A modified CCFS approach for the seismic analysis of multiply supported MDOF secondary systems

An alternative technique has been developed to evaluate the ordinates of the Cross Cross Floor Spectra (CCFS). The technique properly accounts for the dynamic interaction, tuning and non-classical damping characters of the combined Primary-Secondary (P-S) systems. The approach is able to estimate the peak response of the tuned non-classically damped P-S systems more accurately. In the analysis, two fictitious oscillators are attached to the primary system in the course of evaluating the ordinates rather than attaching only one oscillator to the primary system as was previously suggested. Two numerical examples are analyzed by the original and the proposed techniques. The results are compared with the response values obtained using coupled dynamic analysis. The proposed technique proved to be more accurate in estimating the peak response of the secondary system, specially in cases of tuned, non-classically damped P-S systems.