Normalization and scaling accelerograms for nonlinear structural analysis

Abstract

The paper makes a case for the legitimacy and the benefits of scalingstrong ground motion records and investigates how best to do it.In order to study scaling, comparison is made between the statisticsof ductility and normalized hysteresis energy (NHE) results for differentSDOF and MDOF structures from two sets of 20 recorded ground-motionswhere each set is chosen from a specific magnitude and distance "bin"."Normalization," defined as scaling of records within a bin to thebin median "intensity" level is examined and several different alternativenormalization parameters or "intensity" measures, e.g, normalizationto the PGA level, normalization to spectral acceleration at the structure'slowest frequency and different damping levels, frequency-averagednormalization, etc. are compared. Uncritical use of PGA is discouragedespecially for low frequency building structures while the normalizationto the spectral acceleration at the lowest natural frequency of thestructure and at higher damping (typically 5%-20%) is most convenientfor practical use and best among the alternatives. The primary advantageof normalization is that it reduces the variance of damage estimationwithout causing bias, therefore permitting the use of fewer records.