Abstract | The present contribution addresses the prediction of the record-to-record dispersion of peak floor acceleration (PFA) demands on elastic spatial structures. The distribution of PFA demands is approximated by an extended Complete-Quadratic-Combination (CQC) modal combination rule, based on a dispersion pseudo-acceleration response spectrum rather than the common median pseudo-acceleration response spectrum. Therefore, the selected ground motions must comply not only with target mean and but also with target dispersion spectral accelerations. Application on elastic spatial steel benchmark structures shows that the proposed methodology yields cumulative distribution functions of the PFA demand that approximate well the corresponding cumulative distributions derived in computationally expensive response history analyses.