Definition of a model for the damping modification factor for near-fault records

Damping modification factors (DMF) are scaling factors to be applied to the 5% damped spectral ordinates to take into account damping values higher or lower than the nominal values of 5% of critical. DMF have been already introduced in several seismic codes. Moreover, in different studies the influence of basic parameters on DMF is analysed and empirical expressions are proposed. In this context, the attention is herein focused on the effect of damping ratio on single-degree-of-freedom systems subjected to near-fault records. Specifically, 248 accelerograms recorded in near-fault regions during different earthquakes are considered; the recorded accelerograms have been rotated into fault-normal and fault-parallel components. For the parametric study seven damping ratios (from 2% to 50%) are considered to evaluate the DMF. The effect of magnitude and period of structural vibration on DMF is evaluated and a simple model, obtained from regression analyses, is proposed. The research confirms the period-dependent nature of the DMF and the influence of magnitude