Performance of composite foundations with different load transfer platforms and substratum stiffness over silty clay

The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations.It is crucial to understand the stress distribution across the embankment width and the behaviour of unreinforced foundations.Thus,five centrifuge tests were conducted to examine the bearing and deformation behaviours of NPRS(Non-Connected Piled Raft Systems)and GRPS(GeosyntheticReinforced Pile-Supported systems)with varying substratum stiffness,then a comparative analysis was conducted on embankment settlement,pressures underneath the embankments,and axial forces along the piles.The results indicated that greater substratum stiffness correlates with reduced settlement and deformation at various depths.Deformation occurring 5 meters from the embankment toe includes settlement in NPRS and upward movement in GRPS.The potential sliding surface is primarily located within the embankment in NPRS,whereas it may extend through both the embankment and foundation in GRPS.The pile-soil stress ratio and efficiency in NPRS are higher than in GRPS across the embankment.The axial force borne by end-bearing piles is significantly greater than that by floating piles.As the buried depth increases,the axial force in GRPS initially rises then declines,whereas in NPRS,it remains relatively constant within a certain range before decreasing.This study aids in assessing the applicability of composite foundations in complex railway environments and provides a reference for procedural measures under similar conditions.

Numerical and theoretical study of load transfer behavior during cascading pillar failure

To further study the load transfer mechanism of roofemulti-pillarefloor system during cascading pillar failure(CPF),numerical simulation and theoretical analysis were carried out to study the three CPF modes according to the previous experimental study on treble-pillar specimens,e.g.successive failure mode(SFM),domino failure mode(DFM)and compound failure mode(CFM).Based on the finite element code rock failure process analysis(RFPA^(2D)),numerical models of treble-pillar specimen with different mechanical properties were established to reproduce and verify the experimental results of the three CPF modes.Numerical results show that the elastic rebound of roofefloor system induced by pillar instability causes dynamic disturbance to adjacent pillars,resulting in sudden load increases and sudden jump displacement of adjacent pillars.The phenomena of load transfer in the roofemulti-pillarefloor system,as well as the induced accelerated damage behavior in adjacent pillars,were discovered and studied.In addition,based on the catastrophe theory and the proposed mechanical model of treble-pillar specimen edisc spring group system,a potential function that characterizes the evolution characteristics of roof emulti-pillarefloor system was established.The analytical expressions of sudden jump and energy release of treble-pillar specimenedisc spring group system of the three CPF modes were derived according to the potential function.The numerical and theoretical results show good agreement with the experimental results.This study further reveals the physical essence of load transfer during CPF of roof emulti-pillarefloor system,which provides references for mine design,construction and disaster prevention.

Intelligent Power Grid Load Transferring Based on Safe Action-Correction Reinforcement Learning

When a line failure occurs in a power grid, a load transfer is implemented to reconfigure the network by changingthe states of tie-switches and load demands. Computation speed is one of the major performance indicators inpower grid load transfer, as a fast load transfer model can greatly reduce the economic loss of post-fault powergrids. In this study, a reinforcement learning method is developed based on a deep deterministic policy gradient.The tedious training process of the reinforcement learning model can be conducted offline, so the model showssatisfactory performance in real-time operation, indicating that it is suitable for fast load transfer. Consideringthat the reinforcement learning model performs poorly in satisfying safety constraints, a safe action-correctionframework is proposed to modify the learning model. In the framework, the action of load shedding is correctedaccording to sensitivity analysis results under a small discrete increment so as to match the constraints of line flowlimits. The results of case studies indicate that the proposed method is practical for fast and safe power grid loadtransfer.

Optimal allocation method of electric/air braking force of high-speed train considering axle load transfer

Reasonable distribution of braking force is a factor for a smooth,safe,and comfortable braking of trains.A dynamic optimal allocation strategy of electric-air braking force is proposed in this paper to solve the problem of the lack of consideration of adhesion difference of train wheelsets in the existing high-speed train electric-air braking force optimal allocation strategies.In this method,the braking strategy gives priority to the use of electric braking force.The force model of a single train in the braking process is analyzed to calculate the change of adhesion between the wheel and rail of each wheelset after axle load transfer,and then the adhesion of the train is estimated in real time.Next,with the goal of maximizing the total adhesion utilization ratio of trailer/motor vehicles,a linear programming distribution function is constructed.The proportional coefficient of adhesion utilization ratio of each train and the application upper limit of braking force in the function is updated according to the change time point of wheelset adhesion.Finally,the braking force is dynamically allocated.The simulation results of Matlab/Simulink show that the proposed algorithm not only uses the different adhesion limits of each trailer to reduce the total amount of braking force undertaken by the motor vehicle,but also considers the adhesion difference of each wheelset.The strategy can effectively reduce the risk and time of motor vehicles during the braking process and improve the stability of the train braking.

A hardening load transfer function for rock bolts and its calibration using distributed fiber optic sensing

Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.

Quantification of the Vertical Load Applied to the Pavement during Cornering Maneuver of a Battery Electric Commercial Vehicle

The wheel loads of heavy trucks are the major source of pavement damage,given the repeated loadings imposed by them due to transient events and surface irregularities.While related studies focus on steady-state context regarding simplified vehicle’s parameters and ideal pavement conditions,this paper aims to analyze the vertical load applied to the pavement by considering cornering maneuver as a transient event,on a battery electric vehicle truck.In this concern,measurements were performed on a rigid truck,with two steering front axles,in a closed course proving ground.The relationship has been presented between vehicle’s speed,lateral acceleration and transferred vertical load for a given curve radius of 85.6 m and 3.7°of transversal slope.The measurements results indicated that for every 10 km/h increasing on the vehicle’s speed,additional 110 kgf will be transferred to the pavement on the outer side of the cornering radius.This value itself could not be considered high,but it will be also added to the static load,or overload in some truck applications.

A priority-based dynamic load transfer algorithm for cellular/WLAN integrated networks

For the integration network of a cellular network and a wireless local area network （WLAN）, a priority-based dynamic load transfer （PDLT） algorithm is proposed. The dynamic vertical handoffs by call admission control are jointly determined by the network conditions and the traffic characteristics in combination with the location-condition of mobile terminals. When there is no bandwidth resource available in the cellular network or WLAN, the proposed PDLT algorithm allows an incoming voice call or data call within the overlapping area of the cellular network and the WLAN to be directed to the spare network; meanwhile, by dynamically computing the occupancy of the bandwidth resource, the proposed PDLT algorithm also allows an ongoing voice call or data communication to be transferred to the network with a sufficient bandwidth resource according to the given threshold to balance the number of voice/data calls in the two networks. The analysis results of a two-dimensional Markov model and the simulation results show that the PDLT algorithm can effectively enhance the whole integrated network＇ s traffic, reduce the blocking probability of new calls and increase the data throughput, and thus decrease the response time for various services.

Optimization of the fully grouted rock bolts for load transfer enhancement

The purpose of this study is to investigate the role of bolt profile configuration in load transfer capacity between the bolt and grout.Therefore,five types of rock bolts are used with different profiles.The rock bolts are modeled by ANSYS software.Models show that profile rock bolt T_3 and T_ with load capacity 180 and 195 kN in the jointed rocks,are the optimum profiles.Finally,the performances of the selected profiles are examined in Tabas Coal Mine by FLAC software.There is good subscription between the results of numerical modeling and instrumentation reading such as tells tale,sonic extensometer and strain gauge rock bolt.According to the finding of this study,the proposed pattern of rock bolts,on 7 + 6 patterns per meter with 2 flexi bolt(4 m) for support gate road.

Analytical method of load-transfer of single pile under expansive soil swelling

The elastic differential equations of load-transfer of single pile either with applied loads on pile-top or only under the soil swelling were established,respectively,based on the theory of pile-soil interaction and the shear-deformation method.The derivation of analytic solution to load-transfer for single pile in expansive soil could hereby be obtained by means of superposition principle under expansive soils swelling.The comparison of two engineering examples was made to prove the credibility of the suggested method.The analyzed results show that this analytic solution can achieve high precision with few parameters required,indicating its' simplicity and practicability in engineering application.The employed method can contribute to determining the greatest tension along pile shaft resulting from expansive soils swelling and provide reliable bases for engineering design.The method can be employed to obtain various distributive curves of axial force,settlements and skin friction along the pile shaft with the changes of active depth,vertical movements of the surface and loads of pile-top.

Vertical bearing capacity of pile based on load transfer model

The load transfer analytical method is applied to study the bearing mechanism of piles with vertical load in this paper. According to the different hardening rules of soil or rock around the pile shaft, such as work-softening, ideal elasto-plastic and work-hardening, a universal tri-linear load transfer model is suggested for the development of side and tip resistance by various types of soil (rock) with the consideration of sediment at the bottom of the pile. Based on the model, a formula is derived for the relationship between the settlement and load on the pile top to determine the vertical bearing capacity, taking into account such factors as the characteristics of the stratum, the side resistance along the shaft, and tip resistance under the pile tip. A close agreement of the calculated results with the measured data from a field test pile lends confidence to the future application of the present approach in engineering practice.

Uplift behavior and load transfer mechanism of prestressed high-strength concrete piles

Prestressed high-strength-concrete (PHC) tube-shaped pile is one of the recently used foundations for soft soil. The research on uplift resistance of PHC pile is helpful to the design of pile foundations. A field-scale test program was conducted to study the uplift behavior and load transfer mechanism of PHC piles in soft soil. The pullout load tests were divided into two groups with different diameters, and there were three piles in each group. A detailed discussion of the axial load transfer and pile skin resistance distribution was also included. It is found from the tests that the uplift capacity increases with increasing the diameter of pile. When the diameter of piles increases from 500 to 600 mm, the uplift load is increased by 51.2%. According to the load-displacement (Q-S) curves, all the piles do not reach the ultimate state at the maximum load. The experimental results show that the piles still have uplift bearing capacity.

Load Transfer Test of Post-Tensioned Anchorage Zone in Ultra High Performance Concrete

Researches on ultra-high performance concrete (UHPC) have been conducted worldwide owing to its outstanding durability and strength performances. The exploitation of the mechanical properties of UHPC will render it possible to achieve economic design through substantial reduction in the cross sectional dimensions and simplification in the reinforcement arrangement. This paper investigates experimentally the load transfer in the prestressed concrete anchorage zone. To provide distinctive features of UHPC compared to ordinary concrete, the cross sectional dimensions of the member were reduced and the stress distribution, deformation and cracking pattern of the PS anchorage zone were examined experimentally according to the degree of reinforcement of the members chosen. The distributions of the bursting stress, spalling stress and longitudinal edge stress in the specimens were observed according to the various types of reinforcement. All the specimens satisfied the load-bearing capacity criterion specified by the European ETAG-013 guidelines and their stress distributions were similar to those in the PS anchorages of post-tensioned members applying ordinary concrete. The cracks propagated longitudinally with lengths up to twice the cross sectional dimensions and their width was smaller than when applying ordinary concrete owing to the bridging effect of the steel fibers in UHPC. Accordingly, the exploitation of the high strength of UHPC enabled us to secure the resistance of the anchorage with no need for particular reinforcing devices.

Simulation and Experimental Design of Load Adaptive Braking System on Two Wheeler

The braking quality is considered the main execution of the adaptive control framework that impacts the vehicle safety and rides solace astoundingly notably the stopping distance.This research work aims to create a pattern and design of an electromechanically adjusted lever that multiplies the applied braking force depending on the inputs given by the sensors to reduce the stopping distance of the vehicle.It is carried out using two main parts of the two-wheeler vehicle:thefirst part deals with the detection of load acting on the vehicle and identifying the required braking force to be applied,and the second part deals with the micro-controller which activates the stepper motor for varying the mechanical leverage ratio from various loads on the vehicle using two actively movable wedges.The electromechanically operated variable braking force system is developed to actuate the braking system based on the load on the motorcycle.The MATLAB simulation and experimental work are carried out for various loading(driver and pillion)conditions on a two-wheeler.The results indicate that the proposed electronically operated braking system is more effective than the conventional braking system for various loads and vehicle speeds.Specifically,the stopping distance of the vehicle is decreased significantly by about 4.9%between the con-ventional braking system and the simulated proposed system.Further,the experi-mental results show that the stopping distance is condensed by about 4.1%.The validation between simulated and experimental results revealed a great deal with the least error percentage of about 0.8%.

高速铁路无砟轨道车辆荷载传递特性研究

为进一步探讨无砟轨道荷载设计参数取值,为我国时速400 km及以上高速铁路建设提供重要理论支撑,通过开展无砟轨道静力分析以及钢轨焊缝、车轮扁疤激励下车辆-轨道动力相互作用,揭示列车静、动力载荷特征及传递规律;同时根据轨道承载特点和无砟轨道设计原理,提出车辆竖向设计荷载取值建议。研究结果表明:(1)高速列车车轮扁疤和钢轨焊缝不平顺将造成显著的轮轨冲击,其轮载动载系数最大可达5.79,远高于现行规范取值;扣件系统对扁疤和焊缝不平顺引起的轮轨力高频成分衰减作用明显,扣件支反力的动载系数最大为2.64;(2)钢轨焊缝不平顺引起的轮轨冲击力随着车速提高以及焊缝不平顺幅值的增大而迅速增大,建议500 km/h及以下高速铁路的钢轨焊缝平直度标准取0.2 mm/m;(3)列车轮载通过扣件支反力作用于轨道板,从传递特性的角度来说,以扣件支反力作为轨道板竖向设计荷载更为合理,其动载系数可取3.0,且能满足400 km/h及以上高速铁路的行车需求。

集中式馈线自动化配电网供电可靠性评估

计及集中式馈线自动化的配电网可靠性评估尚存在较多研究空白,且多数研究仅计及故障停电的影响,在考虑预安排检修容量约束的情况下,计及负荷转供影响,结合馈线自动化的类型及运行逻辑,依据馈线自动化相关技术指标,对恢复供电过程中出现的负荷点进行详细分类,推导出不同类型负荷期望恢复供电时间和配电网供电可靠性指标计算公式。结合算例进行分析可知,不同终端配置下馈线系统平均停电持续时间SAIDI可减少0.95~1.08 h/(用户·a),说明了优化终端配置可有效提高配电网供电可靠性,证明了所提评估方法的准确性和实用性,并比较了不同终端配置对可靠性的影响。

考虑姿态稳定性的智能客车轨迹跟踪控制研究

针对智能客车行驶中遇到突发情况时驾驶员应急激烈操作以及车辆传感器识别误差导致车辆路径规划不合理引起的车辆侧翻,提出一种基于车身姿态稳定性的轨迹跟踪控制策略.根据现有主动防侧倾研究基础推导智能客车目标侧倾角算法,以横向载荷转移率为侧翻指标,采用卡尔曼滤波算法进行车辆参数估计,实现横向载荷转移率预测.根据智能客车横向载荷转移率预测值设计基于差动制动的纵向控制策略、考虑车身侧倾和俯仰运动的垂向控制策略以及轨迹跟踪横向控制策略,最后通过仿真验证上述策略控制效果.结果表明,基于车身姿态稳定性的轨迹跟踪控制策略在车辆行驶遇到突发情况驾驶员激烈操作时能够保证车辆行驶稳定,在智能客车轨迹跟踪过程中能降低车辆侧翻风险.

城市中压配电网雪花格式网架结构初探

为适应新型电力系统建设需求,提出一种适合国情的雪花格式网架结构。首先,总结国内外典型城市中压配电网结构的特征与优缺点;然后,结合天津已有网架结构,提出雪花格式网架结构及其构建方法;其次,分析测算雪花网结构的负荷转移能力、可靠性与效率效益水平;最后,从结构形式、适合场景等方面给出雪花网结构与花瓣结构等的综合对比情况。结果表明,雪花格式网架结构具有一定综合比较优势,可为中压配电网远景目标网架规划提供指导。

考虑纵径向热应变的竖向受荷能量桩简化分析方法

为探究温度对能量桩荷载传递机理及相关力学响应的影响,引入平面瞬态温度场方程,将温度场与应力场解耦。基于平面应力模型,将能量桩与桩周土考虑为具有协调变形的整体,计算了径向热应力。在此基础上,将其与双曲线荷载传递模型结合,对桩土界面处的极限摩阻力进行修正。将纵向热应变考虑在竖向荷载传递方程中,得到可同时衡量纵向和径向热效应的竖向受荷能量桩承载特性分析方法。利用增量法对能量桩荷载传递控制方程进行求解,得到桩身轴力、桩侧阻力、桩身位移等相关力学响应。通过与既有文献进行对比,验证了该模型的合理性。通过参数分析,研究了温度和竖向力作用下能量桩的荷载传递特性。结果表明:温度会改变能量桩的荷载传递特性,提高能量桩的运行温度可小幅增加其承载力。该文方法的计算流程清晰,可为能量桩的设计提供参考。

桩顶荷载及温度循环对黄土地基中能量桩承载性状影响研究

为对比分析未经过温度循环的普通桩与能量桩竖向承载变形性状,开展黄土地基中能量桩温度循环试验。模型桩为现浇钢筋混凝土灌注桩,黄土为人工配制重塑黄土。研究结果表明:温度循环弱化黄土地基中能量桩桩身侧阻、增强能量桩桩底端阻,温度循环过程中桩顶工作荷载越大,桩侧阻的弱化作用及桩端阻的增强作用越大,这导致能量桩的竖向抗压承载力比普通桩有明显的提高。另外,根据模型试验结果,通过数据拟合建立桩土界面摩阻力-桩土相对位移及桩端土反力-桩端沉降双曲线函数模型,并确定模型参数,其函数计算结果与试验结果对比表明本文模型能合理反映温度循环及桩顶工作荷载大小对桩基承载力的影响。研究结果可为黄土地区能量桩的安全设计提供一定参考。

某迫榴炮击针疲劳寿命仿真与提升研究

击针大多采用细长及变截面结构,在循环撞击力作用下,易引起结构应力集中及交变应力,经常出现疲劳断裂故障,严重影响自动武器的可靠性,甚至威胁到作战人员安全。某迫榴炮击针在试验中偶发断裂现象,疲劳寿命约200发左右,为了提升该击针疲劳寿命,基于载荷传递过程,建立了击针在火药气体反冲力下高速运动与限位块的瞬态撞击模型,获取击针撞击过程交变应力,通过循环载荷作用下击针疲劳寿命评估,计算击针疲劳寿命与试验现象基本一致,验证了计算模型的准确性。在此基础上,开展了不同材料击针疲劳寿命提升研究,研究表明,将击针材料由PCrNi3Mo更换为30CrNi2MoVE后,击针疲劳寿命由215发提升到1670发,提升效果显著,改进后的击针经实弹射击试验验证在规定寿命周期内未发生断裂现象。