A statistical study of inelastic displacement ratio spectrum for existing structures

Abstract

AbstractDisplacement‐based design has gained importance due to the emergence of the performance‐based engineering, and it has now become desirable to estimate maximum (inelastic) displacements of structures for different levels of seismic hazard. Being closely related to damage, displacement (or drift) has become an important parameter necessary to meet various performance goals. It is considered convenient to estimate the inelastic displacement demand in a structure by multiplying the elastic displacement demand of the structure with a ratio called the inelastic displacement ratio. A comprehensive study is conducted for the parametric dependence of the inelastic displacement ratio in single‐degree‐of‐freedom (SDOF) systems with known relative lateral strengths, on strong motion duration, earthquake magnitude, epicentral distance, and geological site conditions. This study is different from the earlier studies of similar types in that other governing parameters are kept fixed while the effects of variations in any particular parameter are studied. This study is based on the generation of ensembles of synthetic accelerograms from a database of 1274 accelerograms recorded in western USA for the pseudospectral acceleration (PSA) spectra of given source and site parameters. It is found that strong motion duration may influence the inelastic displacement ratios, depending on the hysteretic properties of the oscillator, in the case of durations not much longer than 10 s. Earthquake magnitude has a significant influence on these ratios for the SDOF systems of most periods, while site geology appears to be important for the stiff oscillators. A scaling model is also proposed in this study for estimating the inelastic displacement ratio spectrum from a normalized relative velocity spectrum of the ground motion. The proposed model indirectly includes the effects of various governing parameters and is shown to preserve the trends available from the direct study.