No abstract

No abstract

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