Can a buried gas pipeline experience local buckling during earthquake ground shaking?

Abstract

The damage potential of spatially variable seismic ground motion on buried pipelines has long been confirmed by field evidence, but it is still debatable whether transient seismic loads can be truly detrimental to the pipeline integrity. In the absence of systematic scrutiny of the effects of local site conditions on the seismic behaviour of such structures, this study presents a staged approach to numerically investigate the elastic-plastic buckling response of buried steel natural gas pipelines subject to transient differential ground motions arising from strong lateral site inhomogeneities. The first stage involves the study of 2D linear viscoelastic and equivalent-linear site response for the case of two sites and the resulting seismic demand in terms of longitudinal strains for input motions of various intensities and frequency content. The influence of key problem parameters is examined, and the most unfavourable relative ground deformation cases are identified. In the second stage of analysis, the critical in-plane ground displacement field is imposed monotonically on a near-field trench-like 3D continuum soil model encasing a long cylindrical shell model of the pipeline. Next, the performance of the buried pipeline is assessed under axial compression. The impedance contrast between the laterally inhomogeneous soil profiles is shown to govern the amplitude of induced elastic strains, which are maximized for low-frequency excitations. It is also demonstrated that peak axial strains along the pipeline considering equivalent-linear soil behaviour under strong earthquake motion can be as much as two orders of magnitude larger than their linear counterparts, as a result of the severe, spatially variable moduli degradation. It is finally shown that the seismic vibrations of certain inhomogeneous sites can produce appreciable axial stress concentration in the critically affected pipeline segment near the material discontinuity, enough to trigger coupled buckling modes in the plastic range. This behaviour is found to be controlled by pronounced axial force-bending moment interaction and is not accounted for in code-prescribed limit states.

A critical review on the vulnerability assessment of natural gas pipelines subjected to seismic wave propagation. Part 1: Fragility relations and implemented seismic intensity measures

“…The lack of relevant damage reports and therefore of relevant fragility relations for continuous pipelines has been attributed by some researchers to their better performance, compared to the segmental pipelines, when subjected to seismicallyinduced transient ground deformations. However, several studies have demonstrated that under particular circumstances, transient ground deformations may result in appreciable strains on continuous pipelines, which in turn may lead to damages as well (O'Rourke M.J., 2009;Psyrras and Sextos, 2018;Psyrras et al, 2019).…”

“…Local buckling of buried pipelines has been a subject of early and recent studies (e.g. Chen et al, 1980;Lee et al, 1984;Yun and Kyriakides, 1990;Psyrras et al, 2019) and is further examined in the second part of this paper. Beam-mode or 'upheaval' buckling leads to an upward bending of the pipe, which in some cases may even seen as a reveal of the pipe out of the ground surface.…”

“…However, statistically it is more likely for a pipeline to be subjected to transient ground deformations rather than seismically induced permanent ground deformations. Additionally, studies have demonstrated that pipelines embedded in heterogeneous sites and/or subjected to asynchronous ground seismic motions are likely to be affected by appreciable deformations and strains due to transient ground deformations, which in turn may lead to damages on the pipeline (Psyrras and Sextos, 2018;Psyrras et al, 2019). Along these lines, this study focuses on the transient ground deformation effects.…”

A critical review on the vulnerability assessment of natural gas pipelines subjected to seismic wave propagation. Part 2: Pipe analysis aspects

“…An alternative approach is to simulate the imperfection by means of a geometric stress-free perturbation in the initial geometry and mesh of the examined shell (e.g. Yun and Kyriakidis, 1990;Psyrras at al., 2019).…”

“…For the latter cases, a stress-free, biased axisymmetric imperfection was assumed at a short zone of 1.0 m, which was set at the middle of the segment. The imperfection was defined following Paquette and Kyriakides (2006) and Psyrras et al (2019), having a maximum amplitude of 10 % of the pipe wall thickness (i.e. w/t = 0.1).…”