Spectral matching RotD100: Effects on bidirectional lateral demand of reinforced concrete frame buildings

Abstract

Different approaches are used to generate ground motion sets compatible with a target RotD100 spectrum following current ASCE7 requirements. The sets are used as input to perform bidirectional nonlinear response history analyses and evaluate the imposed deformation and energy demands. The structures studied are multistory buildings comprised of space frames designed to resist both gravity and earthquake forces. The influence of reinforcement detailing is explored by varying the ratios between the nominal moment capacities of beams and columns. A wide range of inelastic demands is investigated by scaling the intensity of the input motions. It was found that the marked disparities between the demands exhibited by the various sets can be explained by the differences in the spectral amplitudes along the expected periods of vibration. The traditional approach of spectral matching each horizontal component separately to the target RotD100 spectrum generates records with disproportionate intensities causing unrealistic large inelastic demands when compared to the results expected from amplitude-scaled records. On the other hand, the sets generated by simultaneous modification of the horizontal components to directly match the target RotD100 spectrum exhibited the tightest match to the target and the closest ground motion characteristics (Arias Intensity, significant duration, directionality, and spectral dispersion) to the amplitude-scaled sets. These sets also imposed the mean peak drift and mean total energy demands closest to the imposed by the amplitude-scale sets; however, the mean peak drift demand was slightly but consistently below the expected from amplitude-scaled sets. This unconservative bias vanished when the same approach was implemented using 110% the target spectrum to comply with the ASCE7 minimum spectral amplitude requirement for spectrally matched records.