Seismic Fragility Assessment of LNG Pipe Rack Accounting for Soil-Structure-Interaction

Abstract

The increasing momentum for Natural Gas exploitation in Europe and worldwide constitutes Liquified Gas terminals indispensable links of energy supply network. Infrastructures of this kind should be resilient against the earthquake hazard and thus designed accounting for as much as possible sources of uncertainty such as modelling issues, analysis methods, seismic input selection, soil effects and others. To date, research efforts have not assessed the response of pipe racks sufficiently, let alone the interaction between the rack and piping system and analysis methods of the past have proved to be neither adequate nor efficient towards evaluating the earthquake hazard potentiality. Further, soil-structure-interaction has not been incorporated into a fragility analysis framework; albeit it is considered as a critical parameter since midstream and downstream facilities are usually rested on alluvial deposits. In the present work, a supporting RC rack is analysed through a 3D finite element model in the nonlinear regime both as coupled and decoupled vis-à-vis a piping system. The fragility functions are evaluated for structural components and limit states in the global and meso-scale, through the Incremental Dynamic Analysis (IDA) considering far-field conditions. In the end, the SSI is encountered accounting for linear and nonlinear soil, and soil effects are demonstrated by the fragility curves. It is inferred that the fragility of the rack soars considerably by the piping system boundary conditions in the coupled case and the SSI has detrimental impact, and thus should be accounted, particularly, for industrial structures that are located at coastal sites.