This study presents a comprehensive seismic vulnerability assessment of an urban gas distribution network under design-level earthquake scenarios. The analysis employs site-specific spectral data and frequency response spectra for the target region. Ground-surface displacements were modeled for several soil types to capture the influence of local site conditions. A three-dimensional finite-element model of the network was developed from detailed two-dimensional maps and topographic data, incorporating pipe materials, diameters, and connection configurations. A dedicated algorithm was implemented to evaluate stress-concentration factors at connection nodes, enabling accurate estimation of stress distribution throughout the system. Using random vibration theory, stress variations at nodal and joint locations were quantified, providing insight into the dynamic response of the system under seismic loading. The Naysar gas network in Sanandaj, Iran, served as the case study. The results indicate that the most severe damage occurs in 6-inch steel pipelines located in soil sites during earthquakes with return periods of 475 and 2475 years. In rock sites, the highest vulnerability is likewise associated with 6-inch steel pipes, though primarily under the 2475-year event. In contrast, polyethylene (PE) pipelines remain largely stable at all hazard levels, with fewer than 5 % of nodes exceeding their allowable deformation limits. Results highlight that network vulnerability depends strongly on soil type, pipeline material, and geometric configuration. The highest stresses occur at connection points, identifying them as the most critical elements. The findings demonstrate the importance of adopting site-specific design measures and advanced analytical approaches to enhance the seismic resilience of urban gas networks.
