CQC modal combination rule for high‐frequency modes

The CQC rule for modal combination is extended to include the quasi‐static contribution of truncated modes and the effects of input narrow‐bandedness and cut‐off frequency. A simple measure of the error in approximating a high‐frequency modal response by its quasi‐static contribution is derived. The extended rule is applicable to structures with high‐frequency modes and to seismic inputs which may not be regarded as wide band. Numerical examples demonstrate the significance of input bandwidth and cut‐off frequency on modal cross‐correlation coefficients, and on the error resulting from truncation of high‐freqeuncy modes.