Ground motion rotation effects on bidirectional inelastic response using seismic input compatible to a target RotD100 spectrum

Abstract

This article investigates the effect of rotating RotD100 compatible ground motion horizontal components on the inelastic demands predicted by nonlinear response history analyses. Different methodologies for the generation of the compatible records are investigated: amplitude scaling, independent spectral matching of each horizontal component and tight spectral matching to the target RotD100. Two types of reinforced concrete structures were studied, idealized single columns bridge piers and 4 storey height space frame buildings. The in-plane geometric characteristics of the models were defined to cover a wide range of azimuth dependency. It is shown that the directionality in the structural response is dominated by the azimuth dependency of the structure lateral load resisting system. While negligible for near-axisymmetric structures, response directionality rapidly increases as the structural system starts exhibiting azimuth dependency. Results obtained for individual records show that rotating the horizontal components at different angles generated maximum peak drifts 30 % larger, in average, than the average peak drift from all rotations studied. The directionality effect is reduced when considering mean results from sets of 11 records, the expected demand from a set with motions at a fixed rotation was ±10 % the expected demand when rotations were included. However, the differences between the peak drift exceedances percentages obtained from the sets and the expected percentage of exceedances when rotations are included were between ±25 % and ±35 % depending on the azimuth dependency and complexity of the structure. No correlation was found between the response directionality and the level of inelastic lateral demand, the methodology used to generate the seismic input or the directionality in the input record.