Bending and optimisation of an inflated braided beam

Two braided inflatable beams have been made that differ in the number of axial fibres that are placed parallel to the length, and in the angle at which the bias fibres are placed. Each beam consists of a silicone rubber bladder, two end caps and a dry carbon fibre braid placed over the silicone bladder. Experimental and theoretical analysis of the beams have been revealed that due to bending, the beams initially deflect in a linear manner like the Euler–Bernoulli beam model predicts. Once the stress in the axial fibres becomes zero, wrinkling occurs resulting in a significant loss of bending stiffness. The two beams that were tested were optimised for minimum deflection at a constant volume of fibres. The stiffest design has the maximum possible amount of fibres in parallel to the beam.     

长距离顶管管道的失稳分析

管道失稳是由于管道周围土体提供的抵抗力矩小于偏心顶推力而产生的扭转力矩,造成管节偏离设计轴线。分析了长距离直线顶管施工时管土之间的相互作用,认为管道在承受对角荷载时会产生转动力矩,当管道端部的最大土体反力超过土体承载力时土体产生破坏,造成管道整体失稳。提出了管道失稳时假定接头处为铰链的管土相互作用宏观模型。分析了传统曲线顶管施工中管土之间的相互作用,建立了首节管道和后续管节的受力模型及土体反力分布模式。采用考虑位移的土压力计算方法计算环向土压力,得出首节管道和后续管节最大土体反力的计算公式。对一个工程实例进行了计算,结果表明首节管道容易失稳。提出了长距离直线和曲线顶管施工防止管道失稳的控制措施。     

隧道施工扰动下管线变形三维预测方法及应用

本文研究隧道开挖对地下管线的影响,提出基于管线三维壳体仿真模拟的管线变形预测方法。考虑管线真实的薄壁结构,利用FLAC3D有限差分程序作三维壳体结构仿真模拟,把已知的土体变形以位移加载方式作用于管线,计算结果即为管线变形状态。通过该预测方法与梁结构弹性连续解法的对比计算,论述了壳体模拟用于低刚度管线的准确性,也验证了梁结构用于高刚度管线的可行性。实际工程中,按照实际管线的材质、几何尺寸和土体参数建模,把地表沉降实测数据作为已知量输入,即可预测管线受力变形情况。     

Parametric study of frost-induced bending moments in buried cast iron water pipes

While the features of frost susceptible soils have been examined in various studies, the mechanisms by which volume changes due to ground freezing can influence cast iron water pipes buried below the frost line have not been explained, and the hypothesis that frost-induced ground deformations can induce ring fractures due to longitudinal bending of these pipes has not been proven. Therefore, a parametric study employing three dimensional finite element analysis is reported, where the soil–pipe interaction associated with a pipe crossing under an intersection of a major arterial road with a residential street are examined. The arterial road is modeled as having non-frost susceptible sub-base and the local street is represented as having a lower grade pavement with frost susceptible sub-base. One specific frost loading case featuring both isotropic pore water expansion and orthotropic ice lens formation is modeled.The analysis demonstrates how volume changes due to ground freezing in soil strata above the buried pipe can induce bending moments sufficient to cause ring fracture. Changes in the relative axial stiffness of the pipe were found to have only a small effect on pipe moments. Decreases in the relative flexural stiffness of the pipe resulting from reductions in pipe modulus also had only a small effect on pipe deflections and normalized moments. Changes due to soil modulus had a significant effect on deformations, but little influence on moments. Decreases in pavement stiffness decrease pipe deflections and moments. Trench backfill conditions greatly affect deflection and moment. Reduction in burial depth from 2 m to 1.5 m increases deflections, and increases moments beyond the failure capacity of the grey, cast iron pipe considered in the study, and this computational result is directly supported by field evidence.     

Nonlinear aeroelastic response of slender wings based on Wagner function

This paper presents a method for nonlinear aeroelastic analysis of Human Powered Aircraft (HPA) wings. In this type of aircraft there is a long, highly flexible wing. Wing flexibility, coupled with long wing span can lead to large deflections during normal flight operation; therefore, a wing in vertical and torsional motion using the second-order form of nonlinear general flexible Euler–Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic theory based on Wagner function is used for determination of aerodynamic loading on the wing. Combining these two types of formulations yields the nonlinear integro-differentials aeroelastic equations. Using the Galerkin's method and modes summation technique, the governing equations will be solved by introducing an iterative numerical method to predict the aeroelastic response of the problem. The obtained results for a test case are compared with those of linear study which shows good agreement for speeds less than the flutter speed, but the nonlinear model shows limit cycle oscillations for the wing beyond the flutter boundary.     

盾构双隧道不同开挖顺序及不同布置形式对管线的影响研究

在离心模型试验中同时考虑隧道开挖所致地层损失效应和质量损失效应,研究不同开挖顺序及不同布置形式下双隧道开挖对管线的影响规律。同时采用基于地层损失比的位移控制有限单元法对离心模型试验及其他4组拓展工况进行分析,其中土体本构模型采用考虑土体小应变特性的HP(Hypoplasticity model)模型,并将试验结果与已有的解析方法进行对比。研究结果表明,双隧道不同开挖顺序及不同布置形式对地表沉降、管线沉降、管线弯曲应变的影响显著;管线存在所产生的"遮拦"效应对管线正上方地表沉降的影响程度随着自由场最大地表沉降的增加而逐渐加剧;双隧道开挖所致管线沉降的主要影响区域为-1.2D_T~1.2D_T;实际工程中应加强浅埋后继隧道开挖时管线工作性状的监测工作,且不应简单采用叠加原理对不同施工工序及不同布置形式的双隧道开挖所致地表沉降、管线沉降及管线弯曲应变进行预测,应合理考虑后继隧道开挖所致土体的累计剪切应变及上覆隧道的遮拦效应对管–土相对刚度的影响。     

既有管线下盾构施工地层沉降监测和位移加载数值分析

针对深圳地铁下穿电缆隧道的实例,通过采用位移加载法模拟隧道开挖效应和弹性地基梁理论分析管土相互作用,提出将地铁上方的既有隧道视为大管径管线考虑,分析了地铁左线施工引起的地层响应,并借助相关控制标准对电缆隧道的安全性作出评价,分析结果表明:数值计算结果与实测数据吻合较好,电缆隧道也处于安全状态,可为相关类似工程研究提供借鉴。     

Stability loss of thin-walled cylindrical tubes, subjected to longitudinal compressive forces and external corrosion

The paper is devoted to investigation of stability loss of thin-walled elastic circular cylindrical pipes subjected to simultaneous action of longitudinal compressive forces and uniform corrosion from outside. The pipe is treated as a thin closed elastic circular cylindrical shell which can be described within Kirchhoff–Love approximation. The critical time of stability loss of the pipe is found, using the upper critical load value for static stability loss of the pipe, not subjected to corrosion, and the law of corrosion rate. Numerical results were obtained for pipes, made from steel and aluminum with different initial wall thickness.     

地层沉陷中埋地HDPE管道力学状态及模型试验分析

地层沉陷致埋地HDPE管道事故频发,主要原因之一是地层沉陷过程中所诱发的管道附加应力和变形剧增,从而导致管道破坏。已有研究成果大多集中于固定尺寸沉陷区域管道与周围土体力学特性的分析,尚无相关理论预测沉陷发展过程中管道力学响应特征变化规律。利用自制室内足尺大型模型试验系统,以粗砂为管道开挖沟槽回填料,通过调整模型箱底板的下沉模拟地层沉陷形成过程,研究埋地HDPE双壁波纹管道的受力变形特性及其上覆回填料土体的沉降分布规律。试验结果表明:1地层沉陷过程中HDPE管道的竖向变形符合修正高斯分布曲线;2随着土体沉陷的发展,管道顶部土压力随之增大,且试验管道顶部的土拱率由0.7增大到2.05,呈现出明显负土拱效应;3对于相同抗弯刚度管道,土体沉陷变形所致管道附加变形随管道上覆土层厚度的减小而减小;4随着管道抗弯刚度增加,埋地管道对于土体的沉降抑制作用愈加明显。     

浅析直埋热力管道泄漏的主要原因

主要阐述了热力直埋管网泄露的主要影响因素,指出泄漏主要是由热力耦合作用、管土相互作用、管道材料本身特性、流体本身特性、地质条件、管道周围环境以及施工质量上的因素引起的,并提出了相应的预防措施,以使泄漏降低到最低限度。     

跨逆断层埋地管线受力特性的管土效应分析

断层错动引起的地表永久性大变形是导致埋地管线破坏的重要因素之一,埋地管线的断层反应特性受到土介质和管线材料等因素的影响,本文以逆断层位错作用下的无缝直埋地管线为研究对象,基于ABAQUS有限元分析软件,建立埋地管线-土介质的三维有限元数值分析模型,利用非线性接触描述管-土接触状态,考虑初始地应力条件的影响,对跨逆断层埋地管线的受力特性进行数值模拟分析,依据计算结果主要分析了位错量、管线材料、管-土相互作用、土介质、管径等参数对埋地管线断层反应的影响效应,并得到:管-土介质接触效应是管线断层反应分析中不可忽视的影响因素,粘聚力较小、硬度较低的中硬土介质中的埋地管线抗断层性能较优等有益结论。     

软土地区大口径玻璃钢夹砂顶管顶力监测分析

玻璃钢夹砂管因其重量轻、耐腐蚀、摩阻系数小、管道和接口抗渗强度高等优点,在城市给排水管道的顶管施工中得到越来越多的应用.通过现场测试与分析研究了上海软土地区大口径玻璃钢夹砂顶管的顶力特性.结合背景工程两个试验段对玻璃钢夹砂顶管的顶力进行了现场监测,并通过对顶进过程中的管壁土压力测试分析了顶管外壁摩阻力及摩擦系数,获得软土地区玻璃钢夹砂顶管顶力计算的经验公式,为今后同类工程的顶力设计计算提供更加准确有效的方法.     

考虑泥浆触变性和管土接触特性的顶管摩阻力公式

顶进力是顶管工程设计和施工的重要参数,而顶管侧摩阻力对顶进力起控制作用,其大小主要受管土接触和管浆接触特性影响。为了更加准确地计算顶管摩阻力,假设隧洞孔壁在泥浆压力作用下保持稳定,管道周围同时存在管土接触和管浆接触,采用协调表面Persson接触模型分析管土接触特性,得出考虑接触压力分布影响的管土摩阻力;然后利用半无限弹性体中柱形圆孔扩张理论分析注浆压力对泥浆套厚度的影响,并结合泥浆触变性和流体力学平行平板模型计算管浆摩阻力。在此基础上考虑管道与隧洞的相对位置,同时将管道顶进时的滑动摩擦阻力作为下限值,顶管重启动时的静摩擦阻力作为上限值,总结出直线和曲线顶管摩阻力公式。通过与工程实例数据对比,结果表明该计算公式下限值与实测值最接近,证明其适用性。     

Improvement in accuracy of the finite element method in analysis of stability of Euler–Bernoulli and Timoshenko beams

The problem of buckling of the Euler–Bernoulli and Timoshenko beams is analyzed by the finite element method. Significant improvement in accuracy of the method is obtained by replacing the discontinuous function of the bending moment related to the approximation of the eigenfunction obtained by FEM by a “smoothed” function in the Rayleigh quotient. The smoothed function is obtained by fitting the discontinuous one using the least square technique.     

受腐蚀埋地式混凝土管管周土压力的计算模式初探

作用在埋地管管周的土压力是管道和周围土体相互作用的结果,埋地式污水混凝土管道受腐蚀后其变形能力将有所变化,对管周土压力也会产生相应的影响。论文首先讨论了腐蚀作用对管道截面整体刚度以及管土相对刚度的影响;根据腐蚀程度对管壁弹性模量的变化进行定量化折减,进而将其刚度的变化反映到混凝土管道相对刚度影响系数上,结合前人的计算模型,推导了反映受腐蚀埋地式混凝土管管周的土压力计算公式。研究可为对埋地混凝土污水管道腐蚀的后续研究提供基础资料及参考,对管道设计及其使用过程中的力学状态分析具有一定的指导意义。     

巨型-子结构控制体系抗震特性分析

建立空间相互作用模式下的杆系模型,利用大型通用有限元软件ANSYS的功率谱密度分析(PSD)功能对巨型-子结构控制体系在随机地震作用下的动力响应进行计算与分析,并对子结构相对抗侧力刚度采用多个采样点。在主结构刚度不变的情况下,采取合理的子结构刚度能有效控制体系的前各阶振型,获得理想的减振效果;不合理的子结构刚度不但不能获得控制效果,还会放大地震作用。     

再生水管道管材的经济技术比较

根据实践经验,对球墨铸铁管、钢塑复合钢管及PE给水管进行了管道水头损失及管材费用、防腐性能、物理性能等方面的比较,通过对比研究,得出钢塑复合钢管用于再生管道工程中具有较好的防腐、节能效果,值得推广应用。     

大口径新型顶管力学行为现场试验研究

通过对新型预应力钢筒混凝土顶管(JPCCP)开展现场试验,得到了在施工荷载、水土压力等三维荷载作用下顶管各部位的应变时程响应;同时也获得了顶进过程中管–土接触应力时程变化。根据对数据的分析,得出预应力钢筒混凝土顶管具有较大的纵向抗压刚度,而纵向抗拉刚度不足。由于预应力的效应,内层混凝土与中间层混凝土能够承受较大的环向拉应力。通过对管节的纵向受力分析,计算出管–土平均摩阻力随顶进距离的变化规律,结合施工记录得出平均摩阻力随顶进距离先增大后减小,最小值为1.27 k Pa;同时,施工顶进间隔越短,平均摩阻力越小。此外,实测结果表明,管–土接触应力对管节运动较为敏感,最大瞬时值可达500 k Pa;施工结束后,接触应力沿管周分布并不对称或均匀,但与实测管节环向应变分布对应。     

跨断层地下管线振动台模型试验研究Ⅱ:试验成果分析

针对跨断层地下管线进行振动台模型试验研究。试验中将钢管埋设在一个盛装砂土、可以模拟走滑断层错动作用的模型箱中,研究地下管线在承受断层错动时应变的分布规律和管周动土压力变化规律,并考察地下管线与断层的夹角以及管内水体的影响。试验结果表明:在跨断层地下管线中,管-土系统本身的动力效应的影响较小,可以忽略不计,而管内液体可能有较大的影响,不可忽略;在无法避开断层区域的情况下,地下管线最好与断层垂直;管线的最大应变发生在断层附近一定距离的位置;管-土动力相互作用及其变化规律对管道响应影响很大。     

大口径输水管道的止推设计

广州市西江引水工程是广州市的生命线工程,其管径大、压力高,且双管同槽敷设。主管材采用预应力钢筒混凝土管(PCCP),由于弯头处双管推力很大,使得弯头处的止推设计成为保证整个输水系统安全的关键因素,也是工程设计的重点和难点之一。对几种常用的止推形式进行分析,并针对西江引水工程推力大、用地紧张、工期短等具体情况,最终确定了钢管外包混凝土的止推形式。对该种止推形式的设计进行了介绍,可供类似工程参考。