城市地下综合管廊内高压输电线对钢制管道电磁干扰的研究

近些年国内外管廊运行中发生的事故层出不穷,尤其是随着电力电缆、燃气、热力管线入廊,使得管廊风险因素大大提高,而廊内管道受电磁干扰引起管道破坏并导致人员伤亡是城市地下综合管廊安全运行的最主要安全隐患。为了掌握廊内管道受高压输电线电磁干扰的影响因素及规律,给管廊的建设提供技术支撑,通过专业分析软件CDEGS模拟研究了廊内高压输电线对廊内管道电磁干扰的影响。结果表明：管道上感应电压和感应电流随着高压线电压和土壤电阻率的增大而增大,随着管道与高压线之间距离增大先急速减小后缓慢减小,管道规格对感应电压和感应电流的影响不大,感应电压随着防腐层电阻率增大先增大后趋于稳定,感应电流随着防腐层电阻率增大先减小后趋于稳定。     

地下综合管廊抗爆性能及加固方法研究

为了解地下综合管廊的极限抗爆性能，基于LS-DYNA商用软件，建立了精细化数值计算模型，分析了内部燃气爆炸荷载作用下管廊结构的动力响应特征和受荷破坏全过程，揭示了其失效破坏机理。分析结果表明：当爆炸超压为80～140 kPa时，管廊结构墙缝、顶板跨中和边墙跨中位置出现裂缝；当爆炸超压为160 kPa时，边墙出现弯剪破坏；当超压达到180 kPa时，顶板在跨中位置明显破坏；当超压达到200 kPa后，结构发生倒塌破坏；基于超压峰值和结构破坏关系建立了管廊损伤预测方法，标定了管廊的损伤预测等级；提出了2种结构加固方法，将管廊结构抗爆性能提升了17.5%、146%,该加固方法为同类管廊提供了借鉴。     

带楼板RC连梁抗震性能试验研究

该文通过9个RC连梁试验研究交叉斜筋、楼板和连梁轴力对连梁抗震性能的影响,并考察了楼板的损伤情况。试验结果表明:试件破坏模式基本为剪切破坏和弯曲剪切破坏;布置交叉斜筋的试件屈服承载力和极限承载力都有提高,极限承载力提高20%以上;布置楼板的试件屈服承载力提高6%~12%,试件受剪切破坏控制导致楼板对极限承载力的影响较小;楼板裂缝在试件转角达到0.25%时基本达到正常使用极限状态最大裂缝宽度限值0.2 mm,楼板损伤较严重;连梁在加载过程中承受压力作用,轴压比基本在5%~10%。     

竖向荷载作用下飘浮体系斜拉桥极限承载能力与失效模式分析

提出采用塑性极限分析法研究竖向荷载作用下大跨飘浮体系斜拉桥的极限承载力和失效模式。基于塑性极限分析的相关假定并结合基本机构证明了该方法应用于斜拉桥失效分析的可行性,结合飘浮体系单塔斜拉桥推导了极限承载力计算公式并分析对应的失效模式,通过优化方法-内点法获得斜拉桥塑性极限荷载及其对应失效模式,并与OpenSEES有限元分析结果进行了对比分析。结果表明:竖向荷载作用下,主梁在拉索屈服强度较小时为整体性破坏,反之则为局部性破坏;相比拉索而言,主梁屈服强度对斜拉桥破坏的影响则正相反;拉索锈蚀在降低斜拉桥极限载荷系数的同时也改变其倒塌失效模式;相比于有限元法,塑性极限分析法简便且易操作,可用于研究竖向荷载作用下飘浮体系斜拉桥的极限承载能力与失效模式,且能够快速有效评估结构参数变化对其失效行为的影响。     

钢管混凝土哑铃形截面拱空间受力性能试验研究

进行了钢管混凝土哑铃形拱的面外受力性能试验,与钢管混凝土单圆管拱的面外试验进行了对比,采用经试验验证的有限元模型进行了面外极限承载力的参数分析。研究结果表明:模型拱面内以受压为主,而面外则是以跨中受面外弯矩为主,模型拱最后发生了整体面外失稳破坏,破坏时在跨中与拱脚截面材料进入塑性;模型拱的受力状态中,面外弯矩所占比重最大,约为71%~78%;其面外极限承载力小于面内极限承载力,下降的幅度与面内外荷载比、面外刚度以及截面类型有关;腹腔高度和宽度的增大引起哑铃形截面刚度和极限承载力增大,腹腔高度增大33%或宽度增大50%,模型拱的面外承载力增加约11%~17%或10%~14%;钢管混凝土哑铃形截面拱面外承载力计算方法的构筑中面外抗弯刚度是决定性参数,同时要综合考虑面内抗弯刚度和抗扭刚度的影响;而分支屈曲荷载与极限承载力的比值分析表明,实际工程中钢管混凝土哑铃形截面拱面外屈曲系数大于4是有安全保障的。     

钻爆法地铁隧道开挖对地下管线的影响

钻爆法地铁隧道施工对临近管线的影响目前研究较少。利用FLAC3D软件施加爆破荷载,研究地铁隧道开挖时周边管线的应力位移的变化。通过改变地表振速来体现爆破荷载的变化,研究不同爆破强度下管线应力位移的变化。同时在研究中,考虑管线与隧道平行及管线与隧道垂直两种位置关系。研究结果表明:由于管线对地层沉降的抵抗作用,当管线与隧道垂直时,管线的竖向位移小于二者相平行时的,但拉压应力大于二者相平行时的;地表振速在1.2².4cm/s时,管线内拉压应力增长迅速,当振速达到2.7cm/s,管线拉应力并未达到接头填料拉应力限值;振速在1.452.4cm/s时,管线内拉压应力增长迅速,当振速达到2.7cm/s,管线拉应力并未达到接头填料拉应力限值;振速在1.45².0cm/s范围内,管线位移增大明显,振速达到2.7cm/s后,管线竖向位移超过工程限值;随着地表振速的增大,管线竖向位移斜率不断增大。管隧平行时,振速增大到2.3cm/s后,位移斜率增长速度加快。     

TC4钛合金板厚度对其撞击失效特性影响研究

为了揭示TC4钛合金板抗撞击性能与失效模式随厚度的变化规律及机理,采用ABAQUS/Explicit有限元软件建立平头弹撞击不同厚度靶板的模型,对弹体撞击不同厚度靶板进行计算。通过对比数值仿真与撞击实验结果,验证仿真模型的有效性。研究结果表明,靶板的主要失效模式、耗能机制、弹道极限随其厚度增加会发生改变,靶板厚度存在对应的转折值。对于TC4钛合金薄板,当靶板厚度比较小时,靶板拉伸撕裂破坏占主导作用。但是,当靶板厚度比较大时,靶板主要失效模式是局部剪切破坏。当靶板厚度小于4 mm、大于8 mm时,弹道极限速度随靶板厚度的增加而增加;当厚度为4~8 mm时,弹道极速度变化不明显。     

不同拘束条件下P92钢高温蠕变裂纹扩展速率的有限元模拟

基于蠕变损伤力学,仿真了蠕变裂纹扩展过程。用ABAQUS软件模拟研究了试样几何形状和宽度不同的两种面内拘束条件对P92钢在650℃时蠕变裂纹扩展(CCG)速率的影响,并进行了试验验证。仿真结果表明:试样几何形状和宽度对CCG速率的影响与载荷水平(C*)有关;在低载荷水平区内,C(T)试样的拘束水平大于SEN(T)试样,并且对应的CCG速率较大;在中载荷水平区,随着试样宽度的增大,裂纹尖端拘束和CCG速率增大;在高载荷水平区,CCG速率基本不受面内拘束(试样几何形状、宽度)条件的影响;在条件相同的情况下,试样宽度拘束水平大于试样几何形状。试验结果表明,试验与有限元分析(FEA)的蠕变裂纹扩展结果相符合。     

碳纤维增强环氧树脂复合材料螺栓连接结构在拉伸载荷下损伤过程的声发射分析

采用声发射技术对不同几何尺寸的碳纤维增强环氧树脂复合材料（CFRP）螺栓连接结构在静力载荷下破坏行为进行了试验研究,比较了不同几何构型下的连接结构的破坏行为与声发射信号之间的映射关系。采用声发射技术对结构损伤过程中的声发射信号进行全程采集与转换,结合CFRP螺栓结构的载荷-位移曲线和宏/细观破坏形貌,分析了幅值、熵曲线和Andrews曲线与破坏行为之间的关系。结果表明:挤压与剪切破坏试件的载荷-位移曲线均呈现出较明显的塑性特征。结构发生挤压和剪切破坏时,声发射信号以中幅值信号为主,并伴随少量高幅值信号;结构发生拉伸破坏时对应的幅值为中幅值信号。根据熵曲线特征将CFRP连接结构破坏过程分为四个阶段,在损伤演化阶段发生纤维断裂、分层等失效模式,在结构失效阶段以分层失效为主。基于Andrews曲线分析得到挤压和拉伸失效模式在损伤演化阶段会出现多种损伤类型,剪切失效模式在结构失效阶段会出现多种损伤类型。      

静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度

为探究静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度，以湿法缠绕工艺制备中厚玻璃纤维增强树脂基复合材料(GFRP)圆柱耐压壳结构模型，对其初挠度进行测试，并开展静水压破坏试验，分析了结构的极限承载能力、应变响应和破坏模式。基于实测初挠度及破坏模式，建立含缺陷复合材料圆柱壳的非线性分析有限元模型，同时考虑壳体几何缺陷及承压过程中的复合材料面内损伤，编制ABAQUS接口子程序USDFLD，对模型的损伤过程进行数值模拟，获得静水压下含缺陷中厚复合材料圆柱壳的渐进失效过程，并与试验结果对比验证。研究表明：在静水压下中厚GFRP圆柱壳结构在破坏前载荷几乎呈线性增加，最终破坏模式为材料的压缩破坏，整体屈曲破坏模式不明显。考虑结构的几何缺陷和材料损伤演化后，采用非线性有限元模拟得到的壳体极限强度与试验结果吻合良好，可以作为预测含缺陷中厚复合材料圆柱壳极限强度的方法。采用该方法对影响中厚复合材料圆柱耐压壳极限强度的关键参数进行了研究，为深海复合材料耐压壳的研究设计提供参考。     

Gas transmission pipeline failure probability estimation and defect repairs activities based on in-line inspection data

Degradation of an underground pipeline during its service life leads to reduction of the pipe wall thickness. Periodic in-line inspections are performed by onshore pipelines operators to detect corrosion anomalies and size their depth and width. In the paper, a simple analytical method of burst pressure calculation for a straight pipeline repaired with a composite sleeve was investigated. Repair activities after an in-line inspection of a gas transmission pipeline were considered in this research to assess the pressure of a pipe with a flaw reinforced with a different number of layers of a fiber-based polymer sleeve. Det Norske Veritas criteria and formulation of a limit state function were applied to determine the burst pressure and corresponding failure probability of a pipeline with a large number of single and non-interacting part-wall defects. The Monte Carlo method was selected for estimation of pipeline failure probability and cumulative failure probability due to the external corrosion considering fluid pressure fluctuations in dynamic flow effects with respect to statistical distribution of input parameters were examined in this research. The proposed novel 3-step approach was validated on the real data collected from an onshore high pressure gas pipeline DN 700, MOP 5.5 MPa provided by two magnetic flux leakage inspections repeated at an interval of twelve years. A probabilistic methodology was applied to evaluate the part-wall external corrosion defects and their deterministic linear growth with time and repair activities on gas transmission pipelines were analyzed. The results of this study shall help maintenance engineers solve the problems of an optimal strategy in reliability-based high pressure gas pipelines management.     

管道承插式接口轴向力学性能试验研究与数值模拟

通过球墨铸铁供水管线承插式接口抗拉静载力学性能试验,分析管道接口轴向的拉伸力学性能和破坏模式,并建立相应管道接口受力分析的有限元数值模型。在外部无覆土、加压注水条件下,对球墨铸铁输水管道承插式接口进行拟静力拉拔试验,模拟其在地震作用等往复荷载下的轴向受力与变形特征。试验结果表明,加载方式以及管道内部水压等对接口的轴向抗拉力学性能和破坏方式的影响不大,抗拉极限位移达到60 cm。基于OpenSees计算平台建立管道接口有限元模型,并对试验结果进行了模拟,结果表明建立的管道接口有限元模型能够较好地模拟管道接口在轴向往复荷载作用下的刚度退化和耗能等力学特征,为埋地管道在复杂轴向荷载作用下的受力分析和性能评估提供了必要的试验数据和计算模型。     

Failure pressure of medium and high strength pipelines with scratched dent defects

It is very important in engineering design and integrity assessment of pipeline to accurately predict its failure pressure, especially for the pipeline with mechanical damages. This paper numerically investigates the failure pressure of medium and high strength pipelines with scratched dent which is on the outer surface of the pipe. Pipe materials of two different grades are chosen in the analysis which represent medium and high strength steel, respectively. Failure pressure of an intact pipeline with fixed ends is derived analytically. On the basis of the maximum plastic strain failure criterion put forward by previous scholars, failure pressure of finite element models containing dent and scratch defects is determined. Parametric studies are carried out to obtain the influencing rule of the dimensions of dent and scratch. The effects of scratch length and depth on failure pressure with various dent depths are obtained. Finally, a formula is fitted for predicting the failure pressure of pipelines with scratched dents on the basis of finite element results. Compared to burst test data from literature, the proposed formula is proved to be reasonable.     

Determination of the position of an underground pipeline using the results of measurements of its magnetic field strength

The results of an experiment to determine the position of an underground pipeline using its magnetic field strength when there are other underground systems (cables and pipelines) present, situated side by side, are presented. It is shown that the excitation of a current in the pipe by a current in a wire, grounded at the ends, occurs as a result of magnetic coupling between the wire and the pipe. At a frequency of the exciting current higher than 1 kHz, currents occur in the other nearby pipelines lines which lead to ambiguity and errors in determining the route of the pipeline.     

Pipeline failures in corrosive environments – A conceptual analysis of trends and effects

Pipeline corrosion is a major challenge facing many oil and gas industries today because of the enormous downtime associated with corrosion related failures. Fatigue stress initiation in pipelines has been attributed to corrosion defects whose growth is enhanced by cyclic loading caused by the operating pressure of the transported fluids. This work reviews the concept of oil and gas transmission pipeline failures in corrosive environment by highlighting the corrosion mechanisms, dominant stress corrosion cracking trends, hydrogen induced cracking and predominant models for burst pressure estimation. Fatigue stress failure trends of corroding pipelines were also explained whilst describing some pipeline manufacturing processes that increases the susceptibility to fatigue stress failure. Optimization framework for pipeline integrity assurance against corrosion fatigue failures was also shown to incorporate different steps that includes – strategic policy initiation, policy implementation, information analysis and reviews and implementation actions.     

To refurbish or replace steel water pipelines,that is the question

Underground steel water pipelines that are not suitably coated and lined will corrode after a certain period of time, externally where the steel is in contact with the soil and internally where the steel is in contact with water. Such corrosion results in the thinning of the pipeline walls, reduction in the mechanical strength due to this thinning and finally possible failure of the pipeline. The integrity of older pipelines can be investigated by conducting a series of tests on the pipeline, both destructive and non-destructive, to determine the condition of coating and lining of the line pipe, the mechanical properties, and the extent of the thinning of the pipe walls. The results of these tests are used to determine whether refurbishment or replacement of the pipeline is the most viable option. This paper reports one such case study.     

基于ANSYS/LS-DYNA的竖井掏槽延时爆破研究

为了探究小间距地下在建构筑物爆破施工对既有地下结构的影响,以米仓山竖井及隧道工程为例,从竖井掏槽孔延时爆破的角度,采用有限元软件ANSYS/LS-DYNA,针对既有隧道的降振效果进行了一系列的数值模拟。模拟结果表明:当多个掏槽孔同时起爆时,爆破地震波的传播易受传播介质及传播距离的影响,且爆破地震波具有明显的主振段;延时爆破可实现多个爆破波不同程度的叠加消能情况;当延时时间为2 ms,即为主振周期的一半时,既有隧道降振效果十分显著;延时时间大于主振周期时,降振效果同样明显,但主振区持时也相应拉长,可能会为隧道带来长持时的塑性破坏;此外,竖井掏槽时间的确定应结合结构的破岩效果进行考虑。     

在役石油化工管道腐蚀现状及修复对策

由于受外部环境影响以及加工原油不断劣质化,导致管体内外腐蚀日趋严重,介绍了石油化工管道腐蚀现状、腐蚀原因以及修复对策。分析了碳纤维复合材料补强修复技术对石油化工腐蚀管道修复的适用性、可行性。碳纤维补强技术在石油化工腐蚀管道的成功在线应用,表明其在管道的完整性管理和长周期运行中发挥着重要的作用。     

Failure resistance of drilling rig casing pipes with an axial crack

Working conditions of casing pipes in drilling rigs can significantly influence the initiation and development of damage in the material, and therefore also the safe service of the entire system. In this work, an integrity assessment of a pipe with initial defect (machined surface crack) is presented. The position of this defect is on the external surface; unlike transport pipes, where internal surface is often endangered due to the contact with the fluid, casing pipes are also often exposed to damages at the external surface. A pipe segment exposed to internal pressure is examined experimentally and numerically, using the finite element method. Experimental setup included tracking of crack mouth opening displacement (CMOD) values, as well as J integral. Criteria for pipe failure are determined on the finite element (FE) models of the pipe; fracture initiation and plastic collapse are considered as failure mechanisms. Several 3D models with different crack sizes are evaluated. 2D plane strain models are also examined, to determine the applicability limits of this simplified approach. Integrity assessment criteria for the analysed geometries are discussed. Assessment of fracture resistance of the pipeline material is also considered in this work. Besides the standard SENB specimens, Ring specimens cut from the pipe are tested, and the results are compared. Both specimen geometries are modelled using local approach to fracture, by application of the micromechanical Complete Gurson model (CGM), developed by Z.L. Zhang. It is shown that the Ring specimens have similar fracture conditions under bending load as SENB specimens. Since they are much simpler to fabricate from the pipe than standard specimens, it is concluded that they can be used for assessment of fracture of the pipes with axial cracks.     

移植隧道对股骨力学性能的影响

该文应用Mimics 8.1软件由膝关节螺旋CT数据重构3D股骨模型。基于该模型依据单束、双束韧带重建手术的要求,建立了膝关节正常股骨、含单移植、双移植隧道股骨的三种近似三维有限元模型。根据股骨在关节屈伸中承受载荷的性质提取压缩、弯曲和扭转三种作用力,分别加载到上述三种有限元股骨模型上,进行有限元仿真。该文提出截面应力比较法,从股骨截面应力云图中提取最大有效应力值与最大第一主应力值为指标来评定隧道对股骨承载性能的影响,通过对比分析表明:无论采用前交叉韧带重建的哪种方法,在正常压缩、弯曲和扭转的三种负载下,隧道对ACL重建后的截面应力分布状态影响不明显,对股骨最大有效应力值的影响较弱(应力变化量≤5.06%),对股骨第一主应力值的影响也较小(变化量≤6.85%)。总之,ACL重建移植隧道对股骨承载应力的影响较小。在临床手术中医生对股骨隧道的视点只需放在起止点的准确选取上。该文提出的截面应力比较法丰富了ACL重建术后的股骨力学性能评定的技术与方法。