DEVELOPMENT OF AN IMPROVED INTENSITY MEASURE IN ORDER TO REDUCE THE VARIABILITY IN SEISMIC DEMANDS UNDER NEAR-FAULT GROUND MOTIONS

Intensity measure (IM) which describes the strength of an earthquake record plays an important role in the seismic performance assessment of structures. An improved IM that can reduce the variability in seismic demands helps reducing the number of records necessary to predict the seismic performance with sufficient accuracy. In this study, an improved RMS-based IM is developed based on the results obtained from incremental dynamic analyses of short-to relatively long-period frames under an ensemble of near-fault pulse-like earthquake records. It is observed that the root-mean-square value of pseudo spectral accelerations, (S-a)(rms), is generally superior to that of spectral velocities, (S-v)(rms), in seismic demand prediction under near-fault records. To compute (S-a)(rms) as IM, two appropriate period ranges are suggested for short-and moderated-to relatively long-period frames, respectively. Comparing the efficiency of (S-a)(rms) with several advanced IMs shows that (S-a)(rms) is more efficient in predicting the inelastic response and collapse capacity of short-period frames. It is also found that intensity measure (S-a)(rms) is sufficient with respect to the magnitude and source-to-site distance for all frames of various heights under near-fault ground motions.