On the design of piping in non linear conditions under dynamic loads

Usually the analysis of piping under the action of dynamic loads is performed making reference to elastic procedures, and allowing only a very limited energy dissipation under the form of damping (generally only a few percent of the critical value). However such limited values of energy dissipation are appropriate only if one accounts for such effects as friction, bumps etc., if the system experiences even limited amount of yielding then the equivalent energy dissipation acccunts for much larger equivalent damping values. Experimental works /1,2/ and analytical evaluation /3/ confirm the validity of this assumption; typically damping values larger than 20% are encountered with strain values just beyond yielding. Besides Lazzeri and Scala /3/ have shown that even in normal conditions, let alone emergency or faulted (in ASME meaning) conditions, yielding occurs and that it accounts for more than large damping coefficients.