Displacement-based seismic analysis of underground lifelines using response surface-based strain predictions

Underground lifelines are critical infrastructure essential for economic development and daily life. Earthquake-induced damage can significantly disrupt communities and cause substantial secondary losses, with repairs often requiring considerable time and expense. Despite the importance of seismic performance assessments, Korea currently lacks well-established design standards comparable to those of the American Lifelines Alliance. As strong domestic earthquakes become more frequent, the need for reliable seismic evaluation and design of underground lifelines has become urgent. Since underground lifelines deform together with the surrounding soil during seismic events, displacement-based static analysis is more appropriate than dynamic analysis. This study estimates ground displacements using ground strains derived from wave propagation theory, accounting for the spatial distribution of seismic effects. These displacements are then translated into loads using the Winkler spring model and applied in finite element analysis. A total of 4,000 analyses were conducted to develop response surfaces using second-order polynomial regression within the response surface method framework. The resulting models enable efficient strain estimation without requiring additional detailed analyses. This approach supports the development of practical seismic assessment guidelines for high-risk areas and offers a cost-effective tool for preliminary design and safety evaluation.