In this report, a direct estimation method is proposed for non-linear floor response spectrum in RC buildings with a degrading hysteretic loop based on the Takeda model. The method uses the concept of linear modal analysis with empirical coefficients and formulas characterized for the RC buildings. A shift of the resonance region, which is negligible for S buildings with bi-linear hysteresis, is also empirically evaluated for the first mode. Amplification factors of floor responses for the multi story RC buildings are verified by compared with those by nonlinear time history response analyses using number of earthquake input motions.
