Limit state assessment for bending deformation of multi-ply bellows systems

Abstract

Applying seismic separation joints to increase the piping deformation capacity is an efficient way to improve the seismic performance of piping. Bellows have the flexibility and low stiffness, enabling an effective response to large deformations. They can be applied as seismic separation joints in piping. This study applied the cyclic bending load to evaluate the seismic performance and assess the limit state for the bending deformation of bellows systems. Experiments were conducted using two series of multi-ply bellows systems to determine the difference in performance with respect to the number of plies. The leakage caused by fatigue cracks in the bellows systems was analyzed to consider the low-cycle fatigue crack due to seismic loads. The bellows systems were filled with water for conditions used in the field, while internal pressure was maintained during the experiments. The seismic performance of bellows systems for bending deformation was evaluated using cyclic loading protocols that referenced FM-1950 and FEMA-461. The experiments were performed by applying cyclic loading for the constant amplitude to assess the limit state for bending deformation of the bellows systems with respect to displacements evaluated using the two cyclic loading protocols.