Effects of Damping Uncertainties on Damping Reduction Factors

It is apparent that the dynamic response of a building dependson its energy dissipation capacity, hence damping ratio. Thedamping value experienced by a building during an earthquakediffers significantly from the value specified in the design step.This introduces uncertainties in the design process of the building.It would be desirable to consider not only the effects ofuncertainties in loading but also the uncertainties in the structuralparameters. In this paper, the effects of uncertainties in the estimation ofdamping ratio ξ, on the use of Damping Reduction Factors (DRF) for the evaluation of high damping response spectra,are examined. Damping uncertainties are described by a lognormalprobability distribution, and the Monte Carlo techniqueis used to generate the random values of damping. Theaverage of the distribution is the deterministic value of damping (taken equal to 5%, 7.5%, 10%, 20%, 30% and 40%) whilethree different values of coefficient of variation are considered (i.e. 10%, 20% and 40%, respectively). All the DRF formulations found in the literature are not able totake into consideration damping uncertainties, leading to significantdiscrepancies in the high damping response spectra. Based on the results of this study, a new DRF formulation, ableto account for uncertainties in damping estimation, is tentatively proposed.