A Reduced‐Order Model for Performance‐Based Seismic Design of Suspended Piping Systems in Buildings

Among non‐structural elements, suspended piping systems are critical to building functionality, enabling water circulation, waste disposal and fire suppression. Their seismic damage can lead to prolonged downtime, internal flooding and substantial direct and indirect economic losses. Yet existing approaches for assessing their seismic performance are either judgement‐based or computationally intensive, making them unsuitable for conceptual design, where multiple configurations must be rapidly explored. This paper introduces a reduced‐order model that enables efficient derivation of seismic fragility functions for suspended piping systems that have a known, regular restraint layout with quality‐controlled installation. Motivated by qualitative observations from a three‐degree‐of‐freedom suspended piping subassembly, the method adapts an equivalent linear static procedure originally developed for estimating the transverse displaced shape of pier‐supported bridges. The approach requires condensing each longitudinally excited pipeline into a single mass–spring system and applying a simplified force‐distribution rule at orthogonal connections. Once the displaced shape is obtained, the system is transformed into an equivalent single‐degree‐of‐freedom representation. The model is benchmarked against nonlinear time‐history analyses of nine suspended piping archetypes using full three‐dimensional multi‐degree‐of‐freedom models. Results show that peak displacement estimates at the critical support fall within a 10% relative error band for 73% of cases and within 20% for 92% of the archetype‐direction‐intensity cases investigated. A fragility analysis for one archetype shows that the medians of the resulting fragility functions differ from those of the full model by less than 10%, illustrating how the model supports rapid, mechanics‐based performance‐based design of engineered systems with regularly spaced seismic restraints.