Abstract:

In this paper， a systematic parametric study is conducted to investigate factors affecting the seismic performance of steel frame coupled with dual-rocking structure （DRF）. Design requirements are proposed based on the Chinese code for the seismic design of buildings. Firstly， a simplified analytical model for DRF is introduced and validated through elastic-plastic seismic response analysis. Subsequently， dimensionless parameters affecting the seismic response of DRF are identified and optimal value range is determined through parametric studies of the simplified analytical model. Finally， a seismic design procedure for DRF is proposed and validated through numerical examples. It is shown that the seismic performance of DRF under maximum considered earthquake is satisfactory. Rationally designed dual-rocking steel frames exhibit significantly reduced internal forces within structural components compared to single-rocking steel frames. When coupled with dampers， dual-rocking steel frames can suppress weak stories and mitigate seismic responses， demonstrating practical engineering feasibility.

Abstract:

The performance objective of reinforced concrete pylons of long-span bridges under the safety evaluation earthquake （SEE） is consistent at home and abroad； however， the specified performance limits used for the seismic design of pylons are quite different. The performance requirements at the ultimate limit state and the operational limit state of post-earthquake structures are analyzed， and then the specific performance indices for the seismic resilience design of post-earthquake structures are presented， including residual capacity， residual displacement， residual stiffness， and residual crack width. Based on the fourth Panama Canal Bridge， the four widely used performance limits， such as the first yield moment， effective yield moment， limited ductility of q=1.5， and limits of material strains， i.e.， steel tensile strain less than 0.01 and concrete compressive strain less than 0.004， are compared. It is shown that the difference between seismic intensities corresponding to the four performance limits is very large， even larger than that between SEE and the functional evaluation earthquake （FEE）. The four performance limits are further evaluated with the specific performance indices presented for the seismic resilience design of post-earthquake structures. The first yield moment， effective yield moment， and limited ductility of q=1.5 can well satisfy the performance objective of sustaining to full functionality after the shock with none or only simple rehabilitation. The currently used performance limit of effective yield moments for the seismic design of pylons under SEE seems too conservative and at least the limited ductility of q=1.5 could be used instead. Moreover， considering the stiffness degradation due to the seismic damage and its effect on the increase of displacement responses of expansion joints， bearings， and damping units， the performance limit of material strains， i.e.， steel tensile strain less than 0.01 and concrete compressive strain less than 0.004， could be employed.

Abstract:

A diffusion-convection governing equation for chloride transport was established based on the Fick’s second law and Darcy’s law. Variations of chloride profile and degree of water saturation during each wetting-drying cycle were obtained by using COMSOL Multiphysics software to numerically simulate the diffusion-convection process. Sensitivity of corrosion initiation time to different influencing factors was analyzed. The results indicate that the coupled effects of convection and diffusion lead to the existences of convection zone and peak chloride content. The peak chloride content significantly increases as the exposure duration increases. Convection effect only dominates the chloride transport in the shallow zone of concrete， the chloride transport in the deep zone is governed by diffusion. Corrosion initiation time is most sensitive to the variation of critical chloride content， followed by the concrete cover depth， chloride diffusion coefficient， convection zone depth and peak chloride content.

Abstract:

As the substructure of load-bearing bridge， the load-bearing performance of reinforced soil flexible abutment and its influencing factors have always been concerned. In this paper， a reinforced soil abutment on Tongyue Expressway is taken as a prototype， and four large scale model tests of reinforced soil abutment are completed. The effects of reinforcement spacing， the connection form between reinforcement and block panel， and the backfill gradation on the loading-bearing performance and deformation characteristics of the abutment are studied. The test results show that the reinforcement spacing and backfill gradation （including the maximum particle size） are important factors affecting the load-bearing capacity of reinforced soil abutment， and the connection form （strength） between reinforcement and block panel has an important effect on the deformation control of reinforced soil abutment. Reducing the reinforcement spacing and improving the backfill gradation can increase the overall stiffness of the reinforced soil composite， reduce the deformation of the abutment， and enhance the load-bearing capacity of the abutment. Compared with the friction connection between reinforcement and block panel， the mechanical connection limits the relative displacement of the reinforcement from block panel， and enhances the lateral constraint of the reinforced soil composite， reducing the deformation of the abutment.

Abstract:

In order to ensure the safety of adjacent subway tunnels during deep foundation pit excavation in Nanjing soft soil area， it is necessary to propose control indicators based on protection requirements of subway tunnels. Based on a deep foundation pit project in Nanjing， the effect of deep foundation pit excavation on the deformation of adjacent subway tunnels was studied through 3D finite element numerical simulation. The deformation response characteristics of subway tunnels and foundation pits under the condition of relative position changes were systematically explored， and a formula for calculating the maximum horizontal displacement of subway tunnels was put forward. According to protection requirements of subway tunnels， the impact area of foundation pit excavation on subway tunnels was divided， and then a control standard for the horizontal deformation of foundation pit enclosure based on subway tunnel protection requirements was proposed.

Abstract:

This study focuses on the issue of compressed air pressure escaping along the outlet direction of the screw conveyor， which makes it difficult to establish a stable air pressure within the pressure chamber. A gas-water-solid coupling calculation model for compressed air in the pressure chamber-screw conveyor system is developed based on Geostudio Air/w. The effect of compressed air under different air pressures， conditioned soil properties， and empty chamber heights of the shield pressure chamber on the air leakage rate at the screw conveyor outlet is analyzed. The results indicate that the conditioned soil water permeability coefficient and compressed air pressure in the chamber are the two main factors affecting the escape of compressed air in the pressure chamber. Soil conditioning can reduce the water permeability coefficient of conditioned soil， thereby increasing the auxiliary air pressure. When the water permeability coefficient is gradually reduced from 6×10?? m·s?1 to 6×10?? m·s?1， the pressure retention capacity increases linearly from 130 kPa to 240 kPa. When the water permeability coefficient is further reduced to less than 4×10?? m·s?1， the pressure retention capacity of the pressure chamber can reach 300 kPa. The internal structure of the screw conveyor can effectively reduce the escape of compressed air. The air leakage rate without considering the internal structural characteristics of the screw conveyor is seven times more than that when the structural characteristics are taken into account.

Abstract:

Laboratory tests on the deformation and resistivity characteristics of unsaturated compacted loess under dry-wet cycles were carried out. First， the volume deformation and resistivity characteristics during cycling， as well as surface cracks after the desiccation of the sample undergoing five dry-wet cycles were obtained. Then， compression properties of the sample with different water contents were studied by the constant rate of strain （CRS） method， and the resistivity was also obtained. Finally， the nuclear magnetic resonance imaging and scanning electron microscopy were used to study the microscopic characteristics of the sample. The results show that with the increase of the number of dry-wet cycles， the swelling stain and crack ratio of the sample increase and the resistivity decreases， all of them tend to be stable as well. The yield stress significantly decreases and the elastic and plastic compression indexes increase after three wet-dry cycles. With the increase of the number of dry-wet cycles， the number of small pores in the compacted unsaturated loess obviously increases and the number of medium and large pores has a slight variation.

Abstract:

Addressing the limitations of existing research， such as low precision in depicting dynamic traffic systems and insufficient consideration of interactions between flood points， this study presents a simulation-based optimization method for assessing urban flood mitigation priorities. By maximizing the average travel time of road network users as the objective and using flood-affected road sections as decision variables， a 0-1 programming problem is formulated to transform the priority assessment into a discrete optimization problem. The interactions between flood points are captured through the search for optimal mitigation point combinations. A mesoscopic traffic simulation tool， DynusT， is employed for detailed road network modeling， and a fast machine learning model is utilized as a surrogate to enable a closed-loop simulation optimization algorithm for determining mitigation priorities. The method is validated through a case study in the central urban area of Guangzhou. Results demonstrate that implementing mitigation measures based on the priority ranking improve the average travel speed by 28.72% compared to existing solutions， confirming the accuracy of the method .

Abstract:

In recent years， the research on intelligent trip chains for large comprehensive passenger transportation hubs based on utility theory has received extensive attention. Firstly，the utility model of hub passenger transportation was proposed. Based on data mining technology and user profiling technology， the travel demands of hub passengers were accurately identified. With the goal of optimizing passenger travel utility， a typical user priority filtering recommendation algorithm and an information dynamic update strategy were proposed. Secondly，for scenarios with large passenger flows， a transportation system utility model was established， and an intelligent trip chain based on the optimization of transportation system efficiency was proposed to balance various transportation modes. Thirdly，during the normal operation of the transportation system service， to avoid the resonance in the transportation system， a bi-level programming model for the equilibrium optimization of passenger and transportation system utility was established. Finally，verified by the internal test of the “Changxing Hongqiao” APP， after adopting the intelligent trip chain， the overall rate of change in transportation modes is approximately 0.050， the overall satisfaction score of the trip chain increases by 0.160， and the rate of change in travel time decreases by 0.056.

Abstract:

Aiming at the van-unmanned vehicle routing problem with simultaneous delivery and pick-up under time-dependent road network， a model is formulated to minimize the sum of dispatching costs， energy consumption cost and time windows penalty cost by comprehensively considering factors such as the delivery area road network traffic information， customer demand for simultaneous delivery and pick-up， customer soft time windows and battery state of charge. A hybrid genetic variable neighborhood search algorithm is designed. The algorithm uses a roulette selection strategy. The strategy of adaptive neighborhood search is introduced， and different search times are designed in different periods of the algorithm to accelerate the convergence speed of the algorithm and improve the solution quality. By solving multiple sets of instances， the correctness of the model and the effectiveness of the algorithm are verified. Sensitivity analysis is carried out on the changes of scenarios such as the cooperative distribution mode of different van-unmanned vehicles， the driving speed of different vans， and the combination of different minimum battery states of charge of vans and unmanned vehicles. The results show that the cooperative distribution mode of van not waiting for unmanned vehicles can effectively reduce the delivery cost； considering the time-varying speed of vans can better adapt to different road conditions， which can effectively reduce the delivery cost and improve the distribution efficiency； the lower the minimum state of charge of vans and unmanned vehicles， the smaller the delivery cost，which is of great significance for the future development of higher-performance batteries.

Abstract:

The intermitted traffic flow modeling needs to take many impact factors into consideration and usually suffer large randomness in traffic simulation analysis. In response， this paper presents a traffic flow model with generalized obstacle form which includes transverse traffic blocking and its interference into modeling. By extending the IDM car-following model to obstacle avoidance cases （IDM+） and simultaneously introducing a vehicle pre-decision control workflow （Pre-IDM+）， an intermitted traffic flow simulation platform under totally random traffic loading is built. Based on the platform， the random convergence and simulation updated time step sensitivity of traffic indexes on driving trajectory， traffic flow characteristics and vehicle control state are discussed quantitively in a single-lane pedestrian crossing scenario. The results show that the simulation accuracy and analysis efficiency can be balanced （average error<2%） by setting 200 of simulation sample size， and the change of simulation updated time step has significant impact on parking times and obstacle avoidance （maximum error up to 43%）. From the perspective of index reliability， the average speed， the average deceleration， the frequency of driving state switching， and the time proportion of free/following driving state perform a good evaluation consistency （random error and simulation updated time step impact both<1%）.

Abstract:

In this paper， we use data from traffic accident investigation reports to construct a traffic accident causation knowledge graph and analyze risk factors. Firstly， we construct the recognition model of named entities of traffic accident causation applicable to low data volume based on the fine-tuned UIE pre-training model for the generation of the entity set. Secondly， through the structured processing and ontology construction， the graph database Neo4j is used to store the traffic accident causation knowledge graph for visualization. Thirdly， based on the expert experience and pre-trained language text classification model， the traffic accident causation entities are standardized. Finally， a risk factor analysis method based on the traffic accident causation graph is constructed to mine triggering characteristics and contributions of each factor by analyzing the type distribution and degree distribution of standardized entities， and to perform the association rule mining. The results of these methods and analyses provide an in-depth understanding and exploration of historical accident risk factors.

Abstract:

In view of the co-exitance of rolling contact fatigue （RCF） crack initiation and wear growth in the curved switch rail of high-speed railway turnout， a prediction method of RCF crack initiation considering the wear in the curved switch rail was proposed. Taking the wheel loading position transfer and wheel-rail contact status when passing turnout along reverse and side direction as an example， and considering the profiles relationship between curved switch and stock rails， the wear and fatigue accumulation process of the curved switch rail was recreated. The development characteristics of wear and fatigue damage in the curved switch rail， changes in the wheel loading position transfer， and wheel-rail contact conditions were analyzed for predicting the initiation life and location of cracks in the curved switch rail. The results indicate that the traffic gross tonnage at each wear growth phase shows a fluctuation trend， which means that the wear grows with an irregularity process， during the process of crack initiation considering train passing with reverse and side direction. Moreover， a contrasting trend was observed in the wear growth rate between stock and curved switch rails. The RCF crack initiation life for a section with a top width of 35 mm of the curved switch rail is estimated to be approximately 11.7 MGT （million gross tonnage）. The crack initiation position is located at an area on the top of the rail about 10-15 mm away from its center and 1-3 mm below its surface.

Abstract:

Based on the alignment correction engineering for ballastless track on high-speed railways， a finite element model for the alignment correction of the CRTSⅡ slab ballastless track on the subgrade was established. A typical pushing scheme for alignment correction was selected， and the effects of different pushing pressures were simulated. The mechanical and damage performance of the ballastless track were analyzed. The effect of expanding the delamination zone and removing the wide and narrow joints was studied， and optimization suggestions for the alignment correction were proposed. The results show that the fake-crack of track-slabs is a critical mechanical control index， and the critical pushing pressure to ensure the components from crack is 0.58 MPa， corresponding to an alignment displacement of 1.50 mm. The interface between the track-slab and the wide and narrow joint is a critical control area for damage， and the critical pushing pressure to ensure interlayer from damage is 0.51 MPa， corresponding to an alignment displacement of 1.23 mm. To increase the alignment displacement， it is recommended to expand the delamination zone of the existing scheme by 3/4 of the track-slab length on each end. At the same time， the wide and narrow joints could be removed before alignment correction.

Abstract:

The microbial-induced calcite precipitation （MICP） method represents an ecologically friendly and sustainable microbial treatment and remediation technology designed for soil solidification and contamination， and the efficacy of the method depends on the microorganism adept at urease production. A comprehensive investigation was conducted to study the impacts of factors such as oscillating speed， temperature， medium pH on the growth and urease activity of Sporosarcina pasteurii. The underlying mechanisms of biomineralization precipitation were revealed by synergistically utilizing techniques such as Fourier transformation infrared spectroscopy， X-ray photoelectron spectroscopy， X-ray diffraction，and scanning electron microscopy. The findings unequivocally demonstrate that an oscillating speed of 210 r·min^-1 coincides with heightened levels of dissolved oxygen within the medium， thereby fostering elevated bacterial concentrations and augmented urease activity. The judicious utilization of an initial inoculum quantity amounting to 0.5% of the medium constituents engenders maximal nutrient consumption and precipitates rapid bacterial proliferation. A temperature of 30 ℃ is established as the ideal for fostering bacterial growth， striking a balance between avoiding dormancy due to lower temperatures and evading protein denaturation and inactivation attributed to excessive heat. The bacterial consortia exhibit a notable resilience across a pH spectrum spanning 5 to 10， with acidic conditions eliciting a prolonged interval for urease activity to attain its zenith. Despite this delay， the pinnacle of urease activity remains relatively unaltered， whereas an alkaline milieu is conducive to accentuating urease activity. Urea， as a pivotal determinant， exerts a direct influence on the adenosine triphosphate （ATP） synthesis， which is crucial for bacterial energy metabolism， and thus profoundly affecting both bacterial proliferation and urease activity. Notably， a urea concentration ranging from 5 to 25 g·L^-1 fosters expedited bacterial growth rates coupled with heightened urease activity. The MICP process was carried out on extracellular polymers of bacteria， and the generated calcium carbonate was mainly composed of rhombic calcite and a small amount of spherical vaterite.

Abstract:

In order to enhance the antibacterial properties of natural pyrethrins， a type of natural pyrethrin microcapsules was prepared using soy protein isolate（SPI） and salicylic acid（SA） as wall materials by complex coagulation method. Single-factor and orthogonal experiments were employed to optimize preparation conditions of pyrethrin microcapsules based on embedding rate and drug loading. The morphology， structure， thermal stability， slow-release capability， storage stability and antibacterial activity were characterized. The results indicate that the optimal conditions are pH 4.25， wall material concentration 2.0%， core-wall ratio 0.5， and SPI/SA mass ratio 2∶1. Under these conditions， the microcapsule exhibits an encapsulation efficiency of approximately 30.6%， a maximum drug loading capacity of 3.51%， and an average particle size of 38.3 μm. The microcapsule is spherical and complete， with a crack-free surface. FT-IR analysis confirms the successful embedding of pyrethroid components. Furthermore， the microcapsule demonstrates good thermal stability and sustained release performance at temperatures below 200 ℃. The effective antibacterial properties of salicylic acid against Escherichia coli and Staphylococcus aureus are retained but no antibacterial activity against Candida albicans. The storage stability of microcapsules under low-temperature and dark conditions is moderate， and a recommended shelf life of 3 months is suggested.

Abstract:

Based on the special structure of seal vibrissa with its ability to effectively inhibit vortex-induced vibrations， the behaviour of flow and aerodynamic noise around a seal-vibrissa-shaped cylinder was numerically simulated. Aerodynamic noise was measured in an anechoic wind tunnel， and the seal-vibrissa-shaped cylinder case was compared with the cases of cylindrical and elliptical bars in same characteristic dimensions. Results show that the alternative arrangement of the saddle and nodal planes of the seal-vibrissa-shaped cylinder leads to three-dimensional flow separations and suppresses the shear layer interactions， which improves the flow stability with no dominant coherent structures developed in the wake and thus suppresses the lift fluctuations on solid wall surfaces. The morphology of the seal-vibrissa-shaped cylinder inhibits the regular vortex shedding of Karman vortex street which occurs in a cylinder wake， and consequently eliminates the tonal peak of flow-induced noises. Thereby， the sound pressure level is reduced at main frequencies. The experimental results verify the accuracy of numerical simulations.

Abstract:

The rotor of a 12/12 bearingless switched reluctance motor （BSRM） has a salient pole structure， and the stator-rotor flux changes with the rotor position， causing the suspension force to vary with the rotor position， exhibiting time-varying characteristics.To address the time-varying suspension system control problem， firstly， the suspension force characteristics of 12/12 BSRM were analyzed by finite element analysis， which clarifies the dynamic variation law between the suspension flux hinge and rotor position. Secondly， the Maxwell stress method with the advantage of regional modeling was used to analyze the magnetic flux and a mathematical model of the suspension force considering the edge flux was constructed. Based on the time-varying suspension force model， a nominal constant feedback model and a time-varying suspension force component compensator were constructed， and the time-varying suspension force control system was converted to a constant suspension force control system， which realizes the decoupling control of the suspension force on the rotor position. Finally， simulation and experimental studies were conducted on the accuracy of the time-varying suspension force mathematical model， the performance of the time-varying suspension force component compensator， and the performance of the control system， verifying the effectiveness and progressiveness of the proposed control strategy.