Characterizing the Rotational Components of Earthquake Ground Motion

Keywords: Ground motion.  Torsion.  Rotational excitations.  Seismic designs.  Surface distribution method (SDM).  Seismic arrays.  Eccentricity.  Single station procedure (SSP).  Multiple station procedures (MSP).  Seismic performance.

Abstract: The characterization of rotational components of ground motion is a focus of this report.  Two categories of procedures are derived to extract rotational components of ground motion from recorded translational data: Single Station Procedure (SSP) and Multiple Station Procedure (MSP).  The Surface Distribution Method (SDM) enables the development of a design procedure for dense seismic arrays, whose primary purpose is to extract rotational ground motions.  Design criteria are proposed to determine the length of the array, the number of recording stations and their spatial distribution.  An improved definition of accidental eccentricity is proposed and studied for a wide range of one-story elastic systems and nonlinear isolation systems.  A preliminary investigation of the effect of rotational ground motions on the response of structures is performed.  The rotational excitations are calculated using the SDM.  The sample structures are a chimney subjected to horizontal and rocking ground motions, and four-story, base-isolated and fixed-based buildings subjected to horizontal, torsional, and rocking ground motions.  Rotational components of ground motion significantly affect the response of these structures.