Comparison among different scaling methods for earthquake records used for seismic nonlinear analysis of structures

Current Italian and European seismic codes allow evaluating the dynamic nonlinear behaviour of structures using time-history analysis. In this case one of the main issues to be solved is the selection of the accelerograms according to the code prescriptions. The choice of seismic input should be addressed with natural records: in this way it is possible to represent the earthquake with its main characteristics i.e. its amplitude, frequency and energy content, duration and phase. If natural accelerograms are adopted, the above mentioned prescriptions strongly condition the search for the "best" seismic input and they often require the real accelerograms to be altered by scaling techniques. In the current paper, the influence of different scaling methods is evaluated. Seven methods of scaling are taken into account and the variation coefficients (CoV), calculated in terms of spectral ordinates for sets of elastic and inelastic spectra, are evaluated and compared. It is concluded that if the CoV of the structural response must be contained, it is convenient to refer to scaling procedures that explicitly consider the fundamental period of the structure e.g. Kappos intensity and Matsumura intensity.