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Bellows joint is a critical part of an underground pipeline system, which can undergo severe damage such as breaking, crushing, and bending under a strong earthquake. In our research work, finite element analysis (FEA) of the bellows joint was studied using LS-DYNA. Single convolution and multi-convolution bellows joints applied with different loadings were investigated. Force – displacement curve, plastic strain distribution and bending moment – angular displacement curve were obtained. Furthermore, low frequency cyclic experiment on 4-convolution bellows joints was conducted and the results from the experiment were compared with the results from FEA. The load capacity of the multi-convolution bellows joint was almost the same as the single convolution bellows joint, and the energy absorption increased with the number of the convolution linearly. [ABSTRACT FROM AUTHOR]

Damage to buried pipelines caused by local amplification of seismic ground motion in highly nonuniform grounds is not yet fully understood. The development of methods to evaluate the amplification of ground motion in complex ground structures is thus desirable. Here, we report large-scale nonlinear seismic ground response analysis using a 3D nonlinear finite element method (FEM) and attempt to reproduce observed seismic ground motion. We also discuss the strain amplification processes and their effects on buried pipelines in detail. The findings are expected to aid in improving the seismic resistance of buried pipelines. [ABSTRACT FROM AUTHOR]

Analyses on the basis of seismic array records have confirmed that spatially distributed earthquake ground motions are neither fully coherent nor independent, but partially coherent. It has not yet been fully addressed how the partially coherent nature of seismic ground motions affect the seismic response of underground pipelines. In this paper, the impact of auto power spectrum density, pipe cross-sectional radius, and wall thickness, local effect, and coherency effect on pipeline responses are analyzed by calculating the longitudinal and lateral seismic responses of continuous pipelines in a homogeneous medium using a pseudoexcitation algorithm of the random vibration theory. A numerical integration technique is developed by converting infinite integration into a series with limited terms. Sufficient precision is achieved when integration steps are sufficiently small. The method provides a simplified way for practical professionals to analyze response of underground pipelines to earthquakes. [ABSTRACT FROM AUTHOR]

Seismic ground faulting is a severe hazard for continuous buried pipelines. Over the years, researchers have attempted to understand pipeline behavior mostly via numerical models such as the finite element method. The lack of well-documented field case histories of pipeline failure due to faulting along with the costly and complex facilities needed for full-scale experimental simulation make a centrifuge-based method to determine the behavior of pipelines subject to faulting the best method to verify numerical approaches. This paper presents results from four centrifuge tests investigating the behavior of continuous buried steel pipelines that were subjected to reverse faulting. The axial and bending strains induced in a pipeline are presented. Also investigated is the influence of factors such as faulting offset, burial depth, and pipe diameter on the axial and bending strain of pipelines and on the ground soil failure and pipeline deformation pattern. Finally, the initial strain at the wrinkling point of the pipe under reverse faulting is studied and compared with theoretical values. It was found that the pipe deformation mechanism and damage type are significantly altered by variations in pipe diameter, burial depth, and pipe section slenderness ratio (diameter to thickness ratio). Increasing the diameter and burial depth of a pipe changes the deformation mechanism from beam buckling to wrinkling. The wrinkling strains from these tests are in good agreement with the findings of Hall and Newmark. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper a semi-analytical methodology for a nonlinear stress–strain analysis of buried steel pipelines at active fault crossings is presented and verified. The developed model introduces a number of critical refinements to the existing methodologies which extend the application area of analytical models in pipeline design. In particular, a strike-slip and normal-slip fault crossings can be analyzed taking into account material and large displacement nonlinearities, nonlinear pipe–soil interaction. The proposed model is verified against the results by other authors and numerical results, obtained with the finite element method. [ABSTRACT FROM AUTHOR]

The article focuses on the performance of ductile-iron pipelines at locations vulnerable to earthquake shaking or seismic activity. With strong resilient pipe and flexible joints due to technological advances, ductile-iron pipe has become the pioneer in water and sewer piping for distribution and transmission mains up to 64 inches in diameter. It highlights three conditions that resulted to earthquake damage including shaking, fault conditions, and ground failure.

Seismic response of underground pipelines is usually calculated by wave propagation theory, in which spatially full coherence of seismic ground motions is assumed. The analysis of data recorded at dense instrument arrays has confirmed the partial coherence of seismic ground motions at different stations. The effect of the partial coherence of seismic ground motions on underground continuous pipeline is not very clear. In this paper, seismic responses of underground continuous pipeline in both longitudinal and lateral directions in uniform medium are studied by the pseudo-excitation method in random vibration theory, and then the impacts of locality effect and coherence effect on underground continuous pipeline are analyzed respectively. The results show that it may be unsafe without consideration of the partial coherence of seismic ground motions, and different coherence models lead to different results. It is suggested that the partial coherence of seismic ground motions should be considered, and the coherence models should be chosen cautiously. [ABSTRACT FROM AUTHOR]

A welded joint generally has heterogeneity of strength, material, and fracture toughness. It is important to understand the characteristics of the strength and fracture of welded joints while considering the heterogeneous effect. In particular, the material behavior becomes more complicated when the welded joint with strength heterogeneity is subjected to dynamic rapid loading; for example, the welded heat-affected zone of pipeline steels is softened and welded underground pipelines are affected by a rapid ground sliding in an earthquake. In this paper, the characteristics of the strength and fracture of an undermatched joint under dynamic loading are studied by round-bar tension tests and thermal elastic-plastic analyses. The results show that the strength and fracture characteristics of the undermatched joints should be evaluated based on the effects of the strain rate and the temperature, including the temperature rise during dynamic loading. The tensile strength and the yield stress of the undermatched joints increase with the strain rate and with the decreasing temperature. The strength of the undermatched zone approaches that of the base metal when the thickness of the undermatched zone becomes smaller, and it does not depend on the strain rate. Finally, it is found that the stress-strain distribution affects fracture characteristics such as ductile-to-brittle transition behavior. The fracture characteristics are explained and predicted from the results of stress-strain relations obtained by numerical analysis. [ABSTRACT FROM AUTHOR]