Spectrum-based response prediction of asymmetric structure with supplemental viscous damping

Seismic response of one-story structure with the significant stiffness eccentricity, developing a torsional mode, is studied in this paper. Viscous damping is added to reduce both the translational and torsional vibration of the structure. The structure in such a case possesses the so-called non-proportional damping, which makes the conventional modal analysis using undamped vibration mode more inaccurate. On the other hand, more accurate method using the complex-valued mode is not easy for practical analysis, and is not very effective to understand dynamic response characteristics of the structure. Hence, this paper proposes a new modal analysis which uses the real-valued mode and yet treats the non-proportional damping effect with a unique correction process. Many cases of non-proportional damping are examined, and the reasonable accuracy of the proposed method is demonstrated through comparison with the other existing methods.