As nonlinear response history analysis (NLRHA) becomes a frequently used procedure for the seismic demand evaluation of multistory buildings, it becomes increasingly important to develop a ground motion scaling method which properly includes the dominating modes in the seismic demand estimates. This paper proposes a multimode ground motion scaling (MMS) method, which applies the square root of the sum of the squares (SRSS) or complete quadratic combination (CQC) rule in computing peak seismic demands. The aim is to minimize the weighted sum of the square differences between the spectral responses of a given ground motion and the design response spectrum for the first few modes. Using four case studies, this paper compares the effectiveness of the MMS method with the other common scaling procedures. It is illustrated that the MMS method is effective in reducing the scatter in the peak seismic demands computed from both the response spectral analysis (RSA) and the NLRHA. Recommendations for selecting the ground motion records for the application of MMS method are also provided.

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