Accidental eccentricity in symmetric buildings due to wave passage effects arising from near-fault pulse-like ground motions

Abstract : This article investigates the characteristics of the accidental eccentricity in symmetric buildings due to torsional response arising from wave passage effects in the near-fault region. The soil-foundation-structure system is modeled as a symmetric cylinder placed on a rigid circular foundation supported on an elastic halfspace and subjected to obliquely incident plane SH waves simulating the action of near-fault pulse-like ground motions. The translational response is computed assuming that the superstructure behaves as a shear beam under the action of translational and rocking base excitations, whereas the torsional response is calculated using the mathematical formulation proposed in a previous study. A broad range of properties of the soil-foundation-structure system and ground motion input are considered in the analysis, thus facilitating a detailed parametric investigation of the structural response. It is demonstrated that the normalized accidental eccentricity is most sensitive to the pulse period (T-P) of the near-fault ground motions and to the uncoupled torsional-to-translational fundamental frequency ratio (Omega) of the structure. Furthermore, the normalized accidental eccentricities due to simplified pulse-like and broadband ground motions in the near-fault region are computed and compared against each other. The results show that the normalized accidental eccentricity due to the broadband ground motion is well approximated by the simplified pulse for longer period buildings, while it is underestimated for shorter period buildings. For symmetric buildings with values of Omega commonly used in design practice, the normalized accidental eccentricity due to wave passage effects is less than the typical code-prescribed value of 5%, except for buildings with very large foundation radius.