Enhanced seismic criteria for piping

摘要

In situ, or laboratory, experience have shown that piping systems exhibit a very satisfactory seismic behavior.rnSeismic motion do not achieve to significantly damage piping systems unless large differential motions of anchorage arernimposed. Nevertheless, present design criteria for piping are very severe and lead to require a large number of supports, whichrnoverly rigidify the piping systems. CEA, in collaboration with EDF and FRAMATOME, are working on proposals forrnenhanced design methods, less severe, but still conservative, and compatible with defect justification during operation.rnOur approach is based on the difference between the real behavior (or the computed one) with the codified methods.rnCriteria are applied on an elastically calculated behavior that can be significantly different from the real one : the effect ofrnplasticity may be very meaningful, even with low incursion in the plastic domain. Moreover, and particularly in pipingrnsystems, the elastic follow-up effect affects stress distribution, for both seismic and thermal loads.rnFor seismic load, we have proposed to modify elastic moment limitation, based on the interpretation of experimentalrnresults on piping systems. The methods have been validated on more industrial cases, and some of the consequences of thernchanges have been studied : modification of the drawings and of the number of supports, global displacements, efforts in thernsupports, stability of potential defects...rnThe basic aim of the studies undertaken is to make a decision on the stress classification problem, that is not limitedrnto seismic induced stresses and to propose simplified method to cope with.