Ground Motion Models for Inelastic Spectra Using NGA-West2 Database

This paper summarizes ground motion models (GMMs) developed for the inelastic response spectra of shallow crustal events. The GMMs are developed based on a large database of recordings in the NGA-West2 database with magnitude between 3.3 and 7.9, and source-to-site distances less than 80 km. GMMs are developed for six displacement-ductility levels, two damping values, and two hysteretic behavior models. One of this work’s main novelties is that the model is developed for RotD50 inelastic response instead of geometric mean, making the results directly comparable to the models developed in the NGA-West2 project for the response of elastic oscillator. The ground motion model incorporates the effect of magnitude, focal mechanism, source to site distance, site characteristic, and basin effect on the inelastic response of structures. The model shows that the yield strength demand decreases significantly when ductility goes from 1 to 1.5 (moderate nonlinearity is allowed); however, the decrease is not as significant for higher ductility levels (3 or 4). This study also quantifies the range of applicability of the “constant displacement rule.” The effect of response nonlinearity on the aleatory variability of ground motions is also quantified.