Evidence from past earthquakes suggests that damage inflicted to buried natural gas (NG) pipelines can cause long service disruptions, leading to unpredictably high socioeconomic losses in unprepared communities. In this review paper, we aim to critically revisit recent progress in the demanding field of seismic analysis, design and resilience assessment of buried steel NG pipelines. For this purpose, the existing literature and code provisions are surveyed and discussed while challenges and gaps are identified from a research, industrial and legislative perspective. It is underscored that, in contrast to common belief, transient ground deformations in non-uniform sites are not necessarily negligible and can induce undesirable deformations in the pipe, overlooked in the present standards of practice. It is further highlighted that the current seismic fragility framework is rich in empirical fragility relations but lacks analytical and experimental foundations that would permit the reliable assessment of the different parameters affecting the expected pipe damage rates. Pipeline network resilience is still in a developing stage, thus only few assessment methodologies are available whereas absent is a holistic approach to support informed decision-making towards the necessary mitigation measures. Nevertheless, there is ground for improvement by adapting existing knowledge from research on other types of lifeline networks, such as transportation networks. All above aspects are discussed and directions for future research are provided.

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.

Despite the breadth of the available finite element codes for seismic analysis and assessment, the associated complexity in use and the generality in orientation are likely to increase the epistemic uncertainty involved in the models, particularly in nonlinear analysis procedures. Thus, it is of interest to develop tools for improving the reliable use of existing structural engineering software. This paper aims to present the capabilities of Build-X, a recently developed knowledge-based system tailored to the prediction of the seismic response of 3D buildings. This expert system features a simple visual user interface that supports the structural engineer throughout the structural configuration of a building, providing expert suggestions as to critical modelling decisions, and automations that increase the reliability of the analysis and accelerate the pre-processing stage. Build-X is linked with OpenSees, a widely used script-based freeware for seismic analysis of structures, which is utilized to perform the core finite element analysis. Post-processing tasks are easy to handle through the graphical engine of the system developed. A verification study demonstrates the efficiency of the system and reliability of the results generated, pointing to the way in which Build-X may serve as a useful tool for the seismic analysis of newly designed buildings and the assessment of existing ones at reduced computational cost and modelling uncertainty.

Steel gas pipelines may be subjected to buckling failure under large compressive straining, caused by seismically induced ground deformations. This paper further elaborates on the buckling response of this type of networks, through the presentation of representative results from a series of axial compression static analyses that were conducted on segments of steel gas pipelines. Above ground and embedded segments of diverse radius to thickness ratios (R/t) were simulated by means of inelastic shell elements. The trench of embedded pipelines was modelled using solid elastic elements, while an advanced contact model was used to simulate the pipe-soil interface. Salient parameters that affect the axial response, including the internal pressure and the existence of imperfections on the segment, were considered in this study. In line with previous evidence, the results reveal a reduction of the axial response of the pipe segment with increasing levels of internal pressure. In parallel, internal pressure leads the limit stresses to occur at progressively higher axial deformations, while limit loads computed for embedded pipelines are higher compared to those predicted for equivalent above ground pipelines, as a result of the soil confinement.

This paper reports on results from a series of 1-g, reduced-scale, shake table tests of a 216mlong portion of an onshore steel gas transmission pipeline embedded in horizontally layered soil. A set of first-order set of dynamic similitude laws was employed to scale system parameters appropriately.Two sands of different mean grain diameter and bulk density were used to assemble a compound symmetrical test soil consisting of three uniform blocks in a dense-loose-dense configuration. The sandpipe interface friction coefficients were measured at 0.23 and 0.27. Modulated harmonic and recorded ground motions were applied as table excitation. To monitor the detailed longitudinal strain profiles in the model pipe, bare Fiber Bragg Grating cables were deployed. In most cases, the pipe response was predominantly axial while bending became significant at stronger excitations. levels. Strain distributions displayed clear peaks at or near the block interfaces, in accord with numerical predictions, with magnitudes increasing at resonant frequencies and with excitation level. By extension to full-scale, peak axial strain amounted to approximately 10 -3 , a demand half the yield strain, but not negligible given the low in-situ soil stiffness contrast and soil-pipe friction.