Analysis of Natural Frequency Characteristics and Resonance Risk of Sprinkler Piping Systems

This study evaluates the seismic performance of fire protection piping systems from a dynamic perspective by conducting modal analyses of horizontal branch lines and vertical risers. Using Bentley AutoPIPE, piping models were developed to estimate natural frequencies and mass participation factors. For horizontal branch lines, cumulative mass participation exceeded 80% across all modes, confirming the reliability of the analysis. A fundamental frequency of 1.48 Hz was observed in the lower modes, overlapping with the low-frequency range (0.1∼5 Hz) of domestic earthquake ground motions, indicating a significant risk of resonance. For vertical risers, the fundamental frequencies ranged between 10 and 18 Hz depending on pipe height and diameter. In particular, for 100 A risers, the frequency fell below 13 Hz, approaching the predominant frequency (13 Hz) recorded at the KMA05 seismic station, suggesting potential resonance. These findings demonstrate that conventional static analysis–based seismic design is inadequate for assessing resonance risk, highlighting the necessity of dynamic analysis–based evaluations of seismic performance.