Seismic Assessment of Pipe Racks Accounting for Soil-Structure Interaction

The research on the seismic assessment of pipe racks accounting for coupling and soil-structure interaction effects is still scarce. Common industrial practice overlooks critical design aspects due to the insufficiency of current codes that might result in over-conservative or unsafe design. This work addresses the nonlinear analysis of a petrochemical plant steel pipe rack accounting for dynamic interaction with horizontal vessels and pipelines. Soil-structure interaction was evaluated both on pipe rack and pipelines in terms of interstorey-drift ratio and stress-strain response. An attempt was made for correlating the ratio with piping strain to make comparisons with common acceptance criteria for building structures, since code provisions do not address currently limit state design concept for pipe racks. Additionally, seismic fragility curves along with 95% confidence intervals were evaluated for different intensity measures and were used as a tool to demonstrate that the soil deformability could act as an isolation mechanism for pipelines. The increase of pipe rack displacements was an additional impact of soil, though, it was not as much profound as on the seismic response of the pipelines. The detailed structural assessment through extensive nonlinear dynamic analyses demonstrated that the return period of exceedance of pipe rack and pipelines limit state, considering the median spectral acceleration as a measure, occurred 1.84 and 2.64 greater than the design one, and this might be an indication that the performance-based concept should be applied for pipe rack systems to achieve a safe, risk-consistent among structural and nonstructural members and cost-effective design.