Displacement damping modification factors for pulse-like and ordinary records

In seismic codes, elastic response spectra are usually defined by assuming a conventional value for the critical damping ratio equal to 5%. damping modification factors (DMFs), i.e. scaling factors, are then applied to account for the effect of damping values higher or lower than the nominal 5%. Usually, code-mandated DMFs depend neither on ground motion characteristics nor on structural properties. However, the influence of such factors on the DMF was highlighted by different studies. In this paper, records from 110 near-fault pulse-like ground motions and 224 ordinary ground motions are used to calculate elastic displacements and DMF spectra corresponding to different values of the damping ratio ranging from 2% to 50%. The effect on DMFs of pulse period of the ground motion, earthquake magnitude, site-to-source distance, and period of vibration of the structure is discussed. By rotating the pulse-like records according to different directions with respect to the fault, including the fault-normal and the fault-parallel one, the influence of the angle of rotation is also investigated. Based on results of regression analyses, equations for the prediction of the DMF for near-fault pulse-like ground motions are finally proposed. © 2014 Elsevier Ltd. All rights reserved.