The Variability of Deformation Demand with Ground Motion Intensity

The use of Nonlinear Dynamic Analyses is coupled to the estimates of demands produced by earthquakes of different intensities. The uncertainties associated with these estimates are highly dependent on the variable adopted as the intensity measure. This generates the need to compare different intensity measures (IMs) and in particular the dispersion of the demand measure in relation to each IM. For this purpose correlations between maximum inter-story drift demand of nine reinforced concrete Multiple Degree of Freedom (MDOF) tridimensional structures and a number of widely used ground motion intensity parameters (GMI’s) have been investigated. GMI’s are obtained from two different sets of un-scaled ground motions, one for the Ultimate Limit State (ULS) and one for the Damage Limit State (DLS). In order to determine the optimum value of a parameter to be used as an IM, two additional non-conventional intensity parameters are analyzed, the spectral acceleration corresponding to the cracked and non-linear period of each structure, Sa(Tcrack) and Sa(T*), respectively. The results showed that these two intensity measures have the best correlation with the deformation demand. This implies that when these two parameters are used the variability of structural response tends to be lower.