Influence of scaling of different types of ground motions on analysis of code-compliant four-story reinforced concrete buildings isolated with elastomeric bearings

Understanding the effects of selection and scaling of ground motions on the response of base-isolated buildings is important because these structures are routinely designed using nonlinear response history analysis (RHA). Previous studies lack a comprehensive evaluation of the influence of choices made in the selection of type of ground motions and the method of scaling on a range of response indicators of code-compliant base-isolated reinforced concrete (RC) buildings. Therefore, in this study four-story base-isolated RC buildings with a range of isolation system properties are designed in accordance with the provisions of ASCE 7-10 and large sets of near-fault pulse-like and far-fault non-pulse-like ground motions are considered. The effects of scaling (weighted scaling versus spectral matching) on the mean values as well as dispersions of various response indicators are systematically evaluated. Uncertainties in isolator properties are accounted for by conducting bounding analysis. Three-dimensional finite element models are developed considering nonlinearity of the isolation system as well as that of the superstructure and RHAs are conducted using risk-targeted maximum considered earthquake (MCER)-level ground motions. It is found that the type of ground motion and scaling method have more pronounced effects on superstructure response indicators compared with those on isolation system displacement demands. For the base-isolated buildings considered in this study, inter-story drift ratios and column curvature ductilities are affected significantly due to the choices made in the selection and scaling of ground motions while superstructure base shear forces and roof accelerations are less severely affected. Lengthening of the fundamental period was found to be more efficient than increasing effective damping in the isolation system in order to not only reduce superstructure demands but also to reduce the variability of the superstructure response to selection and scaling of ground motions.