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

Some analyses have been performed about the behaviour of non linear systems under the contemporary action of a dynamic component superimposed to a static force. The main conclusions are as follows: a) Ductility is a decisive factor in the assessment of the behaviour of an elastoplastic system under dynamic loads; the elastic analysis would predict unrealistic large peaks, which are easily smoothed away by small yieldings. b) Total ductility values (i.e. considering the whole loading cycle and hence possible ratcheting phenomena) around 7.5, 15.0 represent a conservative evaluation of the corresponding strain tolerable by the piping. c) Static coefficient, as causing ratcheting, is a decisive factor in assessing the response of the system; values in excess of 0.5-0.75 produce such a large level of yielding that very limited overcoming of the elastic limits produces very strong ratcheting, hence only limited beneficial effects are present. On the contrary if values within 0.25 are found then the beneficial effect of yielding on the amplification is substantial. (orig.)