A MODAL CONDITIONAL MEAN TARGET SPECTRUM METHOD TO CONSIDER HIGHER MODE EFFECT

The traditional method uses conditional mean spectrum as the target spectrum to select ground motion, which fails to effectively take into account the influence of high mode vibration of the structure. To overcome this shortcoming, a modal conditional mean spectrum method considering the influence of higher mode effect is proposed. With the weight coefficients of mode participation mass ratios, the proposed method combines the conditional mean spectrum of each mode to obtain a new target spectrum, and is called the modal conditional mean spectrum. A 30-story steel frame-center support structure was designed, and the mean conditional spectrum of interested period, modal mean conditional spectrum and uniform hazard spectrum were generated, and then 11 ground motions were selected for structural dynamic time history analysis with the 3 target spectra respectively. The results show that the structural response obtained by the modal conditional mean spectrum method considers the influence of higher mode effect of the structure, and generates obviously greater result than the traditional conditional mean spectrum. It is suggested that the proposed method be extended to high-rise structures as target spectrum.