The recent rise in large-scale earthquakes has highlighted the urgent need to ensure the seismic safety of buildings and industrial facilities. A key focus in this area is the seismic performance of fire protection piping systems, which are crucial for protecting lives and property during fires. This study conducts a static analysis of three common types of piping connections—Grooved Coupling, Welding Joint, and Thread Joint—and compares their structural responses under seismic loading conditions. Notably, the nonlinear behavior of the Grooved Coupling cannot be accurately captured by a typical linear model. Therefore, a bi-linear moment-rotation relationship was developed and integrated into the AutoPIPE analysis model, enabling a detailed evaluation of stress concentration, displacement, and stiffness variation in the joints under seismic loads. The analysis revealed that the Welding Joint demonstrated the highest rigidity and stability, indicating superior seismic performance. While the Thread Joint offers benefits in terms of ease of construction and cost-effectiveness, it exhibited the weakest seismic resistance and necessitates structural reinforcement.
The Grooved Coupling, although capable of effectively dispersing and absorbing loads to a certain extent due to its flexibility, displayed nonlinear behavior with a sudden increase in stiffness and stress concentration once the joint gap closed and the tie-link was engaged. By systematically analyzing the seismic characteristics of each connection type, this study provides a comprehensive foundation for selecting appropriate joint methods in the seismic design of fire protection piping systems, taking into account structural stability, constructability, and economic feasibility. Additionally, it underscores the limitations of current technical data on Grooved Coupling, which primarily focus on strain or flexibility factors. The study advocates for the collection of experimental force–displacement data to enhance modeling accuracy. These findings aim to contribute to the development of more reliable seismic analysis models and design standards that reflect real external loading conditions.