A simplified formulation is presented for determining the maximum horizontal acceleration response of rigid floors in multistory structures subjected to strong ground motions. The proposed formulation may be easily incorporated into the framework of modern seismic design provisions for the design of nonstructural components. The method takes into account the nonlinearity of the primary structure. Floor acceleration data obtained from 74 earthquake simulations performed on 30 small-scale multistory reinforced concrete test structures are used to develop the proposed formulation for floor acceleration maxima. The simulations considered were limited to roof displacements between 0.5% and 2.5% of the structure height, where the test structures experienced extensive cracking and flexural yielding without losing structural integrity. This level of deformation is within the range of response expected in full-scale multistory buildings during strong seismic events. For the simulations considered, the mean for the ratios of measured-tocalculated floor accelerations is 0.85 with a coefficient of variation of 0.30, of sufficient accuracy considering the simplicity involved in the calculation and the uncertainty associated with earthquake ground motions. The results are consistent for various structural types and for a wide range of base motions.