Nonlinear stochastic seismic analysis of buried pipeline systems

In this paper, a nonlinear stochastic seismic analysis program for buried pipeline systems is developed on the basis of a probability density evolution method (PDEM). A finite element model of buried pipeline systems subjected to seismic wave propagation is established. The pipelines in this model are simulated by 2D beam elements. The soil surrounding the pipelines is simulated by nonlinear distributed springs and linear distributed springs along the axial and horizontal directions, respectively. The joints between the segmented pipes are simulated by nonlinear concentrated springs. Thereafter, by considering the basic random variables of ground motion and soil, the PDEM is employed to capture the stochastic seismic responses of pipeline systems. Meanwhile, a physically based method is employed to simulate the random ground motion field for the area where the pipeline systems are located. Finally, a numerical example is investigated to validate the proposed program.     

Centrifuge modeling of buried continuous pipelines subjected to normal faulting

Seismic ground faulting is the greatest hazard for continuous buried pipelines.Over the years,researchers have attempted to understand pipeline behavior mostly via numerical modeling such as the finite element method.The lack of well-documented field case histories of pipeline failure from seismic ground faulting and the cost and complicated facilities needed for full-scale experimental simulation mean that a centrifuge-based method to determine the behavior of pipelines subjected to faulting is best to verify numerical approaches.This paper presents results from three centrifuge tests designed to investigate continuous buried steel pipeline behavior subjected to normal faulting.The experimental setup and procedure are described and the recorded axial and bending strains induced in a pipeline are presented and compared to those obtained via analytical methods.The influence of factors such as faulting offset,burial depth and pipe diameter on the axial and bending strains of pipes and on ground soil failure and pipeline deformation patterns are also investigated.Finally,the tensile rupture of a pipeline due to normal faulting is investigated.     

Permanent earthquake‐induced actions in buried pipelines: Numerical modeling and experimental verification

Buried pipelines are often constructed in seismic and other geohazard areas, where severe ground deformations may induce severe strains in the pipeline. Calculation of those strains is essential for assessing pipeline integrity, and therefore, the development of efficient models accounting for soil‐pipe interaction is required. The present paper is aiming at developing efficient tools for calculating ground‐induced deformation on buried pipelines, often triggered by earthquake action, in the form of fault rupture, liquefaction‐induced lateral spreading, soil subsidence, or landslide. Soil‐pipe interaction is investigated by using advanced numerical tools, which employ solid elements for the soil, shell elements for the pipe, and account for soil‐pipe interaction, supported by large‐scale experiments. Soil‐pipe interaction in axial and transverse directions is evaluated first, using results from special‐purpose experiments and finite element simulations. The comparison between experimental and numerical results offers valuable information on key material parameters, necessary for accurate simulation of soil‐pipe interaction. Furthermore, reference is made to relevant provisions of design recommendations. Using the finite element models, calibrated from these experiments, pipeline performance at seismic‐fault crossings is analyzed, emphasizing on soil‐pipe interaction effects in the axial direction. The second part refers to full‐scale experiments, performed on a unique testing device. These experiments are modeled with the finite element tools to verify their efficiency in simulating soil‐pipe response under landslide or strike‐slip fault movement. The large‐scale experimental results compare very well with the numerical predictions, verifying the capability of the finite element models for accurate prediction of pipeline response under permanent earthquake‐induced ground deformations.     

跨断层水泥管试验的有限元分析

在考虑管道的材料非线性和几何非线性、管土相互作用的非线性和管道接口非线性的基础上,建立了由管体梁单元、三向土弹簧单元和接口单元组成的埋地非连续管道在断层位移作用下的有限元模型,并以美国密歇根大学Junhee等(2010)所做的跨断层水泥管试验为原型进行了模拟分析。有限元结果给出的水泥管最终变形、接口转角、接口位移与实验结果基本一致,表明本文提出的跨断层埋地非连续管道抗震计算的有限元分析方法具有一定的合理性。有限元结果和试验结果都表明,在逆冲断层作用下,水泥管的破坏主要是因为在管道接口处的轴向压力和弯矩的耦合作用,在断层附近的管道接口承受了较大的转动和压缩位移。本文所提出的分析方法可推广到埋地非连续管道在其它永久地面变形作用下的有限元分析。     

地震动多点差异输入对架空管道地震响应影响研究

架空管道由于地震波传递、地震动衰减以及场地不均匀产生各支撑点地震动差异,为了研究这种差异对架空管道地震响应的影响,通过有限元软件ADINA建立架空管道有限元模型,利用MATLAB软件编写具有相干效应的人工地震波,计算分析了多点地震动相干函数法输入、行波输入与一致输入下地震响应。结果表明:①随着视波速的增加管道轴向应变变小,有接近一致激励情况的趋势;②同一相干函数模型,考虑和忽略场地效应,管道轴向应变最大值存在差异;不同相干函数模型,管道轴向应变最大值也存在差异。结论认为,如果场地比较均匀且管段较短,可采用行波法进行地震输入;长柔管道应采用相干法进行地震响应分析,场地不均匀的长柔管道,应同时考虑场地效应。     

Pipe–soil interaction and pipeline performance under strike–slip fault movements

The performance of pipelines subjected to permanent strike–slip fault movement is investigated by combining detailed numerical simulations and closed-form solutions. First a closed-form solution for the force–displacement relationship of a buried pipeline subjected to tension is presented for pipelines of finite and infinite lengths. Subsequently the solution is used in the form of nonlinear springs at the two ends of the pipeline in a refined finite element model, allowing an efficient nonlinear analysis of the pipe–soil system at large strike–slip fault movements. The analysis accounts for large strains, inelastic material behavior of the pipeline and the surrounding soil, as well as contact and friction conditions on the soil–pipe interface. The numerical models consider infinite and finite length of the pipeline corresponding to various angles β between the pipeline axis and the normal to the fault plane. Using the proposed closed-form nonlinear force–displacement relationship for buried pipelines of finite and infinite length, axial strains are in excellent agreement with results obtained from detailed finite element models that employ beam elements and distributed springs along the pipeline length. Appropriate performance criteria of the steel pipeline are adopted and monitored throughout the analysis. It is shown that the end conditions of the pipeline have a significant influence on pipeline performance. For a strike–slip fault normal to the pipeline axis, local buckling occurs at relatively small fault displacements. As the angle between the fault normal and the pipeline axis increases, local buckling can be avoided due to longitudinal stretching, but the pipeline may fail due to excessive axial tensile strains or cross sectional flattening. Finally a simplified analytical model introduced elsewhere, is enhanced to account for end effects and illustrates the formation of local buckling for relative small values of crossing angle.     

Finite element analysis of buried steel pipelines under strike-slip fault displacements

The present paper investigates the mechanical behavior of buried steel pipelines, crossing an active strike-slip tectonic fault. The fault is normal to the pipeline direction and moves in the horizontal direction, causing stress and deformation in the pipeline. The interacting soil–pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behavior and special conditions of contact and friction on the soil–pipe interface. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80), the paper focuses on the effects of various soil and pipeline parameters on the structural response of the pipe, with particular emphasis on identifying pipeline failure (pipe wall wrinkling/local buckling or rupture). The effects of shear soil strength, soil stiffness, horizontal fault displacement, width of the fault slip zone are investigated. Furthermore, the influence of internal pressure on the structural response is examined. The results from the present investigation are aimed at determining the fault displacement at which the pipeline fails and can be used for pipeline design purposes. The results are presented in diagram form, which depicts the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. A simplified analytical model is also developed to illustrate the counteracting effects of bending and axial stretching. The numerical results for the critical strain are also compared with the recent provisions of EN 1998-4 and ASCE MOP 119.     

跨断层隔震管道分析

埋地管道在断层错动作用下的内力分析及其抗震措施一直是生命线工程的一个重要问题与研究热点。对地下管道在断层错位下的响应计算,取得的成果较多,比较经典的有Newmark-Hall方法和Kennedy方法。后来又出现基于壳模型的简化方法,如高田至郎提出的简化计算方法等。相对来讲,关于管道抗震措施的研究成果较少。本文提出一种抗震措施,进行了基于壳模型的有限元动力数值模拟,并与4种松到中密场地土条件下的埋地管道断层错位响应进行对比分析。计算结果表明,本方法中三种长度管道的最大轴向拉应变远小于埋地管道的最大轴向拉应变,而且最大轴向压应变亦不大。     

Intensity measures for the assessment of the seismic response of buried steel pipelines

To estimate the demand of structures, investigating the correlation between engineering demand parameters and intensity measures (IMs) is of prime importance in performance-based earthquake engineering. In the present paper, the efficiency and sufficiency of some IMs for evaluating the seismic response of buried steel pipelines are investigated. Six buried pipe models with different diameter to thickness and burial depth to diameter ratios, and different soil properties are subjected to an ensemble of 30 far-field earthquake ground motion records. The records are scaled to several intensity levels and a number of incremental dynamic analyses are performed. The approach used in the analyses is finite element modeling. Pipes are modeled using shell elements while equivalent springs and dashpots are used for modeling the soil. Several ground motion intensity measures are used to investigate their efficiency and sufficiency in assessing the seismic demand and capacity of the buried steel pipelines in terms of engineering demand parameter measured by the peak axial compressive strain at the critical section of the pipe. Using the regression analysis, efficient and sufficient IMs are proposed for two groups of buried pipelines separately. The first one is a group of pipes buried in soils with low stiffness and the second one is those buried in soils with higher stiffness. It is concluded that for the first group of pipes, \(\sqrt {{\text{VSI}}[\upomega_{1} ({\text{PGD}} + {\text{RMS}}_{\text{d}} )]}\) followed by root mean square of displacement (RMS_d) are the optimal IMs based on both efficiency and sufficiency; and for the second group, the only optimal IM is PGD²/RMS_d.     

穿越克孜尔逆冲断层的输气管道抗震分析

输气管道作为1种薄壁壳体结构,逆冲断层引起的管道压缩变形容易使其破坏。本文以大北南疆输气管道工程为例,探讨了穿越克孜尔逆冲断层的输气管道地震安全问题。在确定管道穿越处的断层倾角、设防断层位错量、表征管土相互作用的土弹簧参数以及钢管容许应变等参数后,采用壳有限元方法,分析了穿越克孜尔逆冲断层的输气管道变形反应。分析结果显示,管道在逆冲断层作用下以压缩应变为主,管道内的最大轴向压缩应变的幅值随着交角的减小而减小。在通过探槽等方法确定断层活动位置后,该管道若以小于或等于11°的交角通过克孜尔断裂,断层引起的最大轴向压缩应变和拉伸应变均在管道相应的容许应变范围内,满足相关规范的抗震要求。     

地震断层作用下的埋地管道等效分析模型

地震作用下,活动断层附近的埋地管道易发生强度屈服、局部屈曲或整体失稳等形式的破坏,建立准确、高效的埋地管道在断层作用下的计算模型,对管道的抗震设计和震后安全状态评估具有重要的实用价值。本文采用非线性弹簧模拟远离断层处埋地管道的反应,基于管土之间小变形段管道处于强化阶段,提出一种改进的管土等效分析模型,进一步减小了管土之间大变形段的分析长度,从而提高了有限元分析效率。该模型采用ALA推荐的方法计算管土间的滑动摩擦力,可以考虑土体种类的影响;用Kennedy方法确定管道的计算长度。通过与精确模型比较,验证了管土等效模型的合理性和有效性。     

基于振动台模型试验的高落差埋地管道地震响应研究

为研究高落差埋地管道的地震响应,进行了高落差埋地管道振动台模型试验和有限元数值模拟,探讨管道径厚比、管道倾角、地震波入射角、地震动峰值加速度和管道埋深对高落差埋地管道地震响应的影响规律。试验结果与数值模拟结果符合较好。研究结果表明,在入射角0°的地震波作用下,高落差埋地管道轴向应变峰值随着管道径厚比的增大而增大;在一定管道倾角范围内,管道轴向应变峰值随着管道倾角α的增大而增大;当地震波入射角度从0°变化到60°时,管道上下表面的轴向应变减小,侧面的轴向应变增大;管道应变随着地震动峰值加速度和管道埋深的增加而增大;相同地震作用下,管道最大轴向应变出现在下弯管1/3处附近。     

Effects of seismic wave propagation upon buried pipelines

The behaviour of long straight buried pipelines subjected to seismic wave propagation is investigated. Well-known relationships for determining upper bounds for the axial strain and curvature in the pipeline as well as relationships for relative displacement and rotation at the pipeline joints are discussed. The assumption that the seismic excitation can be modelled as a travelling wave having a shape which remains unchanged as it traverses the pipeline is examined in detail. It is shown that this assumption is unconservative when the effective propagation velocity of the seismic waves with respect to the pipeline is such that the actual time lag (separation distance between points divided by effective propagation velocity) is less than a ‘cross-over’ time lag. Cross-over time lags for 22 pairs of ground displacements recorded during the 1971 San Fernando Earthquake are presented in this paper. Finally, methods for estimating the propagation speed of the seismic waves along or with respect to the pipeline are discussed.     

Seismic damage to segmented buried pipelines

Seismic damage to segmented buried pipelines is investigated in this paper. Information on their performance during past earthquakes is reviewed briefly. An analytical model for evaluating the response of long straight runs of segmented buried pipelines to seismic wave propagation is presented. It takes into account the non-linearity as well as the variability of the system characteristics. Also, results from laboratory tests by others are used to establish the relative joint displacement which leads to leakage. These two elements are combined to predict the damage ratio (number of leaks per kilometre) for cast iron pipes with lead caulked joints subject to a joint pull-out failure mode.     

跨越断层埋地管线地震反应数值分析

跨越断层埋地管线在地震中的破坏是非常严重的,地震本身和管土相互作用体系中都存在很多不确定性因素,所以管线在断层运动过程中反应比较复杂。本文利用有限元理论和数值模拟手段,建立了管土作用模型,采用非线性接触问题研究方法详细地分析了管线由断层运动而产生的反应,对影响管线的各种因素进行了分析,包括位错量、跨越角度、断层运动形式、埋设深度、初始轴向力、断层裂缝宽度、填覆土质和管径。通过研究,得到一些初步结论。     

Pipe–soil interaction for segmented buried pipelines subjected to dip faults

This paper describes an investigation of pipe–soil interaction equations suggested by currently used pipeline seismic design codes and the applicability of these equations to segmented pipelines. The results of computer‐aided analyses were compared to results obtained in full‐scale experiments on a segmented ductile iron pipeline 93 mm in diameter and 15 m in length. The pipeline was installed 600 mm below the ground surface in a sandy soil compacted to two different subgrade reaction values. The type of fault considered was a reverse fault with an intersection angle of 60° with the pipeline, and the fault movement was a total of 350 mm in three same steps in the fault trace direction. The findings of this study demonstrate the necessity of considering the nature of soil behavior in pipe–soil interaction equations and the effects of connection joints on the integrated response of pipelines to fault‐induced ground deformations. A new combination of equations constituting a direction‐wise selection from among the equations proposed by currently used guidelines is introduced as a new series to describe pipe–soil interaction for segmented pipelines and is verified using the results of full‐scale experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

穿越逆冲断层的埋地管道非线性反应分析

穿越逆冲断层的埋地管道在地震作用下,容易发生局部屈曲或整体失稳等形式的破坏,研究逆冲断层作用下的埋地管道地震反应规律,对管道抗震设计及施工等具有重要的意义。本文将埋地管线及周围土体从半无限地球介质中取出,分别以空间薄壳单元和实体单元进行离散,采用非线性接触力学方法模拟管、土之间的滑移、分离及闭合现象;采用线性位移加载模拟断层的错动,考虑了系统初始应力状态的影响,对土体未开裂前的管土相互作用系统进行了拟静力数值分析;分析了位错量、土体刚度、埋设深度、径厚比及跨越角度对埋地管道反应的影响,得出了一些有益的结论。     

2D numerical investigation of segmental tunnel lining under seismic loading

Segmental tunnel linings are now often used for seismic areas. However, the influence of segment joints on the segmental lining behavior under seismic loading has not been thoroughly considered in the literature. This paper presents a numerical study, which has been performed under seismic circumstance, to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The proposed model allows studying the effect of the rotational joint stiffness, radial stiffness and the axial stiffness of the longitudinal joints. The numerical results show that a segmental lining can perform better than a continuous lining during earthquake. It has been seen that the influence of the joint distribution, the joint rotational stiffness, the joint axial stiffness, Young׳s modulus of the ground surrounding the tunnel, the lateral earth pressure factor and the maximum shear strain should not be neglected. Some important differences of the segmental tunnel lining behavior under static and seismic conditions have been highlighted.     

穿越走滑断层海底管道局部屈曲研究及应变响应预测

海洋地震频繁且海底土体环境复杂,当地震导致断层土体发生永久变形后,穿越断层的海底埋地管道也将受迫发生变形。为确定变形后的管道能否正常工作,需根据实际工况对其进行应变响应预测。首先通过有限元计算软件ABAQUS建立管道与走滑断层的三维实体模型,模拟管-土间的接触作用并通过等效边界方法修正模型,得到管道局部屈曲破坏形式及应变分布情况。然后,通过调整有限元模型参数对断层交角、管道工作内压、管道径厚比对管道极限塑性应变的影响进行敏感性分析,定性分析不同敏感性因素对穿越走滑断层海底管道应变响应的影响。最后,在数值模拟数据的基础上通过MATLAB软件利用基于遗传算法优化的BP神经网络实现对管道应变响应的精确预测。结果表明:穿越走滑断层管道在发生局部屈曲时,可根据轴向压缩应变突变现象确定管道局部屈曲时对应的断层位移,并且断层交角、管道工作内压和管道径厚比都会对跨断层管道应变响应产生影响。     

横向非一致地震激励下埋地管道的动力响应分析

为研究埋地管道在地震激励时管-土相互作用的动力响应问题,研发双向层状剪切连续体模型土箱,建立管G土相互作用有限元分析模型,对横向非一致地震激励下埋地管道地震响应进行数值模拟分析,并与试验结果进行对比.结果表明:数值模拟和振动台试验结果中的管道应变峰值均呈现出沿管道中间大两端小的现象,管道中间应变峰值最小达到两端的1．6倍左右;管道加速度、 土体加速度峰值均随着加载等级的提高而增大,涨幅愈加明显,多峰频率由0~10Hz逐渐向10~ 20Hz频域扩散,管道运动更为自由;土体位移随着加载等级的提高呈现逐级增大的现象,在加载等级增加到0．4g 时位移曲线斜率减小,土体非线性表现明显.数值模拟和振动台试验对比分析的结论表明数值模拟分析的合理性和试验结果的可靠性,为研究横向非一致激励对埋地管道地震响应的影响提供了依据.