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Analytical Seismic Fragility of Fire Sprinkler Piping Systems
Civil and Environmental Engineering
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For the first time, a comprehensive simulation methodology is developed for fire sprinkler piping systems and is used to generate seismic fragility parameters of these systems. The experimental-based analytical model accounts for inelastic behavior constituents of the system including: threaded joints, grooved joints, solid braces, cable braces, hangers, and restrainers. The model incorporates a newly developed hysteresis model for threaded and grooved tee joints that is validated by the experimental results of several tee subassemblies. The modeling technique at the sub-system level is validated using the experimental results of four different piping subsystems. The methodology is used to obtain the seismic response of the fire sprinkler piping systems of University of California at San Francisco (UCSF) Hospital under two different suites of ninety-six artificially generated tri-axial floor acceleration histories. Eight classes of piping systems with variations on types of braces, weights, joints, and location of restrainers are considered in this study. After the component fragility parameters are obtained for the components of all piping cases, system level fragility parameters are defined, and a joint probabilistic seismic demand model is utilized to develop system fragility parameters. The effect of seismic performance variation on eight classes of piping systems were examined through component and system level fragility curves. These curves showed that the main run pipes with grooved type joints are more vulnerable compared to the threaded joints. Removing the water weight from the piping system reduced the failure probability in all component (specially in grooved joints). Cable braces are found to be more vulnerable compared to the solid braces. The behavior of armover pipes was improved by removing the wire restrainers from these pipes. Finally, the probability of the impact between the pipes and their surrounding contents is studied by providing different clearances from the piping system. To do so, the displacement demands on the fire sprinkler systems are studied through two sub-system level experiments and two designed classes of the UCSF piping plan. The displacement fragility curves for large and small pipe diameters are obtained and compared with the probability of damage inside piping systems. These curves showed that, by providing 3in and 8in clearance from large and small pipe diameters respectively, the leakage failure in piping systems is more probable compared to the first pounding of piping system to its surroundings.