Parametric analysis of thermal effect on hydrostatic slipper bearing capacity of axial piston pump

Hydrostatic slipper was often used in friction bearing design, allowing improvement of the latter's dynamic behavior. The influence of thermal effect on hydrostatic slipper bearing capacity of axial piston pump was investigated. A set of lumped parameter mathematical models were developed based on energy conservation law of slipper/ swash plate pair. The results show that thermal equilibrium clearance due to solid thermal deformation periodically changes with shaft rotational angle. The slipper bearing capacity increases dramatically with decreasing thermal equilibrium clearance. In order to improve the slipper bearing capacity, length-to-diameter ratio of fixed damper varies from 3.5 to 8.75 and radius ratio of slipper varies from 1.5 to 2.0. In addition, the higher slipper thermal conductivity is useful to improve slipper bearing capability, but the thermal equilibrium clearance is not compromised.

Estimation of Axial Pile Bearing Capacity According to Shear Strength Parameters of Soil

At pesent, it is very popular to estimate pile bearing capacity by use of empirical formula and physical indexes of soil provided in the design codes for civil construction in China. This paper attempts to apply mechanical indexes of soil and semi-empirical formulas, which are based on soil mechanical theories and were summarized and presented by Meyerhof in 1976, to calculate the axial pile bearing capacity. Loading test results of 24 single piles in Tianjin area have been collected and compared with the proposed calulation approach.

3D FE Analysis of Effect of Ground Subsidence and Piled Spacing on Ultimate Bearing Capacity of Piled Raft and Axial Force of Piles in Piled Raft

The effects of ground subsidence and piled spacing on axial force of piles in squared piled rafts were investigated using numerical analysis. Two cases of piled rafts in soft clay including case 1 (s = 2d) and case 2 (s = 4d) with s and d were piled spacing and piled diameter respectively were considered in this study. Undrained (without ground water pumping) and drained (with ground water pumping) conditions were applied in each case in order to evaluate variations of ultimate bearing capacity of piled raft and axial force of the piles in piled raft. The results showed that ultimate bearing capacity increased about 25% for undrained condition and about 32% for drained condition when piled spacing increased from 2d to 4d. In the same piled spacing, axial force of the piles increased about 9% for piled spacing of 2d and 7% for piled spacing of 4d when drained condition was applied. When piled spacing increased 2 times (2d to 4d), the axial force of piles increased about 7% for undrained condition and about 5% for drained condition.

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory

A new calculation method for axial load capacity of separated concrete-filled steel tubes based on limit equilibrium theory was proposed,which took into account the decrease of confinement effect by steel tube and the non-uniform distribution of ultimate stress in cored concrete.The accuracy of the analytical result is validated through running the numerical result by finite element method (FEM) and experimental data as well.The influences of the key parameters on the load capacity of the concrete-filled steel tube (CFST) was studied,including the separation ratio,concrete compressive strength,and steel strength.The results indicate that the load capacity of the tube increases with concrete strength and steel strength under the separation ratio less than 4%,while decreases with a higher separation ratio improved.

Prediction of Axial Capacity of Concrete-Filled Square Steel Tubes Using Neural Networks

The application of artificial neural network to predict the ultimate bearing capacity of CFST （ concrete-filled square steel tubes） short columns under axial loading is explored. Input parameters consiste of concrete compressive strength, yield strength of steel tube, confinement index, sectional dimension and width-to-thickness ratio. The ultimate bearing capacity is the only output parameter. A multilayer feedforward neural network is used to describe the nonlinear relationships between the input and output variables. Fifty-five experimental data of CFST short columns under axial loading are used to train and test the neural network. A comparison between the neural network model and three parameter models shows that the neural network model possesses good accuracy and could be a practical method for predicting the ultimate strength of axially loaded CFST short columns.

Axial Load Capacity of Cast in Place Piles from SPT and CPTU Data

This paper aims to deal with the assessment of axial load capacity for cast in place pile foundations, which are made by the earth drill method, by using the data taken from Standard Penetration Tests (SPTs) and Piezocone Penetration Tests (CPTUs). These tests were carried out as part of the investigation program for P.N.G. Terminal-Power Plant, near Semani beach, in Hoxhara marsh, in the western part of Albania. The design of axial load capacity of piles is based on empirical formula using SPT and CPTU values. This study presents the results of axial load capacity analysis of cast in place piles by different analytical calculation methods, which are based on in situ tests results, and also referring to the Building Standard Law of Japan. In the end of our work, differences between calculations methods by using different in situ tests results are shown in tables and graphs.

Response of carrying capacity of piles induced by adjacent Metro tunneling

Construction of tunnels in urban areas requires assessment of the impact of tunneling on the stability and integrity of existing pile foundations. We have focused our attention to the analysis of the carrying capacity of pile foundations provided by the impact of construction of urban tunnels on adjacent pile foundations, under the engineering background of the construction of the # 2 Line of the Guangzhou subway. It is carried out using a fast Lagrangian analysis of a continuum in a 3D numerical code, which is an elastoplastic three-dimensional finite difference model, to simulate the response of piles under the entire process of metro tunneling （deactivation of soil element and activation of the lining）. The adjacent stratum around the tunnel is classified into three regions： Zone Ⅰ （upper adjacent stratum of tunnel）, Zone Ⅱ （45°-upper-lateral adjacent stratum of tunnel） and Zone Ⅲ （lateral adjacent stratum of tunnel）. In each region one typical pile is chosen to be calculated and analyzed in detail. Numerical simulations are mainly conducted at three points of each pile shaft： the side-friction force of the pile, the tip resistance of the pile and the axial loading of the pile. A contrasting analysis has been conducted both in the response of typical piles in different regions and from computer calculated values with site monitoring values. The results of numerical simulations show that the impact on carrying capacity of the piles lies mainly in the impact of construction of urban tunnels on the side-friction forces and the tip resistance of piles. The impact differs considerably among the different strata zones where the pile tips are located. The complicated rules of side-friction force and tip resistance of piles has resulted in complicated rules of pile axial loading thus, in the end, it impacts the carrying capacity of pile-foundations. It is necessary to take positive measures, such as stratum grouting stabilization or foundation underpinning, etc, to deal with the carrying capacity and the settlement of pile-foundations. The results are of value to similar engineering projects.

Contact Force Distribution and Static Load-carrying Capacity of Large Size Double Row Four-point Contact Ball Bearing

Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance of bearing is first included is presented for determining the contact force distribution and static load-carrying capacity of a double row four-point contact ball bearing which is subjected to the combined radial,axial and overturning moment loadings.The relation between the negative axial clearance and the contact force distribution is analyzed.The static load-carrying capacity curves are established,and the effects of the changes in negative axial clearance,curvature radius coefficient of raceway groove and initial contact angle on the static load-carrying capacity are analyzed.The results show that,with the increase in the absolute value of negative clearance,the maximum contact load decreases first and then increases.The clearance values in the range of 0.2 mme0 mm have little effect on the static load-carrying capacity of bearing.With the increase in the curvature radius coefficient of raceway groove and the decrease in the initial contact angle,the static load capacity of bearing decreases.

局部锈蚀圆钢管混凝土短柱轴压承载力试验研究

钢管混凝土(CFST)在服役环境中被腐蚀,导致其钢结构承载力降低,严重威胁到结构的服役性能和使用寿命。首先,采用机加工车铣方法制作模拟局部锈蚀的人工缺陷,然后以钢管外表面局部环向贯通锈蚀位置、锈蚀钢管体积损失率、锈蚀外表面面积损失率(简称锈蚀面积损失率,下同)为试验参数,对45根局部锈蚀圆CFST短柱试件进行轴压承载力试验;其次,分析锈蚀位置、锈蚀钢管体积损失率、面积损失率和壁厚损失率对锈蚀试件承载力、刚度和延性的影响,揭示锈蚀CFST试件破坏机理和承载力退化机制;最后,针对局部锈蚀圆CFST短柱构件轴压承载力提出一个简化实用计算公式。研究结果表明:各试件具有类似的破坏特征,主要呈明显的腰鼓状破坏,且发生在锈蚀区;随着锈蚀钢管体积损失率增大,锈蚀CFST柱的承载力、刚度和延性均出现不同程度的降低;在锈蚀钢管体积损失率和面积损失率相同的情况下,就局部锈蚀位置影响而言,中部影响最大;就锈蚀程度表征参数影响而言,锈蚀钢管体积损失率影响最大,面积损失率次之,壁厚损失率最小;本文提出的简化实用公式可为圆钢管混凝土构件全寿命设计提供参考依据。

考虑结构空间约束的现浇楼盖梁跨中受弯性能试验

为研究结构空间约束导致现浇钢筋混凝土楼盖梁跨中受弯承载力超强的机制,以楼盖梁在结构中的空间位置和配筋率为变量,设计12根上部架立筋不伸入支座的楼盖梁试件并开展跨中受弯静力试验,并基于建立经典混凝土理论的试验方法进行了4根简支梁对比试验。对梁试件破坏形态、承载力、变形能力、轴向伸长进行研究,结果表明:楼盖梁试件承载力与按受弯构件计算承载力之比为1.57~2.77,与相应矩形简支梁试件和T形简支梁试件承载力相比均有较大提高,超强程度与配筋率成反比;与简支梁试件相比,楼盖梁试件跨中截面破坏形态未因轴压力而发生显著改变,但楼盖梁试件延性降低;楼盖梁试件轴向伸长随挠度的增大而增大。将楼盖梁视为压弯构件,提出根据楼盖梁试验峰值荷载确定相应轴力和弯矩的方法。计算结果表明,楼盖梁试件跨中截面压弯状态弯矩与受弯状态弯矩的比值为1.28~2.19。楼盖梁试件有限元数值模拟结果表明,随着楼盖梁截面包含的楼板范围增大,轴力沿梁跨分布趋于均匀。

泵站过流能力校核系统开发及应用

泵站长期运行阻力加大、出流能力减弱,影响城市排涝。基于Python编程语言和数字图像技术,开发了一套泵站过流能力校核评估系统,运用摄像机实时采集轴流泵电压表、电流表数据,同步采用超声波多普勒剖面仪、雷达水位计实时测量泵站出口流量和扬程。针对复杂流态、环境噪声干扰下流量数据偏差大的问题,建立了移动中值滤波法,并利用贝塞尔插值进行数据填充,有效提升了流量数据的准确性。实践应用于泵站出流能力校核,测得该泵站相同功率和相同扬程条件下出流能力均较理论值下降。

RPC外包方钢管混凝土柱轴压受力性能研究

为了研究活性粉末混凝土(Reactive powder concrete,RPC)外包方钢管混凝土柱的轴压受力性能,以RPC厚度和长细比为参数,对6根构件开展轴压试验研究,探讨该类组合柱的破坏模式、受力机理、套箍效应和承载力。试验结果表明:外层RPC可为内部方钢管混凝土柱提供较强的约束力,在受力后期套箍效应凸显。随着RPC厚度的增加,组合柱的承载力逐渐提高;随着组合柱长细比的增大,虽然其弹性刚度和承载力逐渐降低,但延性改善。采用ABAQUS软件建立RPC外包方钢管混凝土柱的有限元模型,分析RPC强度、RPC厚度、钢管强度等级、含钢率、内部混凝土强度和长细比等参数对组合柱承载力的影响规律,可得方钢管混凝土柱发挥系数的变化幅值为0.78~1.01。在试验研究、有限元参数分析和理论探讨的基础上,借鉴钢管混凝土结构技术规范,提出了RPC外包方钢管混凝土轴压短柱和长柱的承载力简化计算方法,公式计算值与已有数据样本吻合良好。

十字形钢管束自密实混凝土短肢剪力墙轴压性能研究

为研究十字形钢管束自密实混凝土短肢剪力墙的轴压受力性能,通过模型试验研究和ABAQUS数值模拟相结合的方法,对不同腔体数十字形钢管束自密实混凝土短肢剪力墙的轴压性能进行分析。首先,根据轴压试验结果对剪力墙的破坏形态和轴向荷载-应变曲线等轴压受力性能进行分析,提出轴压承载力计算公式。其次,建立剪力墙轴压有限元计算模型,将试验结果和模型计算结果进行对比以验证有限元模型的准确性。最后,根据有限元参数化分析结果验证并修正剪力墙轴压承载力计算公式。研究发现,剪力墙的轴向荷载-应变曲线在不同腔体数下具有相似的特征,表明其变形能力良好。在破坏过程中,钢管束对核心混凝土的约束作用显著,提高了试件的延性和承载能力,其中钢管束的破坏主要表现为多波鼓曲和焊缝开裂,尤其是在钢管束中部的1/4区域。此外,随着腔体数增加,剪力墙极限承载力提升,但其延性系数有所下降。本研究提出的简化公式与有限元分析结果的误差控制在10%以内,该公式可为工程设计应用提供理论借鉴。

钢筋锈蚀粘结削弱后轴心受压柱承载能力试验研究

通过去除钢筋周围粘结混凝土的方法来模拟钢筋锈蚀后粘结性能下降对柱抗压承载力的影响情况。研究发现:钢筋锈蚀程度对粘结力削弱的轴心受压柱的承载力影响较明显,在钢筋锈蚀不严重时,钢筋与混凝土的应变基本一致,柱破坏时两种材料强度能发挥出来;钢筋严重锈蚀时,混凝土应变滞后,柱破坏时混凝土的强度不能充分发挥出来,且钢筋锈蚀根数越多柱承载力下降越快;同时,随着粘结性能下降,柱破坏时裂缝的条数、长度及宽度都有所减少。根据试验研究结果,推导出粘结削弱轴心受压柱混凝土柱承载力计算方法。

轴向载荷下双金属机械复合管界面紧密度研究

为研究应用于油气田集输和海洋工程等领域的双金属机械复合管界面的紧密度特性,建立了液压成型及轴向载荷下双金属机械复合管力学模型,对比了梯形加载、递增式加载与脉动加载液压成型工艺对复合管界面紧密度的影响,探究了轴向载荷下成型压力与结构参数对复合管界面紧密度的影响规律。结果表明,脉动加载液压成型工艺与梯形加载、递增式加载加工工艺相比,管间残余接触压力提升45%,可以更好地保证双金属复合管成型的稳定性;提高成型后的残余接触压力,有助于增强复合管抗载能力;外基管壁厚对复合管承载力的影响最大;内衬管单独承受拉伸载荷时界面分离现象最明显,增加内衬管壁厚能延缓界面分离。

间断焊接包管加固圆钢管构件轴压极限承载力研究

为研究间断焊接包管加固杆件的轴心受压性能,设计了13组试件进行单调加载静力试验。对试件极限承载力、破坏模式、荷载-位移曲线和截面应变发展规律进行分析,对比了负载加固与非负载加固对试件极限承载力的影响。结果表明:包管构件的破坏模式可分为整体失稳破坏和内管外伸段强度破坏;包管构件内外管协同工作、共同受力,内管和外管都在屈服后发生整体失稳破坏;负载加固与非负载加固试件的极限承载力基本一致,相差2.2%,非负载加固试件与未加固试件相比,极限承载力最大提高了479.9%。根据试验结果对包管构件的ABAQUS有限元模型进行修正,并用该模型分析了各主要影响因素对包管构件极限承载力的影响规律。提出了包管构件极限承载力经验计算公式,且公式计算结果与试验结果吻合较好。

单板焊接空心球节点受拉承载性能研究

单板焊接空心球节点常用做弦支穹顶上部结构连接拉杆或拉索的节点,单板主要承受拉力并传递至焊接空心球,为了满足工程设计的要求,需对其受拉承载性能进行研究.通过试验,研究了不同参数的单板焊接空心球节点轴拉状态下的受力性能和破坏机理,建立有限元模型并进行验证,该模型能较好地反映单板焊接空心球节点轴拉性能,通过有限元模型参数化分析揭示了节点尺寸、加劲肋、单板尺寸等参数对其力学性能的影响规律,并提出单板焊接空心球轴拉承载力计算公式.研究结果表明:单板焊接空心球在轴拉作用下为应力集中导致的剪切强度破坏,破坏发生在单板端部与空心球连接处,表现为焊接空心球被撕裂;有限元应力云图得出破坏时沿着单板平面内拉力方向的剪应力起主要作用;单板焊接空心球节点的受拉承载力随单板宽度及空心球壁厚的增大而明显增大,空心球直径的增大会使承载力略有降低,单板的厚度增加使节点承载力略有提高,单板的高度对节点承载力的影响较小,空心球内设置加劲肋能使承载力提高至少20%;基于参数化提出的单板焊接空心球节点的受拉承载力计算公式能简便地计算出单板焊接空心球节点的承载力,相对误差在±15%以内,满足工程设计误差要求.研究工作可为今后外接单板的焊接空心球节点分析设计提供参考.

木塑空心柱轴压力学性能试验与有限元分析

为探究木塑复合材料用作低密度装配式建筑承重柱的可行性,通过材性测试和轴压试验评估共挤出木塑空心柱的轴压力学性能,并利用ABAQUS有限元分析软件模拟探究木塑空心柱壁厚、长细比和内置薄壁圆钢管壁厚对其极限承载力、变形能力和破坏模式的影响。模拟分析结果与试验测试数据高度一致,验证了模拟方法的有效性。试验研究表明,木塑空心柱主要通过局部压溃破坏,并表现出明显的弹塑性阶段。有限元分析结果表明,增加壁厚能提高木塑空心柱的初始刚度和极限承载力,其中8 mm厚度在成本、重量及承载能力方面具有最佳性价比。随着长细比的增加,木塑空心柱的承载力和刚度逐渐降低,破坏模式也从强度破坏转向失稳破坏。内置3 mm薄壁钢管显著增强了木塑空心柱的承载力和延性,其力学性能能够满足建筑对抗压承重构件的要求。

圆中空夹层不锈钢管水泥砂浆短柱轴压性能研究

海洋工程平台塔架结构中,圆形截面中空双钢管是主要受力构件,工程界十分关注其受压性能和耐腐蚀性能。为研究圆中空夹层不锈钢管水泥砂浆短柱的轴压力学性能,以外不锈钢管壁厚、内碳素钢管直径和是否含夹层水泥砂浆为试验变量,共设计了12个短柱试件。分析各试件的破坏情况、荷载-位移曲线、承载力、变形能力及应变特征,研究不同变量对极限承载力的影响规律。结果表明:试件破坏形态为外钢管端部或中部局部屈曲破坏;随着不锈钢管壁厚的增大,试件的轴压承载力近似呈线性增长;夹层水泥砂浆对试件力学性能影响较大,可有效提高试件承载力,抑制外不锈钢管的变形,提高试件延性;对于含夹层水泥砂浆的试件,承载力随空心率增大而减小,不含夹层水泥砂浆的试件,承载力随空心率增大而增大。根据国内外规范以及相关学者提出的理论公式,计算了试件的极限承载力,并与试验承载力进行了对比分析,给出了设计建议。

外包薄壁夹心钢-混组合管柱层间作用对其受压承载力的影响

为了研究外包薄壁夹心钢混组合管柱层间作用下的力学性能,建立了组合管柱有限元分析模型,通过库伦摩擦定义层间作用力,改变影响参数值,研究了轴压、偏压作用下组合管柱的力学性能。结果表明:当摩擦系数由0.2增大至0.4时,轴心受压柱与偏心受压柱极限承载力分别提高了1.06%、13.35%,由0.4增大至0.6时,分别提高了0.06%、13.61%;随着内外钢管与混凝土之间外力的增加,层间作用力和机械咬合力也相应地增加,增强层间作用力可以明显提高外包薄钢混凝土偏心受压组合管柱的极限承载力。