Design value estimate of the residuals of the seismic response parameters of RC frames

In the evaluation of the damage levels of reinforced concrete frames both the maximum values of the seismic response parameters and the residuals values are considered. The European seismic code (Eurocode 8) prescribes to calculate the design values of the seismic response of a structure with a nonlinear behavior as the mean value of the response to at least seven accelerograms or as the maximum value of the response to at least three accelerograms. The non-exceedance probabilities of the so calculated design values are very different, are not controllable and can depend on the number of accelerograms used in the analysis. In the present study a previously proposed probabilistic method is extended, with the appropriate modifications, to the definition of conservative design values of the residuals of the seismic response parameters of reinforced concrete frames. These values, characterized by predefined non-exceedance probabilities, are calculated using a limited number of generated accelerograms. The method utilizes a value of the response estimate modified with an amplification factor defined as a function of the scattering of the response and of the predefined non-exceedance probability. In the case of values of the response parameters, as the residuals, characterized by different scatterings the proposed methodology allows to obtain homogeneous non-excedance probability levels. The proposed method is used to evaluate the residuals of the response parameters of a reinforced concrete plane frame designed according to the Eurocodes. The results, compared with those obtained applying the Eurocode 8 recommendations, show the effectiveness of the method