Seismic fragility of threaded Tee-joint connections in piping systems

This paper proposes a methodology to evaluate seismic fragility of threaded Tee-joint connections found in typical hospital piping systems. Existing experimental data on threaded Tee-joints of various sizes subjected to monotonic and cyclic loading indicates that the “First Leak” damage state is observed predominantly due to excessive flexural deformations at the Tee-joint section. The results of the monotonic and cyclic loading tests help us evaluate the characteristics for a given pipe size and material. A non-linear finite element model for the Tee-joint system is formulated and validated with the experimental results. It is shown that the Tee-joint section can be satisfactorily modeled using non-linear rotational springs. The system-level fragility of the complete piping system corresponding to the “First Leak” damage state is determined from multiple time-history analyses using a Monte-Carlo simulation accounting for uncertainties in demand.