SIMPLIFIED METHOD TO PREDICT RELATIVE MOTION BETWEEN TWO INELASTIC STRUCTURES SUBJECTED TO TIME-LAGGED BASE MOTIONS

A simplified method to estimate the peak relative displacement between two inelastic structures is proposed by considering their vibration phase and time lag of their base motions. Peak differential base displacement is obtained from the difference between displacement time histories of the two remotely located bases. Peak differential structure displacement, defined as the peak difference between displacements of inelastic structures measured from. the respective bases, is estimated by the extended spectral difference (SPD) rule and elastic response spectrum, without conducting time-history analysis of the structures. The extended rule considers inelastic vibration phase between the two structures that is affected by structural properties, ductility demands, and time lag of base motions. Thus-obtained two differential displacements are combined to estimate the peak relative displacement, and its accuracy is validated using numerous code-compatible building pairs, 33 earthquakes, and a number of presumed time lag scenarios. Using the method, reasonable time lag magnitude and its effect are discussed. The method is believed to be the most efficient among those available to-date.