Frequency Domain Spectral Analysis Research Articles

A simplified response spectrum method for random vibration analysis of flexible base buildings

An approximate method for determining the response of flexible base buildings is presented for random seismic excitation (single component) acting parallel to one of the principal directions of the building. The earthquake is assumed to be a wide band, stationary Gaussian process which is represented by a displacement/acceleration mean response spectrum. The building is modelled as a three-dimensional discrete lumped mass model with three dynamic degrees of freedom defined at each storey level. Five base degrees of freedom, namely two horizontal translations and three rotations, are used to represent the base flexibility. The method is developed based on the principles of random vibration analysis and uses the spectral approach to arrive at expressions for the mean peak response of the system in terms of its undamped natural frequencies, mode shapes, modal damping ratios and ordinates of mean response spectrum. The modal damping ratios are determined in an approximate manner using an energy approach. The validity of the method is checked by rigorous time domain analysis with simulated earthquake records. In addition, the results of the frequency domain spectral analysis with the power spectral density function of the earthquake process (derived from the mean response spectrum) as input are compared with those obtained by the proposed method.