Abstract:To study the design methods of regional hub-and-spoke freight network, 17 technical and economic indicators that reflect regional urban freight capacity were determined from three perspectives including social economy, transportation capacity, and transportation professionals. The principal component analysis was used to quantify the comprehensive freight competitiveness of each city and determine the set of hub cities in the region. Based on calculation results, speed and cost indexes were further introduced to improve gravity model and membership model, which can effectively quantify the freight attraction between regional cities, define the influencing range of the hub city, determine the subordination of the branch city, construct the regional urban transport corridor system, and thereby help to determine the regional hub-and-spoke freight network layout. By taking 18 cities in Henan province as an example, a freight network was constructed. Results show that the obtained hub-and-spoke freight network in Henan province was in accordance with real situations, which has Zhengzhou as the center and presents the spatial characteristics of “one ring, six hubs, and seven corridors”. Therefore, the proposed model is reasonable and can effectively guide the design and operation of regional hub-and-spoke freight network.

Abstract:To study the transfer characteristics of vehicle load on ballastless track, a vehicle-double-block ballastless track coupling dynamic model was established. The transfer law of dynamic stress and vibration acceleration of vehicle load in the ballastless track was investigated, and the influencing factors were analyzed, such as driving speed, structural size, and interlayer contact state. Results show that the main load-bearing area of the vehicle load was distributed in the bed slab, and the peak value of vertical dynamic stress was attenuated by 73% within the depth of 0.1 m. The main vibration area of the vehicle load was mainly distributed in the bed slab and transmitted to the supporting layer, and the peak value of vertical acceleration was attenuated by 89% within the depth of 0.1 m. The dynamic force and vibration response of the track structure both increased with increasing driving speed. When the width of the track structure was appropriately reduced, the force and vibration characteristics were less affected. By inserting the isolation layer between the structural layers, the dynamic response of the wheel-rail and the dynamic force of the track structure were reduced, but the vertical acceleration between the structural layers was obviously increased. Inserting the elastic layer could reduce the vertical acceleration of the rail, but the dynamic response of the wheel-rail and the stress and vibration characteristics of the bed slab and supporting layer were less affected. The results can provide theoretical reference for the design and optimization of ballastless track.

Abstract:The simplification of numerical simulation and model design of truss stiffening girder of suspension bridge is widely concerned. Based on the results of dynamic characteristics analysis of truss stiffening girder, by adopting the principle of equal fundamental frequencies of vertical bending, horizontal bending, and torsion, a simplified method was proposed for the calculation of equivalent mass moment of inertia, equivalent bending stiffness, and equivalent torsional stiffness of uniform section Euler beam under different boundary conditions (cantilever and two-end fixed types). The method was applied to the equivalent analysis of a plate-truss stiffening girder suspension bridge with main span of 576 m. Results show that the dynamic equivalent method was effective. All methods based on equivalent Euler beam had the disadvantage of not considering the shear performance of truss girder. Longer truss girder was closer to pure bending Euler beam, and truss girder of cantilever type was closer to Euler beam than two-end fixed truss girder. It is suggested to select longer delicate truss girder and cantilever boundary condition for the calculation of equivalent Euler beam of truss girder in suspension bridge.

Abstract:To study the workability of epoxy adhesive used as bonding layer in steel-concrete composite deck, a steel deck with pavement casted by unreinforced ultra-high performance concrete was chosen as research object, and an epoxy layer was introduced to connect the two materials. In the process of adhesive applying, the situation of poor pretreatment of steel surface was considered. A static test was conducted to evaluate the cohesive shear strength of the steel-concrete composite joint, and a full-scale deck specimen adopting the same adhesive bonding method was designed and tested under bending loads. The mechanical behaviors of the specimen were investigated, which include deflection of specimen, strain at different positions, and ultimate bearing capacity. The failure modes of the bonding layer were recoded, and the strain of the bonding layer before failure was analyzed by finite element method. Results show that epoxy adhesive was convenient for construction as a bonding layer between unreinforced rigid pavement and steel deck, and surface pretreatment of steel had influence on the bonding strength. The epoxy bonding ensured a reliable connection between the steel deck and the rigid pavement even with a poor pretreatment of the steel surface. Steel yielding occurred prior to the cohesive failure between the steel and the concrete. In addition, the bonding layer had a non-uniform shear stress distribution that the stress at the rib-to-deck joint was higher than other positions. The steel deck with adhesively bonded rigid pavement exhibited good ductility and high bearing capacity.

Abstract:To solve the problem that the overall traffic efficiency between adjacent intersections is difficult to be further improved due to the conflict of the optimal traffic efficiency between adjacent intersections in self-organizing control under urban traffic signals, a tuning method for parameters of self-organizing control rules under urban cellular network was proposed. First, the urban road network cell transmission model (CTM) was adopted to simulate the dynamic state information of the traffic flow on the road network. Then, based on the real-time information from CTM, the self-organizing control rule parameters of each intersection cell in the selected local road network were obtained for design space. Lastly, with the goal of maximizing traffic volume under the coordination of each intersection, the tuning of the self-organizing control rules of each intersection was completed. Simulation results show that under real-time information conditions, the tuning method based on urban cellular road network can not only solve the problem of the restriction of the traffic efficiency between local self-organized control intersections, but also effectively improve the traffic efficiency of the self-organizing adjacent intersections. The method provides an intelligent approach and an engineering theory for real-time urban traffic signal self-organizing control system in complex urban road network.

Abstract:To achieve a balance between force and displacement of bridges under earthquakes, a buffer cable sliding friction aseismic bearing (BCSFAB) was proposed on the basis of cable sliding friction aseismic bearing (CSFAB). The concept and the working mechanism of BCSFAB were introduced. A quasi-static test was carried out on CSFAB and BCSFAB, and test results were compared. Then, the numerical simulation method for BCSFAB was proposed and validated. Finally, by taking a continuous girder bridge as the research object, the seismic performance of BCSFAB and CSFAB under three near-field pulse-type waves was analyzed respectively. Results show that compared with CSFAB, BCSFAB performed better in reducing the peak displacement of bearing, maximum bending of pier bottom, and residual displacement of the structure, which has better limiting ability and self-centering capacity.

Abstract:To solve the problem that the current standard and specification cannot evaluate the skid resistance property of the asphalt roadways in use, a long-term skid resistance property evaluation index of asphalt mixture was proposed on the basis of the self-developed “thermo-control and accelerated wheel tracking polishing device” and the principle of differential polishing. Based on the differences of mineral contents, polished stone value(PSV), and microtextures of different aggregates, the optimum design of mixture proportion of stone mastic asphalt (SMA) was carried out by blending coarse and fine aggregates. Results show that the long-term skid resistance property of the SMA roadway was significantly improved (up to 5 BPN). For regions where high quality aggregates are scarce, by blending coarse aggregates of high and low PSV, the construction cost can be reduced and the long-term skid resistance property of the asphalt roadways can be significantly improved.

Abstract:To quantitatively analyze the interaction between vehicles in traffic flow, the vehicle interaction velocity-changing model of arterial road was studied. The concept of potential field influence region was defined through the analogy of gravitation and repulsion in the potential field theory. The attraction and repulsion between the target vehicle and the surrounding vehicles were attributed to the changes of the interaction area affected by the potential field. A vehicle interaction analysis method considering the influence area of potential field was proposed, and a linear model of the interaction area between target vehicle velocity variation and potential field was established. Vehicle coordinates and speed data collected by the P3-DT BeiDou high-precision positioning direction finder were used to calibrate model parameters. The speed changes of the target vehicle were calculated by the proposed method and compared with the measured data. Results show that the error values between the calculation results and the measured data were less than 15%. When the lane-changing time became shorter, the interaction between the lane-changing vehicle and the rear vehicle on the target lane was stronger, and the deceleration of the rear vehicle was operated more quickly, which verifies the validity of the model. The model normalizes the vehicle speed and spacing in traditional microscopic traffic flow analysis into the interaction area of potential field, which can provide method for the study of multi-vehicle interactions in microscopic traffic flow and speed control strategy for automatic driving vehicles.

Abstract:Taking into account the influence of saddle on the length of main cable and considering the convenience of operation as well as the calculation accuracy, an analytical calculation method for the length of main cable at the saddle of long-span suspension bridge was proposed. First, according to the geometric relationship between the main cable and the saddle, the main cable curve correction algorithm was derived. Then, the Newton-Raphson iterative method was used to solve the obtained binary nonlinear equations. Finally, the reliability of the method was verified using main cable saddle and loose cable saddle as examples. Results show that compared with traditional algorithm, six equations and six initial input parameters were reduced, which made the expression form clearer. Only two parameters were needed to be input and there was no strict requirement for the setting of the initial values of the parameters, which led to fast convergence and thus enhanced the operability. The number of iterations was reduced by 50%, and the calculation time was less than 10% of the traditional algorithm, which greatly improved the calculation efficiency and met the engineering requirements. The algorithm proposed in this paper can be easily applied to the determination of the length of main cable curve and the position of cable saddle during construction, which can make the construction control of the long-span suspension bridge more accurate so as to ensure that the state of the accomplished bridge meets the design requirements.

Abstract:To study the actual response behavior of asphalt pavement structure in a wide temperature range, a semi-rigid base asphalt pavement and a full-thickness asphalt pavement were selected as research objects and Falling Weight Deflectometer (FWD) as test load based on the RIOHTrack full-scale test track, and the service temperature and structure response of the two kinds of pavement structures were observed synchronously in the year of 2017. The basic rule of asphalt pavement structure response in wide temperature range was obtained, the relationship models between temperature and deflection, temperature and strain, and temperature and stress were established, and the distribution characteristics of strain and stress along the depth direction of the structures were analyzed. Results show that temperature had significant effect on deflection, strain, and stress response. With seasonal variation, the response values of the asphalt pavement structures in wide temperature range changed alternately with annual cycle, and the values were small in winter and large in summer. Exponential function model can be used to describe the correlation between temperature and structural response parameters, and the decision coefficient R² could reach more than 0.95 with good correlation. Within the wide temperature range, in addition to the monotonous increase or decrease of the strain or stress values inside the structure, temperature variation could also change the strain direction. In pavement structure calculation, it is suggested to select temperature at the most unfavorable season to check the stress state of the asphalt concrete layer in order to ensure the safety of the structure.

Abstract:For the microscopic analysis of road traffic conflicts in confluence sections of highway construction area and to explore the application of traffic conflict technology in the field of unmanned driving, 12 variables of microscopic traffic information were collected as training set. The Bayesian network model was established combined with prior knowledge, and the precision of the model was evaluated by using cross validation method. Results show that large vehicles, as the main body of the conflict, could lead to the increase of the probability and severity of traffic conflicts. The preceding and following vehicles of two conflict vehicles had certain impact on the collision between the two vehicles. Overtaking behavior increased the probability of traffic conflicts. The probability and severity of traffic conflicts were higher in ramp merging sections than in turning sections. The proposed Bayesian network traffic conflict model was used to evaluate driving strategies, and conflict avoidance measures were put forward, such as diverging large vehicles. In certain road sections, it is suggested to take control measures to prohibit overtaking, limit the length of a single lane, set up distance confirmation facilities, and so on.

Abstract:To study the effect of vehicle fire on the structural performance of long-span steel trussed arch bridge, a down-supported steel trussed arch bridge with main span of 240 m was taken as the research object for analysis and calculation. First, fire dynamic simulation (FDS) was utilized to simulate the fire temperature field distribution of two typical fire scenarios. Then, the temperature distribution inside the steel member was obtained by finite element instantaneous heat analysis. Finally, the ABAQUS thermal-structural coupling was used to analyze the structural performance variation of the bridge in different fire scenarios. Results show that the highest temperature of the steel arch rib members under the effect of tanker fire was up to 540 ℃. The main load transmitting member yielded at the temperature of 430 ℃, which reached the ultimate limit state, and thermal expansion and internal force redistribution led to the stress increase of the member in the fire area up to 60-180 MPa. The maximum variation of the vertical displacement of the bridge deck was 115 mm, and the maximum lateral height difference of the deck was 108 mm. The oil tanker fire mainly affected the temperature field of the three hanger rods near the fire area. Due to the reduction of the hanger rod force in the fire, the down deflection of the bridge deck was 33 mm and the stress of the main girder increased by 35 MPa.

Abstract:To analyze the influence of concrete damage on FRP confined concrete, 264 test data was collected from published literature, and a large database was established, which contains cross-sectional shapes, damage types, and damage levels of specimens, and FRP confined stiffness. Based on the database, the existing lateral strain-axial strain relationship models were evaluated, and a new lateral strain-axial strain relationship model of FRP confined pre-damage concrete columns was established by modifying Jiang’s model. Results show that Jiang’s model could accurately describe the lateral strain-axial strain behavior of FRP confined undamaged circular concrete columns, but the existing models were not suitable for FRP confined damage concrete columns. With the increase of concrete damage level, the deviation between the calculated value and the test value of the existing models increased. The proposed model was verified by database and could predict the lateral strain-axial strain behavior of FRP confined damage concrete column with good accuracy, which can be applied to FRP confined high temperature damage concrete columns. The model in this paper can be used for FRP confined pre-damage circular, square, and rectangular concrete columns as well as for the calculation of FRP confined preloading concrete columns and square columns.

Abstract:In view of the limitations of the current calculation methods for thermal stress and low temperature critical cracking temperature of asphalt binder and in order to find a better method for calculating thermal stress and corresponding low temperature critical cracking temperature of asphalt binder, the 70^# matrix asphalt of four different origins was selected for rotating thin film oven (RTFO) and pressure aging vessel (PAV) tests. The creep compliance of the asphalt binder was obtained by BBR test. The thermal stress of the asphalt were obtained by two-step calculation method of Hopkins & Hamming algorithm and CAM model as well as one-step calculation method of Laplace transform respectively, and the corresponding low temperature critical cracking temperature was calculated based on SAP theory. Calculation results were compared and analyzed by statistical methods. The calculation methods were verified by correlation analysis and combined with measured road surface temperature data. Results show that the one-step calculation method of Laplace transform and the two-step calculation method of Hopkins & Hamming algorithm were in good agreement. The calculation result of p-value of low temperature critical cracking temperature based on t-test was more than 0.90. The Laplace transform one-step calculation method had a strong correlation with the BBR test. The correlation coefficients between the critical cracking temperature T_CR and the S/m index as well as the Huet rheological model index reached 0.84 and 0.94, respectively. The calculation results of the measured road surface temperature change data prove that the proposed method is not only suitable for uniform cooling conditions, but also for on-site continuous variable speed cooling conditions at any cooling rate.

Abstract:In view of the problem of mass data compression generated during the diagnosis of metro vehicle plug door by PHM, a wavelet compression algorithm based on adaptive sectional threshold was proposed. Through the adaptive segmentation of the original data and the automatic adjustment of the amplification factor of the threshold of each segment, data compression with high accuracy and large compression ratio was achieved. To tackle the problems that the energy of the sampling current of the plug door motor was not concentrated and the amplitude varied greatly, the collected original data was adaptively segmented. Amplification factors of each segment of the wavelet threshold were adjusted automatically by a preset threshold, and then one-dimensional wavelet was used for data compression. On the premise of satisfying the accuracy of reconstructed signals, the method achieved high data compression ratio and greatly reduced the data amount to be stored. Data from Chaqiao Depot of Metro Line 2 in Wuxi, Jiangsu Province was obtained, and data compression test for metro vehicle plug door was carried out based on segmented adaptive wavelet threshold by selecting db3 wavelet for 4-layer wavelet compression. Results show that the test realized ultra-high compression ratio of 2.56% with the overall distortion ratio of 0.3%, indicating that the method is feasible and effective and can meet the requirements of actual engineering application.

Abstract:To improve the reliability of spacecraft system, an active fault tolerant control technique for spacecraft under the influence of disturbance was studied. First, in order to realize fault diagnosis under disturbance and reduce the time delay from fault detection to fault estimation, the concerned faults were extended to state vectors, and an unknown input observer was proposed for the integrated design of fault detection and fault estimation unit. Then, considering that the method needs to be further processed for interference estimation and can only solve the differentiable fault type, a novel adaptive sliding mode unknown input observer was designed, which can ensure the estimation of fault and disturbance decoupling at the same time and deal with a wider range of fault types. Finally, in view of the estimation error of the observer, a multivariable terminal sliding mode fault tolerant controller was proposed to improve its control performance. Simulation results show that the active fault tolerant control technique could realize fault diagnosis under the influence of disturbance and ensure the rapid recovery of control performance.

Abstract:To deal with the problems of low accuracy and poor generalization ability of high-power motor fault diagnosis in complex operation environment, a fault diagnosis method based on sound-vibration signal combined with one-dimensional convolutional neural network (1D-CNN) was proposed. First, a collected sound signal was denoised by the combination of background noise database and sparse representation. Next, the sound signal was filtered by band-pass filter (7-20 kHz), and low frequency vibration signal (within 7 kHz) was superimposed to form more complete motor state representation information in frequency band. Then, the information after filtering and purification was expanded by overlapping data to obtain a large amount of data required for 1D-CNN training. Finally, data samples were input into 1D-CNN for learning and training. Local response normalization (LRN) and kernel function decorrelation were used to improve the structure of 1D-CNN model, which reduced the impact of positive and negative half-cycle fluctuations of pumping unit on motor diagnostic accuracy. Diagnostic results show that the overall diagnostic accuracy of CNN fault diagnosis reached 97.75% based on combined sound and vibration signal analysis, and the generalization ability was good. Compared with traditional motor fault diagnosis methods, the proposed method had obvious advantages.

Abstract:To reduce the interference of corrosion electric field of ship on electromagnetic communication equipment, it is necessary to suppress or eliminate the corrosion electric field. A submarine corrosion electrostatic field model was established by using the three-dimensional boundary element method (3D-BEM) to investigate the influence of compensation anode positions on the electric field damping effect. The principle of electrostatic field damping was explained based on the electric dipole model theory, and the reasons for the difference in corrosion electric field of ship with different compensation anode positions were analyzed. Numerical simulation results show that the circumferential position of the compensation anode had little influence on the damping effect, while longitudinal position had significant influence on the damping effect. In addition, when the longitudinal distance between compensation anode and propeller was 16.6 m, 10.8 m, 5 m, and 1 m, the damping effect of the electric field modulus was 3.41%, 24.88%, 49.27%, and 34.15%, respectively.

Abstract:It is laborious and difficult to tune control gains in m-input m-output (MIMO) nonlinear systems using traditional decoupling algorithms, and the overall control performance is not good, so a self-decoupling control (SDC) method was proposed. The method utilized a linear extended state observer (LESO) to estimate and compensate the coupled part, nonlinear part, and disturbance part of the system, and an appropriate control law was designed for self-decoupling the MIMO system. The control gains to be tuned were converted into a parameter, and the convergence of the SDC method was verified by the Lyapunov method. Simulation results of two examples show that the proposed method not only greatly reduced the parameters of the MIMO system to be tuned, but also achieved better control effects than the common active disturbance rejection decoupling control method.

Abstract:To improve the dust collection efficiency of sweepers, the computational fluid dynamics method was applied to simulate the blowing-suction cleaning flow field. Influence of structural parameters on cleaning effect was analyzed combined with the gas-solid two-phase flow model. The multi-objective orthogonal test method based on weight matrix analysis was used to optimize the position parameters. Results show that when the width of the blow mouth was less than 0.93 of the width of the suction mouth, it is beneficial for improving cleaning efficiency with the increase of the width of the blow mouth. When the height of the blow mouth was more than 0.92 of the height of the suction mouth, the cleaning efficiency was improved with the increase of the height of the blow mouth, but the mean velocity near the ground and the outlet velocity of the blow mouth were reduced, which was not conducive to blowing up the dust. When the inclination of the blow mouth was 20°, the inclination of the suction mouth was 20°, the distance between the blow mouth and the suction mouth was 700 mm, and the height from the two mouths to the ground was 20 mm, the cleaning performance of the blowing-suction cleaning method was optimal. The airflow velocity was high near the ground in the blowing-suction cleaning flow field, where the airflow moved from the blow mouth to the suction mouth and the direction was close to the ground. There was no secondary pollution caused by the leakage of the airflow. The inclination of the blow mouth and the inclination of the suction mouth had the greatest influence on the cleaning performance, followed by the distance between the blow mouth and the suction mouth, and the height from the two mouths to the ground had the least effect.

Abstract:To study the effect of super hard asphalt (SHA) on high and low temperature rheological properties of SHA modified binders, SHA was adopted as modifier to modify AH-90 pavement petroleum asphalt. Different proportions (5%, 6%, 7%, and 8%) of SHA binders were prepared, and dynamic shear rheology test, multiple stress creep-recovery test, and bending beam rheometer test were carried out. Results show that SHA modified binder conformed to time-temperature equivalence principle. The addition of SHA significantly improved the rutting factor of asphalt binder, indicating that the high temperature performance of asphalt binder was obviously improved. With the increase of SHA content, the average strain recovery rate of asphalt binder increased gradually, and the unrecoverable creep compliance decreased gradually, which means SHA is conducive to improving the high-temperature deformation resistance ability and elastic resilience ability of asphalt binder. With the incorporation of SHA, the variations of creep stiffness and creep stiffness change rate of asphalt binder were small, and the low-temperature anti-cracking performance of asphalt binder was little affected. Modified asphalt binder with SHA had excellent rutting resistance at high temperature, and its low-temperature performance remained unchanged with respect to PG classification of matrix asphalt.

Abstract:To predict the recognition probability of traffic information at the intersection of interchanges, an approach using vehicle dynamics theory, driver characteristic principle, and dynamic traffic characteristics was adopted to obtain the recognition distance. On the basis of this approach, geometric and statistical principles were applied to establish a framework of traffic information within the recognition distance of typical automobiles. Furthermore, the traffic volume at the intersection of interchanges was predicted using short-and long-term time series, and the prediction results were subsequently implemented to form a prediction model for the recognition probability of traffic signs, which was validated with actual measurement. Results show that under long-term time series prediction, the traffic volume had a significant correlation with the traffic information recognition probability, and the correlation coefficient was 0.849. As for the short-term time series within a week, the overlapped area of 95% prediction interval band between the predicted value and the measured value reached 87.65%, which signifies a high reliability of the prediction model. Based on the high probability of traffic information recognition problems, for the intersection of interchanges with large traffic volume, consideration should be given to strengthen flexible traffic information settings and traffic control measures.

Abstract:In order to evaluate the reflective performance of colored pavement materials accurately, factors affecting the field measurement of albedo were tested by a double pyranometer outdoors, which include solar radiation intensity, height of pyranometer, incident angle, and surrounding conditions. A new albedometer for laboratory testing of albedo and internal temperature was developed to overcome the negative effects of field measurements. Six common colored pavement materials were tested and compared with cement concrete and asphalt mixture. Results show that solar incident intensity and incident angle had great influence on the field measurement of albedo. The greater the intensity and incident angle were, the greater the measured albedo was. The albedo of red, yellow, blue, and green pavement materials was 20%-25%, which was higher than that of open-graded asphalt mixture (5.8%), dense-graded asphalt mixture (5.4%), and porous cement concrete (16%), and slightly lower than that of dense cement concrete (32%). Under the same radiation conditions, the internal temperature of the colored pavement material was generally lower than that of asphalt mixture and porous cement concrete, whereas green pavement materials had the best cooling effect.

Abstract:To investigate the effects of load history on the bonding properties of carbon fiber reinforced polymer (CFRP) steel interface, long-term loading tests of CFRP-steel plate double-lap specimens were conducted under four interfacial shear stress levels and six types on loading time, and static tensile tests were carried out on the specimens which reached the specified loading time. Based on the axial strain data of CFRP, the distribution of interfacial shear stress and bond-slip curves were given. In view of the effect of interfacial creep damage on the bond-slip constitutive relations, coefficients β, η, and γ were introduced into bilinear model, and corresponding expressions were obtained by regression analysis. Results show that the creep deformation of the adhesive caused the redistribution of the interfacial stress. With the increase of time, the peak value of interfacial shear stress decreased and the strain of CFRP increased. After loading for 90 days, the interfacial shear stress of the specimens in groups B, C, D, and E at 12.5 mm decreased by 26.6%, 59.2%, 73.8%, and 85.4%, respectively. When the level of interfacial shear stress was high, the influence of interfacial creep damage on bond-slip curves should be considered, where higher interfacial shear stress and longer duration led to more significant creep damages. When the bonding length of CFRP was longer than the effective bonding length, the interfacial creep damage had no obvious effect on its ultimate bond strength.

Abstract:To study the mechanical properties of grouting body under microseismic loads, the grouting in red sandstone fissure with a fracture angle of 30° and a width of 4 mm was taken as the research object, and the uniaxial compression test was carried out by rock three-axis servo press at different strain rates (10^-5-5×10^-3 s^-1). Then, from the three aspects of energy principle, crack propagation mechanism, and final failure morphology, the influence law and mechanism of variable strain rate on the mechanical properties of grouting were analyzed. Research shows that with the increase of strain rate, the peak strength and elastic modulus of the grouting body increased, and the peak intensity and strain rate changed exponentially. The response of the grouting body affected by strain rate was divided into sensitive strain rate stage and slow strain rate stage, and the main difference was in the peak strength change rate and elastic modulus change rate. As the strain rate increased, the total energy of the grouting body increased. The compaction phase was the main phase affecting the mechanical properties of the grouting body under different strain rates. The main difference between the compaction phase in the sensitive strain rate stage and the slow strain rate stage was in the dispersion ratio, which further determined the number of cracks and the distribution area and its law. The dissipated energy density had a great influence on the failure area and the particle size distribution of the grouting body, where the greater the dissipated energy density was, the greater the proportion of large fragments was (the proportion of larger particle size increased gradually). The dissipated energy density in the slow strain rate stage was larger than that in the sensitive strain rate stage, so the fragments were larger than those in the sensitive strain rate stage. By analyzing the mechanical properties of the grouting in fractured zone under the influence of variable strain rate, the influence mechanism was obtained from the perspectives of energy theory and fractal theory.

Abstract:To guarantee the construction safety and traffic safety in the process of freeway reconstruction and extension, the setting of speed limit signs at the upstream of reconstruction and extension work zone was studied. Based on the analysis of the visual characteristics and braking characteristics of drivers in the process of driving in daytime and nighttime, the model of driver’s visual distance and the model of advance distance of speed limit sign were built, and a method for calculating the spacing of gradient speed limit signs at the upstream of work zone was proposed, which was then applied to the reconstruction and extension work zone in Jilin to Longjia Airport section of Huiwu Freeway. In the end, based on kinematics calculation method, the vehicle mean deceleration characteristics between different speed limit signs were obtained. Results show that with the increase of the values of speed limit, the spacing of adjacent speed limit signs in daytime and nighttime increased, which were positively linear correlated, and the spacing of speed limit signs in nighttime was greater than that in daytime. With the decrease of the values of speed limit, the mean deceleration of the vehicle in daytime and nighttime decreased, which were approximately in a positive linear correlation, and the mean deceleration in nighttime was less than that in daytime. The setting of spacing accorded with the psychological and physiological characteristics of drivers during the process of driving deceleration, which proves the rationality of the proposed calculation model for spacing.

Abstract:To solve the problem that the vertical negative effect of electric vehicles (EVs) is aggravated when added with in-wheel motor (IWM), the influence of different suspended configurations of IWM on vehicle vertical performance was studied under the coupling excitations of road excitation and motor vertical excitation. Effects of various configurations of EVs at home and abroad on ride comfort were comprehensively analyzed. The ride comfort of two schemes of IWM stator and whole motor suspended as dynamic absorber of vehicles was compared, and the computational model of dual excitations was built and used to select the optimal scheme. Then, by taking the minimum root mean square (RMS) value of vehicle ride comfort index as the optimization objective, NSGA-II algorithm was applied to optimize the stiffness and damping of rubber bushing of dynamic vibration absorber in the optimal scheme, and suitable configuration and matching parameters were obtained. At last, the optimized vehicle configuration was verified by simulation. Results show that the proposed two suspended schemes both alleviated the negative effects, while after the optimization of the selected whole motor suspended scheme, the acceleration of the vehicle body and the dynamic load of the tyre were reduced by 38.53% and 7.94% respectively. Simulation results verify that the optimized configuration and parameters under dual excitations reduced the vertical negative effect of EV driven by IWM and improved the vehicle ride comfort and safety.