A simplified algorithm for evaluating the Seismic Return Period of Structural Capacity

The modern technical rules define the proper seismic evaluation on the basis of reference period (reference life), established according to importance and use of the building. At the reference life is associated, to the different limit states, a return period for the seismic action. In Italy, seismic hazard maps were adopted, which by means of the geographical coordinates of the site allow to assess (for specific return periods) the elastic spectral shape, which defines the reference seismic action. Until now, the non-linear static methods, as the N2 method, allow to assess the seismic demand in terms of displacement starting precisely from the spectral shapes. However, it is difficult to quantify the seismic return period associated with the real strain capacity of the structure. In this paper is presented an algorithm based on the reverse application of the N2 method. The algorithm allows the assessment of the return period representing the seismic capacity of the structure (expressed in years), starting from the capacity curve of equivalent system. The capacity curve is defined once known the elastic stiffness, the yield and ultimate displacement at the limit state considered. The procedure is validated by comparison with the results of pushover analysis relating to an existing RC building obtained by locating it, respectively, in area at low, medium and high seismicity.