2021, Doi: 10.11908/j.issn.0253-374x.20334
Is there any difference or what difference is in fatigue life between high-cycle fatigue tests of steel structures at the loading with low， medium， and high frequencies has always been a question for experimenters to find an answer to. Comparative analysis of fatigue test data （including tests conducted by the authors of the present paper and other scholars） was performed for structural steel as well as weldment at loadings between low frequency （below 30Hz） and medium-high frequency （around 100Hz）. The effects of low and medium-high frequency loadings on fatigue life was investigated. The fatigue tests dealt with high strength steel Q460 and its butt-welded joints， as well as butt-welded joints of normal strength steel Q345. It was found that there was substantial difference in fatigue life between low and medium-high frequency loadings. The former had a longer fatigue life or higher fatigue strength than the latter， whether it was steel or butt-welded joints. The mechanism for this phenomenon was also explained. It is suggested that for engineering steel structures subjected to low frequency fatigue loadings， fatigue tests should be conducted using low frequency fatigue testing machine. It may significantly underestimate fatigue life if a fatigue testing machine with a frequency higher than low frequency is used.
2021, Doi: 10.11908/j.issn.0253-374x.20314
An assembled self-centering buckling-restrained brace （ASC-RBB） was proposed， and its working mechanism and hysteretic behavior were theoretically analyzed. Furthermore， finite element models were established to investigate the hysteretic behavior of ASC-BRB， and to study the influence of key structural parameters on its hysteretic performance. The results show that the theoretically-derived restoring force model can effectively describe the hysteretic characteristics of ASC-BRB， and the theoretical results are in good agreement with the finite element results. After the combined disc springs being fully compressed， the stiffness of ASC-BRB increases significantly， which can prevent the rapid increment of the stratified deformation and reduce the deformation concentration of structures under strong earthquakes. When designing ASC-BRB， the key structural parameters need to be appropriately selected so that the brace can exhibit an appreciable deformation capacity， energy dissipation， and self-centering ability， and effectively reduce the deformation concentration of structures under strong earthquakes.
2021, Doi: 10.11908/j.issn.0253-374x.20205
By conducting a high-temperature steady-state test study on TSZ410 ferritic stainless steel， the main mechanical performance indicators such as elastic modulus， nominal yield strength， tensile strength， and elongation were obtained. The Rasmussen model and Gardner model were compared and analyzed. Based on the Rasmussen model， the calculation formula for the high-temperature stainless steel material hardening index was proposed and the high temperature stress-strain constitutive relationship of TSZ410 stainless steel was established. Compared with Q235B， S30408 austenitic stainless steel and EN 1.4003 stainless steel， the law of the effect of temperature on its mechanical properties was revealed. The results indicate that the initial elastic modulus， the nominal yield strength， and the tensile strength of TSZ410 stainless steel decrease gradually with the increase of temperature， especially in the temperature segment of 400℃ to 700℃， and the rate of decline is most significant. When heating temperatures are equal to 700°C， the elastic modulus is reduced to 40% of the normal temperature elastic modulus， and the nominal yield strength and tensile strength are reduced to about 15% of the nominal yield strength and tensile strength at room temperature. At a high temperature， the strength loss of TSZ410 stainless steel is larger than that of Q235B， while the stiffness loss is obviously less than that of Q235B. At a temperature below 500 ℃， TSZ410 stainless steel strength loss is significantly less than S30408 austenitic stainless steel， but when the temperature is higher than 500 ℃， the opposite is true.
2021, Doi: 10.11908/j.issn.0253-374x.20261
A novel method to modify recycled aggregate concrete （RAC） by nano-silica， two steps modification of nano-silica， and cement slury， was proposed in this paper. The stress-strain curves of RACs under uniaxial compression which were modified by three different methods at different strain rates （10-5s-1， 10-3s-1， and 10-1s-1） were obtained by conducting dynamic uniaxial compression test to explore the distinction between the curves before and after modification （two steps modification by nano-silica and cement slury， combined modification by nano-silica and fly ash， pre-soaking modification by nano-silica）. The results show that the novel modification method proposed could effectively promote the mechanical properties of RAC. Under the quasi-static condition， the peak stress and elastic modulus were increased by 25.1% and 85.8%， respectively. The dynamic increase factors（DIF） of the peak stress and elastic modulus of the modified RAC was decreased while the DIF of peak strain was increased. Finally， the dynamic stress-strain model of modified RAC was proposed， and the comparison results indicate that the predicted curves were in good agreement with the experimental curves， which can provide references for the engineering design and applications.
2021, Doi: 10.11908/j.issn.0253-374x.20212
Without expansion joints and bearings， integral abutment bridges can avoid the disease of expansion joints and the impact on driving. Since the superstructure and the substructure at the abutment are poured together， the force of the superstructure of integral abutment bridge is affected by the substructure and the soil， the calculation requires comprehensive consideration of the superstructure and the substructure， and the calculation method is more complex. The author proposes a new idea to realize the verification and adjustment of the superstructure under different load combinations. In this paper， a two-span integral abutment bridge is used as a supporting project， the boundary conditions are extracted under representative working conditions through a solid finite element model and applied to the grillage model of the full bridge， then we can complete the calculation and design of the integral abutment bridge， the specific process is as follows： In the solid finite element model， establish a simplified "single beam + single pile" model， and use the "m" method to determine the stiffness of the soil spring to simulate the structure-soil interaction； calculate the axial force and the linear displacement at the centroid of the beam end under the overall heating condition， and the bending moment and angular displacement at the beam end under mid-span loading condition， then convert them into two linear springs with a certain distance， which are applied to the grillage model of the full bridge as a boundary condition. In the grillage model， the internal force and bearing capacity of the full bridge under various working conditions are obtained， then the design of the integral abutment bridge is completed. In non-rock foundations， when the structure-soil interaction is simulated by the "m" method， the feasibility of the simplification and the design method has been verified.
2021, Doi: 10.11908/j.issn.0253-374x.20294
In order to facilitate the development and application of the seismic fragility analysis of underground structures in China， this paper presents a review of recent advance in seismic fragility research of underground structures， the existing issues and future tendency of this research topic are also discussed. Firstly， the definition of seismic fragility is described. Then， the selection of damage measure and intensity measure， as well as the effect of uncertainties， are discussed respectively. Two most widely-used methods for the construction of fragility curves in underground structures are introduced later. Based on the different sources of analysis data for the fragility analysis， five common used seismic fragility analysis methods for underground structures were summarized， and their applicability are also presented. Finally， the existing issues and the future tendency of seismic fragility analysis of underground structures are discussed.
2021, Doi: 10.11908/j.issn.0253-374x.20274
As a new type of transportation， virtual rail train has brought into full play the characteristics of strong adaptability of road transportation and large capacity of rail train. It is found that the running line of the virtual rail train has produced serious permanent deformation. Therefore， this paper uses a decoupling method to extract the three-way contact force of the tire-rigid road interaction model and act on the viscoelastic asphalt finite element model， aiming at the virtual track train tires in the three driving states of constant speed， full braking and steering The dynamic response and permanent deformation of asphalt pavement are analyzed and studied. The research results show that the road surface shear force and permanent deformation both decrease with the increase of speed when driving at a constant speed. Among them， the road surface shear force at a running speed of 20km·h-1 increases by 65% respectively compared with that of 60km·h-1 （longitudinal range））， 54% （transverse range）； the permanent deformation of 20km·h-1 is about 50% larger than that of 60km·h-1. In the longitudinal range， the maximum shear force of full braking is 66% higher than that of the road surface driving at a constant speed， and 76% is increased along the road depth. Longitudinal permanent deformation increases by 93% （10.512 million times）， 99% （552.56 million times）， and 100% （105.12 million times） respectively when fully braking compared to when driving at a constant speed. The maximum road surface shear force and the maximum horizontal and vertical permanent deformation are located on the inner side of the steering when turning. The maximum value of shear force under constant speed driving， full braking， and turning is on the upper layer. The maximum value of constant speed driving and turning is 0.03m from the road surface， and the maximum value of full braking is 0.04m away from the road surface. From the perspective of controlling road shear and permanent deformation， the higher the train running speed， the better it is to reduce road damage.
2021, Doi: 10.11908/j.issn.0253-374x.20414
To study the dynamic response of the tunnel and soil when the subway train passes the transition section of the floating slab track， this paper proposed a semi-analytical ring layered element for the efficient calculation of the tunnel-saturated soil vibration in time domain. Taking into consideration of the train-track model， the coupled dynamic model of the train-floating slab track transition section-tunnel-soil system was finally established. The effects of the parameters of the floating slab transition section （i.e.， the length and the stiffness of the steel spring） on the tunnel acceleration， soil normal stress and pore water pressure were studied. The results show that the parameter design of the floating slab track transition section needs to focus the dynamic responses at the two positions of sudden changes in stiffness of the transition section. The scheme of the gradient in steel spring stiffness can reduce the three evaluation indexes of the dynamic response by 60%， 15% and 25% respectively.
2021, Doi: 10.11908/j.issn.0253-374x.20199
In order to analyze the sound field distribution of subway underground platform from wheel-rail rolling noise， a three-dimensional full-length acoustic model of platform was established based on the geometric acoustic method. The wheel-rail rolling noise while the train was passing was calculated using the finite element method and boundary element method and it worked as the source of the platform acoustic model. The sound field distribution and propagation characteristics of the platform from wheel-rail rolling noise were studied.Based on which， the noise reduction effect of using sound-absorbing materials was analyzed， including the laying positions and lengths of absorbing materials. The results show that with a train entering， the most notable regions of noise on the platform are at the train-arriving end and 6m away from the platform gate of the passing side in lateral， and the noise is gradually reduced along longitudinal and lateral. The effect of rolling noise on the train-leaving end is small. The noise on the platform is most remarkable when only one train pulls into the station. The A-weighted overall sound pressure level reaches 83.1dB （A）. Besides， the cases that sound-absorbing materials covered both on the vertical wall of the niche under platform and side wall opposite the platform alongside the track area can achieve a good noise reduction effect. The noise reduction at the platform train-arriving end can reach 2.9~5.3dB （A）. Moreover， the noise reduction at the platform train-arriving end can reach 6.1~7.9dB （A） with the sound-absorbing materials laying area extending into the tunnel about 10m， especially when the train is near the platform but still in the tunnel. But the effect will not be improved obviously if the laying length continues to be extended.
2021, Doi: 10.11908/j.issn.0253-374x.20196
In this paper， the causes of errors in household travel surveys were analyzed， the traditional weighted sample expansion model was introduced， and its limitations， especially the lack of unreported trip records were analyzed. Combining the advantages and characteristics of the research method using cellphone data on travel behaviors， a novel model of using cellphone data to expand the sample of household travel surveys and mining unreported trip records was proposed. A sample expansion model was designed including five steps， combining the household travel survey data， traffic operation monitoring data， and cellphone data. Based on the stationary point classification technology， a travel behavior distribution model based on cellphone data was established. The parameters of the model split model were calibrated based on the revealed preference data of household travel surveys. The difference between the results of the survey sample， the traditional weighted sample expansion model， and the proposed model was analyzed from the aspects of travel purpose composition， time of day， and travel distance distribution. The results show that the model proposed reveals the unreported trip record caused by false reports and omissions.
2021, Doi: 10.11908/j.issn.0253-374x.20364
This paper discussed the research status and development trend of the dynamical problem of start-up judder of vehicles. First， the transmission system model of vehicles was used as a simulation platform to reproduce the problem， which focuses on the components closely related to the start-up conditions， including clutch operating characteristics， friction characteristics， and engine models. Then， in view of the start-up judder， the research contents and methods of start-up judder mechanics were discussed from the perspective of experimental research， generation mechanism， and suppression measures. Finally， based on the existing research results and their deficiencies， the focuses and difficulties of the research on start-up judder were pointed out， which provides references and suggestions for further research.
2021, Doi: 10.11908/j.issn.0253-374x.20342
To solve the problems of low output efficiency and short life of single-stack fuel cell systems， the energy management strategy （EMS） and control strategy of the multi-stack fuel cell （MFC） system for vehicles were studied in this paper. A multi-level EMS was proposed， in which the first-level EMS adaptively distributed energy between the MFC system and the power battery system based on working conditions， and the second-level EMS used an objective optimization function that took into account efficiency and life to optimize the distribution of each power output of the stack. The results show that compared with the single-stack fuel cell system， the fuel economy of the MFC system can be increased by 4% and the life performance of the MFC system can also be improved.
2021, Doi: 10.11908/j.issn.0253-374x.19332
In order to evaluate the exterior design of vehicles in a relatively objective way， the method of using BP neural network is proposed to evaluate vehicle exterior design after analyzing theory of artificial neural network. Based on the advantages of BP neural network such as self-learning， self-organization， self-adaption and nonlinear dynamic processing， a BP neural network evaluation model for vehicle exterior design was established. Twenty vehicle samples were selected as learning samples， and eight vehicle samples were used as test samples. The training and verification of the example of BP network were conducted using MATLAB software. The simulation results show that BP neural network is an efficient and accurate method to evaluate vehicle exterior design.
2021, Doi: 10.11908/j.issn.0253-374x.20255
A lap simulation study was conducted taking Formula Racing of college students as the object. By comprehensively considering the relationship between ground clearance and yaw angle and the drag coefficient and lift coefficient， the influence of body attitude change on aerodynamic characteristics of formula racing was studied combining experiment with numerical simulation. First， the existing vehicle aerodynamic model was modified. Then， the Longge-Kuta method was used to simulate the lap speed of the speed integral， which was compared with the simulation results of the commercial software Optimumlap. The results show that the model based on the coupling relationship between aerodynamic parameters and body attitude can more accurately describe lap simulation. Besides， ignoring the effect of aerodynamic changes， the grip of the tire during cornering will be overestimated， and the acceleration performance without considering the load transfer will be underestimated， thus overestimating the effect of drag on lap speed. Moreover， considering the model of load transfer， different tracks are found to have different sensitivities to drag. The lap simulation model provides reference for improving the aerodynamic design of racing cars.
2021, Doi: 10.11908/j.issn.0253-374x.20243
In order to study the subjective and objective mapping evaluation model of harmony with traffic for autonomous vehicles， this paper takes the highway on-ramp as a research scenario. First， based on the interaction sample data of natural driving data， a mapping evaluation model is constructed with objective index data and subjective evaluation results as model inputs and outputs， and objective indexes include average driving speed， side velocity， TTC， relative side velocity， deceleration degree of critical traffic participant and so on. Then， the influence of data preprocessing method and neural network type on the evaluation effect is analyzed using the 2×2 cross-comparison test. The results show that the precision of the BP neural network model and the Dropout neural network model based on Min-Max scaling is 95.71% and 80.00% respectively， and the precision of the BP neural network model and the Dropout neural network model based on staircase-function normalization is 94.60% and 73.25% respectively. It can be seen that the evaluation effect of the model is good， and the objective index set can express the evaluation of experts on the harmony with traffic. In terms of modeling method， the performance of the mapping evaluation model based on BP neural network is better than that of the Dropout neural network model， which can get more accurate evaluation results. In terms of data preprocessing method， the Min-Max scaling method can eliminate the magnitude difference between the data and keep the difference of objective index data between different samples， which can improve the evaluation accuracy of the mapping evaluation model. Therefore， when the sample size is small， the evaluation effect of the mapping evaluation model based on Min-Max scaling and the BP neural network is better.
2021, Doi: 10.11908/j.issn.0253-374x.TY20001
Multiview models， as the name stipulates， are models capturing real-world system perceived from different points of view （perspectives）， typically engaging locally available features （attributes， input variables）. When considered together， a collection of multiview models has to be aggregated. Multiview models also arise in the presence of data with a massive number of variables when building a monolithic model involving all attributes is neither feasible nor computationally sound. In this paper， two categories of scenarios have been formulated and discussed by focusing on fuzzy rule-based architectures. An important task when building an aggregate of multiview models is to equip the overall global model with a sound measure of quality， by using which， one can efficiently assess the relevance of the individual results produced by the rule-based models. It is， therefore， advocated that the quality of the results can be quantified by an output information granule rather than a single numeric outcome. In the two scenarios outlined above， the results produced by a family of multiview models are aggregated with the use of the augmented principle of justifiable granularity-one of the fundamentals of Granular Computing. It is also advocated that the diversity of the results delivered by multiview models can be captured and quantified in the granular form of the produced result. The related optimization criterion along with the associated optimization process are discussed.
2021, Doi: 10.11908/j.issn.0253-374x.20346
Similarity measurement is of great significance in big data related applications. However， the traditional cosine similarity traversal calculation method has a poor accuracy and timeliness， which cannot provide an effective basis for the quality assessment of massive high-dimensional data. To improve the accuracy of similarity calculation， two types of cotangent similarity formulas with cotangent trigonometric function and data dimensional differences was constructed. Besides， a back-propagation（BP） neural network model approximating the similarity mapping relationship of datasets was established to reduce the time complexity. The experimental results demonstrate that the improved fast similarity calculation method has a good accuracy and timeliness. Moreover， it has a more significant performance improvement when applied to large-scale datasets.