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.

A study of the load transfer behavior of fully grouted rock bolts with analytical modelling

Fully grouted rock bolts have been used in mining industry for many years.Much research has been conducted to evaluate the load transfer behavior of fully grouted rock bolts with experimental programs.However,compared with that,less work has been conducted with analytical modelling.Therefore,in this paper,the authors used an analytical model to study the load transfer behavior of fully grouted rock bolts.To confirm the credibility of this analytical model,an in-situ pull-out test was used to validate this model.There was a close match between the experimental result and the analytical result.Following it,a parametric study was conducted with this analytical model.The influence of coefficients,Young’s modulus of the rock bolt and the diameter of the rock bolt on the load transfer performance of rock bolts was studied.Furthermore,the load distribution along the fully grouted rock bolt was analytically studied.The results show that the axial load in the rock bolt decayed from the loaded end to the free end independent of the pull-out load.However,the trend of the load distribution curve was influenced by the pull-out load.This paper was beneficial for better understanding the load transfer mechanism of fully grouted rock bolts.

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.

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.

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.

Bearing capacity and load transfer mechanism of a static drill rooted nodular pile in soft soil areas

The static drill rooted nodular pile is a new type of pile foundation consisting of precast nodular pile and the surrounding cemented soil.This composite pile has a relatively high bearing capacity and the mud pollution will be largely reduced during the construction process by using this type of pile.In order to investigate the bearing capacity and load transfer mechanism of this pile,a group of experiments were conducted to provide a comparison between this new pile and the bored pile.The axial force of a precast nodular pile was also measured by the strain gauges installed on the pile to analyze the distribution of the axial force of the nodular pile and the skin friction supported by the surrounding soil,then 3D models were built by using the ABAQUS finite element program to investigate the load transfer mechanism of this composite pile in detail.By combining the results of field tests and the finite element method,the outcome showed that the bearing capacity of a static drill rooted nodular pile is higher than the bored pile,and that this composite pile will form a double stress dispersion system which will not only confirm the strength of the pile,but also make the skin friction to be fully mobilized.The settlement of this composite pile is mainly controlled by the precast nodular pile;meanwhile,the nodular pile and the surrounding cemented soil can be considered as deformation compatibility during the loading process.The nodes on the nodular pile play an important role during the load transfer process,the shear strength of the interface between the cemented soil and the soil of the static drill rooted pile is larger than that of the bored pile.

多道撑式深基坑垮塌事故连续破坏机理研究

随着城市地铁建设不断发展,多道撑式深基坑应用日益广泛,然而目前对于内撑式深基坑局部破坏引发连续破坏在空间上的传递规律仍缺乏系统研究。文章依托新加坡地铁Nicoll Highway基坑事故,建立三维有限差分模型,提出内支撑荷载传递百分比S1,i和荷载增量承担百分比S2,i两种支撑荷载(轴力)传递评价指标。对比分析了单位厚度平面应变模型与三维模型的模拟结果,探究了不同初始破坏支撑数量在不同位置发生初始破坏所引发的荷载重分布规律,同时还研究了围护结构体系刚度和强度对于连续破坏发展的影响。结果表明,三维模型可以避免平面应变模型传力路径单一的局限性,更好地反映出连续破坏在三维空间中的传递现象;初始破坏支撑所释放的荷载主要作用在紧邻层支撑;当失效荷载存在向下的传递路径时,紧邻初始破坏的上层和同层支撑承担的荷载增量明显减少;底层支撑的安全系数提高会减缓连续破坏在水平方向的发展;支撑刚度越大,在初始破坏后所承担的荷载增量越多;当墙体间无有效连接时,支撑连续破坏沿竖直方向发展的趋势更加显著。

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

基于扰动状态概念的砂土-混凝土桩接触面荷载传递模型研究

基于扰动状态概念理论,考虑砂土密实度对扰动函数的影响,建立混凝土桩-砂土接触面荷载传递模型。用混凝土板表征桩侧粗糙度效应,采用大型直剪仪开展不同密实度的砂土-混凝土桩接触面力学行为的试验模拟,研究砂土密实度对混凝土桩-砂土接触面的力学特性的影响规律,分析接触面模型初始剪切系数、模型扰动参数(A和Z)对桩-砂土接触面荷载传递模型的作用机制。研究结果表明:1)混凝土桩-砂土接触面易呈现应变软化,在低法向应力条件下,混凝土桩-密砂接触面的应变软化程度最大。2)模型扰动参数Z在数值上近似等于孔隙比。模型扰动参数A越大,砂土与混凝土桩接触面的软化显著程度越大。参数A随着密实度增大而增大。随着法向应力增大,密砂的扰动参数A呈近似线性衰减,松砂和中密砂的扰动参数A近似呈双折线衰减。3)初始剪切系数k_s随着法向应力增大而增大,密实度越大,增速越快。4)基于扰动状态概念的桩-砂土接触面荷载传递模型可靠、参数的物理意义明确且易确定,能很好地表征桩-砂土接触面的应变软化及硬化等力学特征。

基于扰动理论修正的桩-土接触面荷载传递模型及其应用

利用硬化模型、双曲线模型、指数模型以及软化模型模拟的桩-土接触关系存在参数取值困难、误差大的问题。为深入研究土-结构接触面的强度与变形机理,基于扰动理论,假定完整状态接触单元的抗剪强度服从线弹性模型,而扰动部位则服从塑性模型,建立修正的桩-土接触面荷载传递模型。该模型参数分析表明,参数k、η对模型τ-s曲线形态影响大,而参数τf、ζ对模型τ-s曲线形态影响很小;并通过大型桩-土接触面室内直剪试验,量化接触面上剪切应力与剪切位移的关联性,进一步确定修正桩-土接触模型内部计算参数。结果表明模型τ-s曲线与试验曲线吻合较好,验证了模型的合理性。扰动桩-土接触模型既能描述桩侧应变软化也能描述硬化特性,有助于理解复杂应力条件下桩-土接触面的强度计算与变形机理。

基于GRU门控单元网络的电力负荷预测研究

准确预测电力负荷,有利于提高电力系统供需平衡,为提高电力负荷预测精度,提出一种基于迁移学习的电力负荷预测模型。该模型以门控循环单元模型(GRU)为基础模型,通过设定最大均值差异算法阈值,从而选择迁移学习的模型,最终实现电力负荷雨预测。仿真结果表明,所提模型可准确预测电力负荷数据,相较于BPNN模型和LSTM模型,所提出模型的MAPE值更低,为17.5%,分别降低了15%和7.5%,具有更高的预测准确度,可用于电力负荷预测实际应用中。

The Effects of Fatigue Cracks on Fastener Loads during Cyclic Loading and on the Stresses Used for Crack Growth Analysis in Classical Linear Elastic Fracture Mechanics Approaches

High strength threaded fasteners are widely used in the aircraft industry, and service experience shows that for structures where shear loading of the joints is significant, like skin splices, fuselage joints or spar caps-web attachments, more cracks are initiated and grow from the edges of the fastener holes than from features like fillets radii and corners or from large access holes. The main causes of this cracking are the stress concentrations introduced by the fastener holes and by the threaded fasteners themselves, with the most common damage site being at the edge of the fastener holes. Intuitively, it is easy to visualize that after the crack initiation, during the growth stages, some of the load transferred initially by the fastener at the cracked hole will decrease, and it will be shed to the adjacent fasteners that will carry higher loads than in uncracked condition. Using currently available computer software, the method presented in this paper provides a relatively quick and quantitatively defined solution to account for the effects of crack length on the fastener loads transfer, and on the far field and bypass loads at each fastener adjacent to the crack. At each location, these variations are determined from the 3-dimensional distribution of stresses in the joint, and accounting for secondary bending effects and fastener tilt. Two cases of a typical skins lap splice with eight fasteners in a two rows configuration loaded in tension are presented and discussed, one representative for wing or fuselage skins configurations, and the second case representative for cost effective laboratory testing. Each case presents five cracking scenarios, with the cracks growing from approx. 0.03 inch to either the free edge, next hole or both simultaneously.

并联负荷分配控制系统设计研究

多个储能装置并联时,如何提高储能装置剩余容量的利用率,完成每个储能装置能量按需分配,并保证系统平稳安全运行的问题受到研究人员的关注。对多个储能装置并联系统的能量管理策略进行研究,基于输出电流和储能装置的剩余容量引出负荷系数的概念,并提出了中间负荷系数控制模式,同时基于此控制模式进行了建模和三环控制系统传递函数的推导。通过3个储能装置并联系统进行仿真和实验,验证了所提负荷分配控制策略的稳定性与合理性,避免了储能装置因过度放电或过度充电提前退出运行,并达到了按照剩余容量进行负荷分配的目标。

基于CNN-LSTM的重型自卸车侧翻预警模型

为解决重型自卸车的侧翻预警问题,基于CNN-LSTM神经网络构造了重型自卸车的侧翻预警模型。利用Trucksim与MATLAB/Simulink搭建了重型自卸车仿真模型,以横向载荷转移率等于±0.85为侧翻阈值,提取了不同工况下的车辆运行参数,利用车辆运行参数,训练CNN-LSTM重型自卸车侧翻预警模型,并分别与基于CNN、LSTM搭建的预警模型对比。结果表明:CNN-LSTM重型自卸车侧翻预警模型预测准确率为98.31%;感受性曲线的曲线下面积为0.999,高于由单一神经网络所搭建的侧翻预警模型。

Behaviour of Earth Dam under Seismic Load Considering Nonlinearity of the Soil

The stability and safety are very important issues for the dam structure which are built in seismic regions. The dam body consists of soil materials that behave nonlinearly modelled with finite elements. The numerical investigation employs a fully nonlinear finite element analysis considering linear and elastic-plastic constitutive model to describe the material properties of the soil. In this paper, seismic analysis of an earthen dam is carried out using Geo-Studio software based on finite element method. Initially, the in-situ stress state analysis has been done before the earthquake established, and then its results are used in the seismic analysis as a parent analysis. A complete parametric study is carried out to identify the effects of input motion characteristics, soil behaviour and strength of the shell and core materials on the dynamic response of earthen dams. The real earthquake record is used as input motions. The analysis gives the overall pattern of the dam behaviour in terms of contours of displacements and stresses.

溶洞型基桩承载特性离心试验及承载力计算方法

为确定溶洞对基桩荷载传递规律和承载特性的影响,通过离心模型试验,研究了4种洞高、4种洞跨和3种溶洞层数下基桩的荷载-沉降规律、竖向承载力、荷载分担比、轴力和侧阻的变化;引入敏感分析模型,研究了基桩竖向承载力对两因素的敏感性;采用荷载传递法建立了穿过溶洞的基桩荷载-沉降计算公式。结果表明:洞高、洞跨、层数的增加会削减基桩竖向承载力,洞高对承载力的影响大于洞跨;两因素变化下溶洞处桩身轴力几乎不衰减,单位侧阻骤减至接近零;采用改进的荷载传递法和双曲线模型建立了基桩承载力计算公式,计算结果与试验结果相比,最大误差5.96%,具有较高吻合度。研究成果可为岩溶区基桩竖向承载力和沉降计算提供参考。

可回收自平衡法检测装置研发及力学特性分析

针对传统桩基静载试验中存在的主要问题,研发了一种可回收自平衡法桩基承载力检测装置,建立了新型可回收检测结构作用下的试桩荷载传递模型,推导出层状地基中桩身的荷载传递矩阵,并通过实际工程三维有限元计算结果,验证了理论解析方法的可靠性。结合现场实测获取的荷载-位移、桩身轴力等数据,探究了该结构的工作机理。结果表明:①该新型结构装配化程度高,测试周期短,能耗低,试验空间要求小,具备推广价值。②理论解析模型得出的桩身轴力、荷载位移曲线与实测结果吻合较好,均在误差允许范围内。③相对于传统荷载箱测试结构,该新型结构测得承载力精度提高3.5%。因此,该理论模型与新型结构在实际工程中具备很大的适用性与推广价值。

汽车爆胎的载荷转移建模及仿真分析

汽车发生爆胎后容易造成交通事故,特别是在高速行驶的情况下,由爆胎引起的交通事故占比32%,其中死亡事故更是高达49%[1]。当高速行驶的汽车发生爆胎后,行驶路线会发生改变,并且汽车会处于横摆与侧翻的失控状态,所以对爆胎汽车的行驶状态进行研究是非常必要的。首先,通过研究汽车爆胎发生后,爆胎车轮的滚动半径变化,爆胎汽车姿态发生变化从而会使汽车转向系统的转向角及车轮侧偏角发生改变;其次,通过研究汽车爆胎发生后,汽车的重心将发生转移从而引起四个车轮上的垂直载荷发生转移,从而导致各个车轮上的侧偏力大小发生改变;最后,通过分析汽车爆胎过程中各个车轮侧偏角的改变以及垂向载荷的转移引起各个车轮上的侧偏力的改变,联合建立爆胎汽车二自由度操纵动力学模型。并利用Matlab/Simulink搭建仿真模型,得出汽车侧向加速度、横摆角速度的变化曲线。仿真结果表明,在车速为120km/h时,汽车发生爆胎的运动过程中,考虑垂向载荷转移的情况相比于没有考虑垂向载荷转移的情况更能准确描述爆胎汽车方向失稳的真实运动过程。

制取大型块状冰的制冷系统设计

目前制取大型块状冰的制冷系统尚不成熟.对制取大型块状冰蒸发器的传热特点进行了设计及分析,建立了大型块状冰蒸发器的传热模型,得到了求解冻结成固定厚度块状冰所需时间的计算方法,以及结冰时间随厚度变化的预测公式.结合工业标准设备对制冰系统其他设备(压缩机、冷凝器、热力膨胀阀等),进行了选型设计计算.所建蒸发器传热模型对制取块状冰的制冷系统优化设计有指导意义.

基于双界面滑移耦合的水泥土锚杆荷载传递模型

水泥土锚杆的承载过程伴随筋体—黏结体界面和黏结体—岩土体界面的黏结强度调动,界面剪应力的径向传播机制受到不同界面附近材料的应力和变形条件影响,对水泥土锚杆进行荷载传递分析需考虑双界面的剪切变形耦合。结合锚杆受力变形分析常用的荷载传递法和剪切位移法,将二者分别用于界面剪应力在锚杆轴向和径向引起的变形分析计算,考虑锚杆双界面的剪应力与剪切变形耦合,建立基于界面特性测试的水泥土锚杆双界面滑移耦合荷载传递分析模型。通过水泥土的材料性质试验及单元体尺度和模型试验尺度的水泥土锚杆拉拔试验,获得了模型的计算参数取值,并验证了模型对锚杆拉拔响应的预测能力。