The Effect of Torsional Ground Motion on Structural Response: Code Recommendation for Accidental Eccentricity

Abstract

In this article, data were collected from the Chiba dense array, which consists of 44 accelerometers with interstation spacing in the range of 5-300 m that are employed to estimate the torsional ground motion. The geodetic method was used to estimate torsional motions from the translational records in the Chiba dense array. The translational and computed torsional motions were then applied to the building models with different structural characteristics to evaluate the effectiveness of the accidental eccentricity levels proposed in various design codes. The results of analy- sis suggest that the 5% accidental eccentricity is on the safe side for most periods of interest in engineering practice. However, in the case of stiff structures (with periods shorter than 0.3 sec), an increase of up to four times in building displacement is ob- served by including the torsional excitation. Furthermore, we found that the acciden- tal eccentricity coefficient increased up to 0.6 at periods shorter than 0.3 sec, which is 12 times larger than what is proposed by the codes.