ELSEVIER Nuclear Engineering and Design 166 (1996) 69 83 Nuclear Engineering and Design Effects of ductility on seismic response of piping systems and their implication on design and qualification Ayman M. Okeil, Chi C. Tung Center .[br Nuclear Power Plant Structures, Equipment and Piping, Box 7908, North Carolina State Unit,ersity, Raleigh, NC 27695-7908, USA Received 10 August 1995 Abstract This study is concerned with the inelastic seismic response of nuclear power plant piping systems. Two systems are examined. The first one is an idealized four-equal-span pipe run and the second one consists of two configurations modified from an existing pipe run. Detailed finite element seismic time history analyses are performed using the AnSYS computer program. By varying the various geometrical and physical parameters, calculations are made for a total of 76 cases. The results show that ductility generally contributes to reducing the response of piping systems. An empirical relation between the support load reduction factor and support ductility demand is given and a chart and simple procedures are suggested for the design and qualification of piping supports taking ductility into consideration. I. Introduction In addition to resisting operational loads, nu- clear power plant piping systems must also demonstrate structural integrity under earthquake loads. Current design practice is based on linear analysis where stresses due to design loads are calculated and compared with allowable stresses. Owing to this and many other overlapping con- servatisms, piping systems at present tend to em- ploy a large number of supports and are usually rather rigid. These rigid and overly constrained systems may experience high stresses under ther- mal and other transient loads. It has been com- monly held that if piping systems possess a certain degree of ductility and if a moderate amount of yielding is allowed, support loads due to earth- quakes may be reduced and fewer supports are needed (Mohammadi and Amin, 1987; Varadara- jan et al., 1979). Piping systems are regularly reviewed for new or modified loads which are sometimes higher than those for which the systems were originally designed to resist. Any reduction in response due to ductility will have a positive impact on the design and qualification processes. For near-term qualification, removal of conservatism inherent in the methods of analysis and design may resolve many of the problems. For long-term qualifica- tion and sound design it is important to have a thorough understanding of the inelastic behavior of piping systems. Although much effort has been spent in the last 20 years or so studying the non-linear inelastic behavior of piping systems under earthquake loads, the emphasis has been on the development of appropriate methods for 0029-5493/96/$15.00 ©' 1996 Elsevier Science S.A. All rights reserved Pll S0029-5493(96)01236-8