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.

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.

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.

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.

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.

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.

Simulation of roof snow loads based on a multi-layer snowmelt model:Impact of building heat transfer

To investigate the impact of building heat transfer on roof snow loads,roof snow loads and snow load thermal coefficients from 61 Chinese sites over a period of 50 years are simulated based on basic meteorological data such as temperature,humidity,wind speed,and precipitation,and a multi-layer snowmelt model considering the building heat transfer.Firstly,the accuracy of the multi-layer snowmelt model is validated using the data of observed ground snow load and roof snow melting tests.The relationship between meteorological conditions,snow cover characteristics,and thermal coefficients of snow loads in three representative sites is then studied.Furthermore,the characteristics of thermal coefficients in each zone are analyzed by combining them with the statistical results of meteorological data from 1960 to 2010,and the equations of thermal coefficients in different zones on indoor temperatures and roof heat transfer coefficients are fitted separately.Finally,the equations in this paper are compared with the thermal coefficients in the main snow load codes.The results indicate that the snowmelt model using basic meteorological data can effectively provide samples of roof snow loads.In the cold zone where the snow cover lasts for a long time and does not melt easily,the thermal coefficients of the snow loads on the heating buildings are lower than those in the warm zone due to the long-term influence of the heat from inside the buildings.Thermal coefficients are negatively correlated with indoor temperatures and roof heat transfer coefficients.When the indoor temperature is too low or the roof insulation is good,the roof snow load may exceed the ground snow load.The thermal coefficients for heated buildings in the main snow load codes are more conservative than those calculated in this paper,and the thermal coefficients for buildings with lower indoor temperatures tend to be smaller.

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。

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。

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。

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。

螺栓连接结构冲击载荷传递特性及冲击响应行为研究进展综述

目的通过探讨复杂装备结构中螺栓连接结构在冲击载荷条件下的力学响应特征,以及这些特征如何影响装备结构的应力波传播、能量耗散和整体结构响应;同时,关注螺栓自身的变形和破坏对关键部件乃至整个系统稳定性和安全性的潜在影响,特别是在武器装备中可能引发的灾难性后果,旨在进一步优化螺栓连接结构的设计,提高其在极端载荷条件下的性能和可靠性。方法系统调研国内外文献,总结螺栓连接结构冲击载荷传递特性及冲击响应行为的研究进展,涉及的研究方法包括试验研究、有限元模拟和理论分析等。结论螺栓连接结构的冲击响应行为对装备整体的稳定性和安全性具有重要影响。通过对现有文献的分析,提出了未来研究的建议。

基于Rayleigh分布扰动状态概念的单桩承载特性研究

基于扰动状态概念(Disturbed State Concept,DSC),结合Rayleigh分布从微观角度描述桩-土界面荷载渐进性传递特性,建立了基于DSC理论的桩侧及桩端荷载传递模型,给出了模型参数确定方法,并验证了模型的合理性.同时结合桩侧及桩端荷载传递模型,提出了一种分析单桩承载特性的迭代算法并验证其合理性.通过算法计算得到的单桩承载特性与案例实测值有较好的一致性,且可较好地反映侧阻及端阻硬化、软化等特性.变参数分析结果表明,基于DSC理论的桩侧及桩端荷载传递模型对不同土层、不同桩基施工工艺都有好的适用性,可较准确地描述桩-土界面荷载传递特性.

穿越充填溶洞时单桩沉降计算方法研究

采用圆孔扩张理论提出竖向受荷桩周地层对充填溶洞的水平和竖向作用力计算方法,采用Mindlin解建立溶洞段应力增量计算方法,基于桩-土(岩)界面、桩-溶洞界面的Boxlucas1荷载传递模型提出考虑地层-溶洞-桩共同作用的穿越充填溶洞型单桩沉降迭代计算方法。通过案例分析验证本文计算方法的合理性。根据参数分析结果,研究溶洞与桩顶的距离、溶洞半径、溶洞充填物剪切强度、桩径、桩长等对单桩承载特性的影响规律。研究结果表明:本文建立的计算方法可用于分析单桩穿越单个或多个充填溶洞时的承载特性;充填溶洞距离桩端越远、半径越小、充填物剪切强度越强,单桩承载力越大。

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。

建筑内热源滞后冷负荷监测模型研究

准确获取内热源实时冷负荷对于制定供暖空调系统节能调控策略及降低建筑运行能耗具有重要意义,而辐射热传递过程产生的滞后冷负荷是内热源冷负荷计算的难点,为此,基于围护结构蓄放热规律、热传递特性及传递函数原理等建立内热源滞后冷负荷监测模型,该模型为10阶传递函数。为了简化计算过程、提高计算精度,利用辐射时间系数对该模型进行参数辨识及降阶分析,最终得到2阶传递函数。建立试验系统对模型进行验证,结果显示,模型的平均绝对百分比误差为8.19%。内热源滞后冷负荷监测模型可依托能耗监测平台实现负荷的在线监测,对描述滞后冷负荷的时间延迟规律及幅度衰减特性具有理论意义,为制定供暖空调系统节能调控策略提供理论依据。

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.

居住区建筑布局对建筑外表面对流换热系数及建筑用能负荷影响研究

建筑外表对流换热系数(CHTC)是影响建筑能耗模拟(BES)结果的重要参数。BES工具中既有的CHTC计算方法不适合建筑群能耗模拟,这将增大建筑能耗预测的不准确性。文章考虑了建筑布局对建筑外表面CHTC的影响,基于优化后的建筑能耗计算模型,研究寒冷地区居住区建筑布局对建筑用能负荷的影响。