ABSTRACT
The existence of different definitions of the uncoupled torsional to lateral frequency ratio has led to a diverse range of results as to the significance of this parameter. The theoretical basis of the four different descriptions of this parameter is clarified. For a single storey structure, the torsional stiffness and the mass polar moment of the floor area are identified as the system’s physical properties. The equation of motion is extended from its parametric linear form to include parametric nonlinearity due to stiffness softening. The effects of the phase components of two orthogonal and horizontal accelerograms are investigated. First, the effects of harmonic components of generalized seismic accelerations are discussed with reference to a parametric study. Numerical studies have shown that there is a phase difference induced resonance of the torsional mode. This work is extended to a set of real accelerograms. The phase components of these accelerograms are derived by the use of a fourier transform and the importance of phase difference information of the seismic input is discussed.
