Comparison of the drift spectra generated using continuous and lumped-mass beam models

The drift spectrum, as a new measure of earthquake-induced demands in structures, was developed using a uniform-stiness continuous beam model. Practical limitations in the procedures based on such models have caused structural engineers to pay little attention to drift spectra. In this paper, a method is proposed to estimate the seismic-induced inter-story drift demands, using the modal analysis technique of lumped mass, non-uniform beam models. The proposed approach is simple and can overcome many deciencies of the previous methods. It can take into account the very important eect of height-wise stiness reduction on drift demands, without the numerical diculties usually encountered in computing the drift spectra. The drift spectra for high-rise shear buildings are computed using both continuous and lumped mass beam models. The comparisons indicate that the results of the continuous uniform-stiness beam models in some cases are not acceptable. The eects of various parameters such as the structural system, the heightwise variation of structural stiness, the number of stories, higher modes and damping ratios on inter-story drift demands are investigated. Also, the in uences of the structural system and height-wise variation of structural stiness on the height-wise distribution of maximum inter-story drift demands are evaluated using a number of building models.