The uncertainty in the seismic demand of a structure, corresponding to uncertainties in ground motion and in structural properties, needs to be properly characterized in reliability analysis. In this study, the sensitivity of structural response to major uncertain variables is investigated using the variance-based method in order to determine which variables are most significant. The Sobol' decomposition, based on a Monte Carlo simulation, is used to decompose the variance of the response into contributions from the individual ground motion and structural properties as input variables. The formulation of dynamic structural response using random vibration theory, based only on the frequency information of the excitation, can provide an important basis for analytical sensitivity analysis of structural response. The results show that the uncertainties in ground motion are more significant than uncertainties in structural properties for global structural response, especially peak roof displacement and maximum inter-storey drift.
