Published in Department of Civil & Environmental Engineering, California Polytechnic State University, San Luis Obispo, May 30, 2002.
Four fire protection systems have been attached to a small building model for testing their dynamic properties. Three of the systems used CPVC (fire rated) plastic pipes while the fourth was made from schedule-40 steel pipe. The building model was securely attached to a three by three foot shake table in one of two orientations and was able to experience base accelerations along both its principle axis (longitudinal, transverse). Test procedures involved sending a sine sweep with a progressively increasing frequency at a constant acceleration value. Various recording locations provided data showing fundamental frequencies with pronounced amplification over the base input accelerations. First the buildings natural frequencies were obtained. Then each sprinkler system was tested for acceleration values at the sprinkler drops. Sprinkler drops were affixed with an accelerometer at the fitting connection and one at the sprinkler head. Comparisons are made between the fundamental frequencies of the building and the fire sprinkler system. An analytical model of the four sprinkler systems was designed on the SAP2000 computer program. The test frequency range providing clean data was from 10 Hz – 25 Hz. In this range the computer analysis identified all of the first observed fundamental frequencies. The SAP2000 Analysis also identified the distinct second fundamental frequencies obtained from testing. Large acceleration amplifications were observed at fundamental frequencies in the building and in the sprinkler systems. The largest amplification was sixty times that of the base input experienced by one of the CPVC drops. The steel sprinkler line also experienced large amplification values of up to 35 times the base level acceleration. The fire systems were filled with water to simulate a wet-system and to indicate potential failures. No failures occurred in any of the four test systems. After testing each sprinkler design multiple times it is concluded that sprinkler systems should remain functional following a seismic event. Sprinkler systems installed to NFPA-13 code (National Fire Protection codebook) standards have been proven to perform in earthquakes as well as the structures they’re attached to. Improper connectors and lack of required pipe clearances are the main factors attributed to researched fire system failures.
Civil and Environmental Engineering