2 METHODS FOR SEISMIC ANALYSIS OF NONCLASSICALLY DAMPED SYSTEMS

Two methods of seismic analysis of non-classically damped systems are compared. The first method is an extension of the Foss method (called the modified Foss method here) in which the response in the time domain is represented in terms of real modal vectors and relative displacements and velocities of the equivalent single-degree-of-freedom (SDOF) systems. In the second method, known as the canonical method, a different set of real modal vectors along with sine and cosine responses of the equivalent SDOF systems are used. It is shown that the canonical method can be derived along the same lines as the modified Foss method. The time domain responses from the two methods are identical and the corresponding response spectra responses comparable. The modified Foss method is preferred because of the physical significance of the relative displacements and velocities used in the method.