Experimental evaluation of the nonlinear seismic response of a nuclear piping system with different support conditions

Abstract

Nonlinear analysis of nuclear power plant piping systems can be costly, and results can be questionable. However, reserve plastic ductility, evidenced in nonlinear effects, shows high reserve strength and is a very important consideration in design. Efforts are being made within the industry to benchmark analysis and observe nonlinear effects through testing. A series of tests performed on a piping system model subject to high-level seismic excitation produced much data useful to nonlinear analysis and plastic design techniques. The piping system was thin-wall stainless steel, subjected to a static pressure of 45 bar. Very high strains (in excess of 3 times yield) were observed with no catastrophic failure, contrary to what simple elastic analysis would predict. The pipe was subjected to biaxial independent motion in each of two planes. Several different spring hanger support configurations were tested, and many seismic events were run. Also tested was the effect of a visco-elastic damper used to reduce seismic effects on piping systems. The damper was found to increase damping up to 50% critical. Comparisons were made between damper, free, and rigid rod supports to observe changes in seismic stresses. The damper reduced stresses by up to 50%.