Using spectrum-compatible ground motions for deriving damping modification factors

Damping modification factor (DMF) is utilized in seismic design codes for computing high damping response spectra from their 5%-damped counterpart. These high damped response spectra are used for designing buildings with base isolation and supplemental damping devices. The current research aims at investigating DMFs derived from spectrum-compatible ground motions. Two ground motion datasets were selected and scaled from the PEER database using the two types of spectra in the current Egyptian code as target spectra. DMFs were derived using the two ground motion datasets and represented by empirical equation with suitable coefficients for each dataset. The resulting DMFs were compared to Eurocode 8 (EC8) expression and previous studies. The mean exact DMFs for dataset (1) at periods between 1.5 and 3 s had very good agreement with EC8. For dataset (1) and at damping ratio of 10%, the empirical equation had excellent matching with previous expression derived from moderate earthquakes in Egypt. The results of this study have also assured that by decrease in magnitude of earthquake, the resulting values of DMF exhibit higher tendency to approach unity at longer periods. The approach of using spectrum-compatible ground motions to derive DMFs showed a reasonable efficiency and may be useful if local strong motion records are scarce.