The indices of the effects of the dynamic torsional coupling are investigated, using the simplest analytical model: a single story linear system with an uniaxial eccentricity. The main results are as follows: The formulae of the peak response under simplified input ground motions were derived in an explicit form. Based on them, the fundamental properties of the dynamic torsional coupling were investigated and two simple indices were proposed. These indices can indicate rationally the effects of the torsional coupling whether the eccentricity is large or small. For example, they cover the torsional coupling induced by the small eccentricity that is inherent in the dynamic one.
