Response and Damping of Fabricated Branch Pipe Junctions Subjected to Internal Pressure and Simulated Seismic Bending

Abstract

This paper presents some of the results obtained from fifteen tests performed to investigate the ratcheting behavior of fabricated piping branch junctions subjected to steady internal pressure and dynamic resonant run pipe in-plane bending imposed to simulate seismic events. The experimental evidence confirms that the dynamic stresses are self-limiting, and thus secondary in nature. The logarithmic decrement method is used to estimate the percentage damping ratios from the steadily decaying free vibration data at the end of a forcing event. It is demonstrated that the percentage damping, measured after the component had experienced cyclic strain ranges as high as 1 percent, is rather low (1–2 percent of critical). These results are contrasted with those from the general literature, and ASME III recommended values from which it is shown that the use of higher damping ratios for similar components and loadings may underestimate the actual dynamic responses.