This report is one of a series of reports documenting the methods and findings of a multi-year, multi-disciplinary project conducted by the Pacific Earthquake Engineering Research Center (PEER) with the Lawrence Berkeley National Laboratory (LBNL) and funded by the California Energy Commission (CEC). The overall project is titled “Performance-based Earthquake Engineering Assessment Tool for Natural Gas Storage and Pipeline Systems” henceforth referred to as the “OpenSRA Project.”
The overall goal of the OpenSRA Project is to create an open-source research-based seismic risk assessment tool for natural gas infrastructure that can be used by utility stakeholders to better understand state-wide risks, prioritize mitigation, plan new gas infrastructure, and help focus post-earthquake repair work.
The project team includes researchers from LBNL, UC Berkeley, UC San Diego, University of Nevada Reno, the NHERI SimCenter at UC Berkeley, and Slate Geotechnical Consultants and its subcontractors Lettis Consultants International (LCI) and Thomas O’Rourke. Focused research to advance the seismic risk assessment tool was conducted by Task Groups, each addressing a particular area of study and expertise, and collaborating with the other Task Groups.
This report is the product of Task Group D: Performance of gas storage and pipeline system surface infrastructure. The scope of this report is to describe the numerical analysis performed on surface natural gas components and subsystems and subsequent generation of seismic fragility curves in support of the OpenSRA software. Components analyzed included common fittings used in surface subsystems, namely welded steel elbows and tee joints. To this end, numerical models of these fittings were first created in the high-fidelity finite element analysis software Abaqus and their cyclic behavior validated against results from the experimental program presented in Pantoli and Hutchinson (2025). Subsequently, Abaqus was used to predict the response results of these fittings under varied boundary and loading conditions. Phenomenological (lumped) element material properties were then derived for the suite of fittings tested and modeled within Abaqus. These lumped models were integrated within numerical models of two types of surface subsystems and analyzed using the software OpenSees. The two surface subsystems of interest were: 1) the wellhead and piping (WTP) subsystem and 2) the vertical pressure vessels (VPV) subsystem. The dynamic properties of these two subsystems were validated via comparison with low amplitude modal impact (tap) experiments on real systems in the field as well as complementary high fidelity finite models. The OpenSees models were then subjected to a suite of scaled earthquake motions and these response results used to develop seismic fragility curves.
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