-high speed and high torque.

The dynamic transmission characteristics of different types of high-speed track inspection vehicles are different, which makes the evaluation results of vehicle body acceleration on the same railway line different. To solve the above problem, the convolutional neural network (CNN) is combined with the gated recurrent unit (GRU) to establish a dynamic response prediction model for multi-vehicle dynamic response, which predicts the vertical and lateral acceleration of each vehicle by inputting a number of measured track irregularities and vehicle speeds, and uses the maximum envelope of the predicted values of multi-vehicle acceleration as the basis for track state evaluation. The results show that the model with eight track irregularities and vehicle speed, such as longitudinal irregularity, horizontal irregularity, as input parameters has the best prediction performance, and the evaluation indices of vertical and lateral vehicle acceleration prediction are increased by 5%–13% and 25%–36%, respectively. The vehicle acceleration predicted by the CNN-GRU model is in good agreement with the measured results in both time domain and frequency domains, with the maximum correlation coefficient of 0.902. Compared with back propagation (BP) neural network, CNN-GRU improves the evaluation indices of vertical and lateral vehicle acceleration prediction by 36%–109% and 11%–167%, respectively. The application result in a section with poor track geometry state shows that four out of the six vehicle types reach the level Ⅰ or Ⅱ overrun of the vehicle vertical acceleration, and one vehicle type reaches the level Ⅰ overrun of the vehicle lateral acceleration, which improves the accuracy and consistency of the track state evaluation.

The disc cutters located at the front end of a full-section tunnel boring machine (TBM) play an important role in the rock breaking process. The influence of the cross-sectional profile of the disc cutter on the rock fragmentation is important to study, to improve the TBM tunneling efficiency in engineering practice. Here, a two-dimensional particle flow model for rock cutting is established. Aiming at the flat-tip and circular-tip cutters, which are commonly used in engineering, two kinds of rocks with different strengths are selected, and a fixed confining pressure of 10 MPa is applied to one of the rocks. Then the rock cutting simulation is carried out, and the correlation between the cutter profile shape and the rock fragmentation is studied by analyzing the results of specific energies, rock fragment volumes, cutting forces, and crack numbers. A reduced-scale rock cutting experiment is performed to verify the correctness of the conclusions obtained from the simulations. The simulation results show that the cutter profile has a significant influence on the rock cutting performance. The specific energy of the circular-tip cutter is lower than that of the flat-tip cutter under most rock strengths and confining pressure conditions. The average reduction in the specific energy is 19.8% because the cutting force of the circular-tip cutter is 32.6% lower than that of the flat-top cutter on average. This indicates that the circular-top cutter does less work when tunneling, even though the total volumes of rock fragments created by the two types of cutters are similar (the average difference is 7%). Therefore, the circular-top cutter consumes less energy to break the same volume of rock. In summary, of the two commonly used cutter profiles, the circular-tip cutter is preferred for hard rock and high confining pressure tunneling.

In order to fully exploit the complex spatial-temporal dynamic correlation of traffic flow and improve the accuracy of traffic flow prediction, a spatial attention mechanism and an dilated causal convolutional neural network are introduced. A traffic flow prediction model STACNN based on spatial-temporal attention convolutional neural network is proposed. Firstly, the gated temporal convolution network block constructed by dilated causal convolution and gating unit is used to obtain the nonlinear temporal dynamic correlation of traffic flow and avoid gradient disappearance or gradient explosion when training long-term sequences. Secondly, the spatial attention mechanism is used to automatically assign attention weights to the traffic sensor nodes in the road network, which can dynamically pay attention to the spatial relationship between non-adjacent nodes, and combine the graph convolutional neural network to extract the local spatial dynamic correlation of the road network. Then, the final traffic flow prediction result is obtained through the fully connected layer. Finally, a 60-minute traffic flow prediction experiment is carried out using two highway traffic datasets PEMSD4 and PEMSD8. The experimental results show that: compared with the spatio-temporal graph convolutional network (STGCN) model with good performance in the baseline model, the MAE (mean absolute error) value of the prediction results of the proposed STACNN model on the two datasets is improved by 2.79% and 1.18%, the MAPE (mean absolute percentage error) value increased by 1.00% and 0.46%, and the RMSE (root mean square error) value increased by 3.8% and 1.25%, respectively. In addition, introducing dilated causal convolutional neural network and spatial attention mechanism have positively contributed to extraction of spatial-temporal dynamic correlation features.

In order to study the evolution rule of heterogeneous traffic flow under the background of IOV （internet of vehicles）, the concept of relative entropy in introduced to quantitatively describe the orderliness of heterogeneous flow, and analyze the inner link among orderliness, market penetration rate of CAV （connected and autonomous vehicle）and the number of queues for CACC (cooperative adaptive cruise control). Then, it is deduced that the increase on the market penetration rate of CAV and decrease on the number of queues can improve the orderliness of heterogeneous flow. Second, two improved lane change strategies for CAVs are proposed, namely, conservative aggregation (CSA) and radical aggregation (RDA). Through the simulation test of cellular automata, the advantages and disadvantages of no aggregation (NOA), conventional aggregation (CVA), CSA, and RDA are compared in terms of traffic capacity, relative entropy and average queue length. Finally, the effect of different limits of minimum queue size on traffic capacity is analyzed with the lane change strategy of CSA. The results show that the use of lane change strategy can prompt the CACC collaborative queue in CAV and orderly heterogeneous flow. It improves traffic capacity in the density range from 20 to 95 veh/km. Compared with the NOA strategy, the CSA strategy increases the traffic capacity by 12.6%, and the RDA strategy by 14.0%. However, when the market penetration rate of CAV is 0.8, the maximum traffic capacity of the RDA strategy is reduced by 25.8%. According to the quantitative description of relative entropy for the aggregation degree of CAV in heterogeneous flow, four lane change strategies (NOA, CVA, CSA and RDA) increases the aggregation degree of CAV in turn. In the CSA strategy, when the minimum queue size of CACC takes 4 vehicles, the efficiency of traffic capacity is the optimal.

In order to realize the collaborative optimization of operation scheduling and resource allocation in molten iron transportation, based on the theory of the cumulative scheduling with constraint programming and lexicographic multi-objective optimization, a double-layer and multi-objective constraint optimization method is explored for the transportation scheduling of molten iron. Firstly, setting the highest turnover rate of molten iron tanks and the highest operation efficiency as two lexicographic objectives, the upper-level constraint optimization model is built for molten iron transportation operation. In the model, the constraints are involved, such as operation sequence, operation implementation logic, time limit of molten iron cooling, limited operation times of molten iron tank, resource capacity limit, and resource pool of the molten iron tanks. Secondly, with the highest resource utilization balance, the lower-level constrained optimization model is established for resource allocation in molten iron transportation, in which the uniqueness of operation implementation and resource capacity are taken as constraints. Finally, the hybrid algorithm of constraint propagation and multi-point constructive search is developed to solve the whole model iteratively. The case study shows that, the turnover rate target and transportation efficiency target obtained by the hybrid algorithm are 14.29% and 60.53% higher than those obtained by the basic depth first backtracking algorithm respectively. Compared with weighted and single objective models, lexicographical multi-objective model improves the efficiency and quality of solution by 20.3% and 11.11%, respectively.

To improve the accuracy of cumulative prospect theory in modeling travel mode choice, given the differences in individual attitudes toward time and costs, the time value function and time weight function of the original cumulative prospect theory model are optimized. Firstly, in view of the preference reversal under time pressure, the travel mode is divided into rigid travel and flexible travel, the form of the time value function under the rigid travel scenario is improved, and the value range of the attraction parameter in the time weight function is calculated according to the travel time characteristics, and the MA-CPT (mental accounting-cumulative prospect theory) model is constructed. Secondly, the values of discrimination and attractiveness parameters in the time weight function are calibrated according to empirical data. Finally, the MA-CPT model is calibrated and its goodness of fit is tested, and the hit rates of MA-CPT and CPT models are compared. The empirical analysis results show that the attraction parameter value of the time weight function is greater than 1.00 under the scenarios of rigid travel and one-way travel. The goodness of fit of the MA-CPT model under rigid travel and flexible travel scenarios are 0.17 and 0.18, respectively. Compared with the CPT model, the hit rate of the MA-CPT model under flexible travel and rigid travel scenarios has increased by 12.2% and 19.8%, respectively.

The fatigue life and relaxation life of bolts affect their service life. Under the joint action of fatigue and relaxation, the connection at the column base is deteriorating. In order to explore the influence of the relaxation of connecting bolts on the fatigue life of high-speed railway sound barrier, bolts with asymmetrical and symmetrical arrangements used for high-speed railway sound barrier at a train speed of 400 km/h are taken as the research objects, and the finite element models of column base bolts are established using ANSYS. The preload is applied by cooling method, positive and negative unit bending moment loads are applied to calculate the stress amplitude of the most unfavorable bolt at the column base under different preloads, and the fitting relationship between the stress amplitude and preload is proposed. Moreover, based on Midas, a whole model of noise barrier is established to analyze the dynamic response characteristics of the barrier structure at the train speed of 400 km/h. The bending moment time history results of column base bolts are extracted to compare the bolt life considering fatigue failure only and the bolt life considering relaxation and fatigue together. Results show that the bolt relaxation will reduce the preload and increase the bolt stress amplitude of bolt base models in both cases of asymmetrical and symmetrical arrangements. In the existing time history calculation of column base bolts, the fatigue life considering the combined effect of relaxation and fatigue is much lower than that only considering the fatigue effect. When the preload is reduced to 55% due to the relaxation, the fatigue effect will occur. The results can provide a reference for designers of connection structures to quantitatively evaluate the bolt life and the maintenance of bolts.

Taking the mountainous terrain of the long-span suspension bridge as a typical example, the mean wind characteristics at bridge site in the mountainous terrain of a funnel-shaped canyon are studied, which provide a basis for the wind resistance design of large-span bridges in the funnel-shaped canyon area. Firstly, a numerical model of the actual terrain is established and 24 cases with different wind directions are analyzed by Fluent. Then, the simulation results are compared with the measured data to verify the resonableness of the numerical simulation. Finally, simulation results are used to explore the influence of the bridge location at the funnel-shaped canyon on mean wind velocity, wind attack angle, wind direction angle in different flow directions, and to analyze the characteristics of wind velocity distribution with different attack angles and vertical wind profiles at different locations. The research results show that there is an obvious canyon wind acceleration effect at the bridge site. The topography of funnel-shaped canyon shows weak disturbance and high directivity to the wind attack angle and wind direction angle in different flow directions at the bridge site in funnel-shaped canyon area, and the wind attack angle and wind direction angle are −5°–0° and 25°–30°, respectively. The wind velocity in the funnel-shaped canyon is more sensitive to the change of the attack angle.

The shelter effect of the bridge tower brings a sudden change of aerodynamic load on road vehicles passing by. For a single-level rail-cum-road bridge with larger scale of bridge tower in the longitudinal direction, the variation of the aerodynamic load is more intense. To explore the aerodynamic characteristics of vehicles near the pylon area on a single-level rail-cum-road bridge, a 1/20 scale wind tunnel test model is built. Based on the optimized test system, the aerodynamic loads of road vehicles passing by the bridge tower are measured. The influence of lane location, the vehicle type, and the bridge tower type on the aerodynamic load is discussed. The results reveal that traveling on a closer lane to the tower increases the variation amplitude in side force coefficient and yawing moment coefficient, and the upward lift force is also larger; thus vehicles are prone to sideslip and lateral-deviation. The vehicle length has a significant impact on the aerodynamic characteristics of the vehicles passing by the bridge tower area. Vehicles with smaller length possess larger variations of side force coefficient, while vehicles with larger length possesses larger variations of rolling moment coefficient, yawing moment coefficient and pitching moment coefficient. Compared with the bridge tower with a rectangular section, the bridge tower with chamfer decreases the sudden variation of side force coefficient of a van by 43.7%, and decreases the sudden variation of side force coefficient and yawing moment coefficient of a track-trailer by 25.8% and 29.2%, respectively.

When an offshore streamlined box girder is close to the water surface, the aerodynamic performance is easily interfered by extreme wave boundary conditions. To investigate the aerodynamic performance of the streamlined box girder under interferences from extreme wave boundary, the extreme wave is simulated using solitary wave. Based on FLUENT software, a numerical model for the aerodynamic performance of the streamlined box girder under interferences from moving solitary wave boundary is established by layering mesh method. The model is validated and then used to study the interferences from the moving solitary wave boundary on the aerodynamic performance, including aerostatic force coefficients, vorticity magnitude field, and distributions of the mean and fluctuating pressure coefficients of the streamlined box girder, under different parameters of wave boundary moving speed, wind attack angle and bridge clearance. The analysis results show that the aerodynamic performance of the streamlined box girder under the interferences from different solitary wave boundary moving speeds is apparently different from that of no-wave case. With wave boundary moving forward, the direction of the shear layer at the windward corner changes significantly compared to that at the corner of bottom surface (8° wind attack angle) and the top corner of upper leeward surface (−8° wind attack angle). Under the interferences from the moving solitary wave boundary, the buffeting response of the girder will be strengthened with the increment of the magnitudes of wind attack angles.

Longitudinal cracks of concrete caused by frost heaving of grouting slurry and free water in ducts is a special damage of post-tensioned PC girders in alpine regions, which affects the safety, serviceability, and durability of the structures significantly. In order to study damage characteristics, borehole and anatomical detections were conducted on damaged girders. The finite element software ABAQUS was used to establish the nonlinear models of frost heaving. Frost heave analysis of grouting slurry and parametric analysis of free water were carried out to study frost heave effects quantitatively. Control indexes of the frost heave ratio of grouting slurry and the volume of free water were obtained. The results show that the frost heaving of grouting slurry and free water occurs successively after grouting the ducts of the post-tensioned PC structures in alpine region, causing concrete to be tensioned repeatedly and cracked along the longitudinal direction. The volume expansion ratio of grouting slurry needs to be controlled within 0.80%, and the maximum should not exceed 1.73%. The volume ratio of bleeding water should be controlled within 0.04%, and the maximum should not exceed 0.52%. Thus, the frost heaving risk of grouting slurry and free water in ducts can be reduced effectively.

The interlayer is the weak link of the ballastless track and the rainwater intrusion can aggravate the debonding damage. To study the distribution of hydrodynamic pressure in the interlayer crack of ballastless track under the high-speed train load, a planar calculational model is established, the effects of debonding depth and crack opening on the vertical displacement are analyzed, and a debonding depth close to that measured in the spot is determined. A ballastless track crack simulation device is designed to verify the effectiveness of the device under high frequency loading; based on this device, hydrodynamic pressure experiments on the interlayer debonding are carried out to investigate the effects of load frequency and crack opening on the hydrodynamic pressure. The results show that when the load frequency is 25 Hz and the amplitude is 1.1 kN, the maximum vertical relative displacement at the plate end of the simulation device is the same as the spot test results, indicating that the device can be used for interlayer hydrodynamic simulation; under the high frequency load, the water pressure in the interlayer debonding alternately changes positively and negatively, and the hydrodynamic pressure increases along the depth direction of the crack, with the maximum water pressure at the tip of the crack being 15.794 kPa. When the load frequency increases from 15 Hz to 25 Hz, the maximum hydrodynamic pressure increases from 1.646 kPa to 15.794 kPa, which is about 10 times greater. When the opening is increased from 8 mm to 14 mm, the maximum hydrodynamic pressure increases from 8.320 kPa to 15.794 kPa, which is about 2 times greater.

In order to promote the application of square concrete-filled double skin tube (SCFDST) columns with outer stainless steel tube in civil engineering, six groups of specimens with different outer tube thicknesses and different core concrete strength were tested under axial compression, and the failure modes, load–displacement curves, and load–strain curves were obtained. The influences of the width-to-thickness ratio of the stainless steel square tube, the strength of core concrete, and the restraint effect coefficient of stainless steel square tube on the ultimate bearing capacity of SCFDST short columns were further analyzed. Meanwhile, the influence of chamfer on the strength and ductility of specimens was discussed preliminarily, and the minimum thickness calculation method to avoid the inner tube buckling before the outer tube buckling was proposed. Finally, based on the test results and the data in the existing literature, a fitted formula for calculating the compressive capacity of SCFDST short columns was derived; the calculated results by the proposed method were compared with those by the simplified model in the literature and the main foreign specifications, to verify its effectiveness. The results show that with the width-to-thickness ratio decreasing from 34.9 to 20.9, the ultimate bearing capacity was increased by 98.5% on average. When the core concrete strength was increased from C40 to C60, the ultimate bearing capacity of the specimen was increased by 7.3% on average. Besides, the axial ultimate bearing capacity of SCFDST short columns increases linearly with the constraint effect coefficient. Compared with the simplified model in the literature, the formula obtained in this study can predict the bearing capacity of SCFDST short columns.

To investigate the influence of snowdrifts on the flow field above low-rise building roof, the distributions of flow field above six different low-rise building roofs with or without snowdrifts were systematically analyzed through particle image velocimetry (PIV) experiments in wind tunnel combined with large eddy simulation (LES), where the tested models with snowdrifts were obtained by 3D printing based on the results of blowing snow experiments. The results indicate that a typical separation bubble can be formed above the no-snow roof when the approaching flow is separated at the leading edge, in which the obvious inverse flow can be observed. However, when there are snowdrifts on the roof, the backflow near the roof is weakened or even disappeared, which remarkably accelerates the flow velocity near the roof, and the maximum speed increment is about 0.6. Concurrently, the distributions of streamlines for snowdrift cases are closer to the building surface and have a larger velocity gradient, and hence the vorticity is also increased. The further numerical research on the turbulent characteristic above the building roof based on LES indicates that the turbulent kinetic energy and turbulence shear stresses above the snowdrift roof are also significantly smaller than their counterparts above the no-snow roof. However, the snowdrift increases the mean and fluctuating wind pressures in the windward region of the roof, and the reduction ratio is about 15% and 20%, respectively. Through this study, the mechanism of wind and snow load on low-rise buildings can be further analyzed, which can provide a reference for the wind-and-snow resistant design of roof structures.

The horizontal slip layer in the hollow brick infilled wall can weaken the inclined bracing effect of the wall and effectively reduce the damage degree of the hollow brick infilled wall. In order to understand the out-of-plane stability of the frame hollow brick infilled wall with horizontal slip layers, the out-of-plane failure mode of the wall was analyzed. Based on the in-plane quasi-static test of the frame hollow brick infilled wall with horizontal slip layers, the finite element models of the hollow brick infilled wall with and without horizontal slip layers were established, and the out-of-plane numerical simulation analysis was carried out. Results show that the horizontal slip layer will reduce the integrity of the wall and weaken the constraining effect of the surrounding frame on the wall. Compared with the ordinary infilled wall without slip layer, the failure degree of the infilled wall with horizontal slip layer is increased; specifically, the out-of-plane displacement and stiffness degradation rate is increased, the out-of-plane cracking load is reduced by 43.1%, and the peak load is reduced by 22.2%. Under the action of multiple and rare earthquakes with different seismic fortification intensities, the out-of-plane bearing capacity of the infilled wall with horizontal slip layers is greater than that calculated according to the code, which meets the code requirements.

The mesh woven with high-strength steel wires are widely used in fields of shallow geological disasters of slope and military engineering protection. As there are many weaving process parameters that affect the in-plane mechanical properties of the mesh, a refined numerical analysis can provide a basis for optimizing the mesh preparation process to give full play to its mechanical properties. Based on ANSYS Mechanical module and theoretical study of the mechanical properties of the mesh, a nonlinear numerical analysis of the mechanical properties of the wire mesh in plane tension was carried out taking into consideration the nonlinear stress strengthening effect of the steel wire material, the anisotropy formed by the geometric structure of the mesh, and the contact and state nonlinearity caused by the weaving process at the connection nodes of the mesh. Results show that the variation trend of stress and strain of the mesh obtained by numerical calculation is basically consistent with that obtained by experiment. Compared with the experimental results, the error of the equivalent elastic model (stiffness) of the mesh obtained by numerical calculation is 10.6% in the Y direction and is 18.5% in the X direction. The errors of ultimate stress and ultimate strain obtained by the numerical calculation are 10.0% and 12.8% in the Y direction and are 0.7% and 18.3% in the X direction, respectively.

In order to reveal the precipitation mechanism of covered Karst caves, the influence of the shape and size of the cave body and the internal law under the limit equilibrium, a common ellipsoid soil cave in straight collapse is investigated and its mechanical model of precipitation-induced subsidence is constructed. The calculation formula of the cavity negative pressure for the soil cave is deduced according to Boyle-Maliot law, so as to obtain the expression of the stability coefficient for the soil cavecollapse, and the feasibility of the calculation formula is verified by comparison. Further, the internal relations among the physical and mechanical parameters of soil mass, precipitation parameters, the spatial shape and size of soil hole and the overburden soil thickness under the limit equilibrium are obtained. Utilizing a calculation example, the influence of groundwater precipitation parameters and the shape and size parameters of the soil cave, and the internal law analysis under the limit equilibrium state are carried out. It is pointed out that when the initial water level is higher than the cave top, the stability coefficient of soil cave collapse and groundwater drawdown show a “Z”-shaped change, and it is very easy to cause soil cave collapse the moment the falling stable water level falls over the vault. When the initial water level is in the cave body, they show a negative correlation with changes steep in the front and slow in the back, and the higher the initial water level in the cave, the greater the decline; when the initial water level is lower than the cave bottom, the effect of drawdown is very small. The influence of the ratio of the long and short half axes of the ellipsoid on the stability coefficient conforms to the pattern of the increasing function. The greater the eccentricity of the cross section, the more stable it is, while the circular sphere is the most unfavorable. There is a linear relationship between the arch height and the stability coefficient. The arching effect is significant when the arch height increases, and the soil hole is more stable. Under the limit equilibrium, when the initial water level is fixed, the drawdown is positively correlated with the thickness of the overburden layer, showing a trend of slow change before and steep change after; however, when the thickness of the overburden layer is fixed, the drawdown is negatively correlated with the initial water level. The greater the horizontal section eccentricity of the soil cave or the higher the arch height, the deeper the groundwater required to reach the limit equilibrium, which is characterized by the changes gentle front and steep back.

In order to analyze the influence of the short fiber filaments and fiber mesh reinforcement on the mechanical property and frost resistance of foamed lightweight soil, a series of tests including unconfined compression tests, flexural strength tests, dynamic triaxial tests, and freeze-thaw cycle tests were performed. The results showed that to improve the compressive strength of the foamed lightweight soil, the optimal length and content of the short glass fiber mixed into the foamed lightweight soil with a design wet density of 700 kg/m³ are 6 mm and 0.4%, respectively. After the foamed lightweight soil with the designed wet density ranging from 400 to 1 000 kg/m³ was reinforced using short glass fibers with length of 6 mm and content of 0.6%, their compressive strength, flexural strength, and dynamic stress threshold were significantly improved, with the minimum increases being 35.3%, 31.4% and 53.4%, respectively. When the foamed lightweight soil had been reinforced with short glass fibers with length of 6 mm and content of 0.6%, the freezing-thawing durability of the foamed lightweight soil with design wet densities of 400, 700 and 1 000 kg/m³ increased from 5 cycles to 10 cycles, 25 cycles to 50 cycles, and 125 cycles to more than 150 cycles, respectively. This indicates that the frost resistance of the foamed lightweight soil was significantly improved. To improve the flexural strength of the foamed lightweight soil, the effect of the reinforcement by the glass fiber mesh combined with short fiber filaments (0.4% in weight) was the best, the effect of the single glass fiber mesh reinforcement was the second, and the effect of the single glass fiber filament reinforcement was the worst. Additionally, the toughness of the foamed lightweight soil can be improved significantly by short glass fiber filament reinforcement, glass fiber mesh reinforcement, or glass fiber mesh combined with short glass fiber filament reinforcement.

In order to study the heat and mass transfer behavior of saline soil in western cold-arid regions, firstly unsaturated sulfate saline soil experienced unidirectional freezing tests with no pressure recharge. In addition, while the latent heat of crystallization, crystallization impedance and crystallization consumption are considered, a three-field coupling model of water-heat-salt for unsaturated sulfate saline soil is established. Finally, COMSOL Multi-physics is used to simulate the coupling model, the simulation results of which are then compared with the experimental data for analysis. The results show that the internal temperature of saline soils develops in three stages with the freezing time, gradually forming a temperature gradient of cold at the top and warm at the bottom. Driven by both temperature gradient and matrix suction, water and salt migrate to the freezing front position, and the water and salt contents reach peaks at the freezing front position, and compared with the initial values, the peak water content and salt content increase by 2.16% and 0.28%, respectively. The freezing front moves along the frozen temperature line, and forms a freezing front. The maximum freezing depth of soil column is about 15.5 cm.

Determining the dynamic response characteristics of a subgrade under tram traffic loads is a key technical prerequisite for the design of embedded rail roadbed structures. First, a tram-embedded track-soil subgrade coupling dynamics model is established by considering the articulation forms between the car bodies, track support conditions, and damping effect of the subgrade. Then, dynamics simulations are performed using the track irregularity PSD of the China railway (CR) as excitation. Finally, the vehicle load characteristics on the subgrade surface are analyzed and the probability distribution characteristics of the dynamic stress amplification factor and its decay law with depth are discussed. The results show that the dynamic stress amplitude on the embedded track subgrade surface is subject to a normal distribution resulting from random track irregularities. Under the conditions of a tram with an 11 t axle, a design speed of 100 km/h, and a 90% CR track spectrum, the dynamic stress amplification factor on the subgrade surface obeys a normal distribution N (1.008, 0.100²), the frequent dynamic factor with a 30% exceedance probability is 1.058, and the limit dynamic factor with a 99.9% guarantee rate is 1.308. Influenced by the damping of the subgrade material, the dynamic stress amplification factor decays linearly with depth, and when the damping increases, the decay trend accelerates. With increasing depth, the mean dynamic stress amplification factor gradually decreases, from the dynamic action increasing zone slightly greater than 1, and to the dynamic action weakening zone less than 1.