Rotational Components of the Ground Motion for Vrancea Earthquakes

The ground motion during an earthquake includes translational and rotational components. The rotational component about a vertical axis generates torsional effects even in symmetrical buildings. The angular acceleration time histories are obtained from the translational acceleration on three orthogonal directions, recorded during 1977 and 1986 Vrancea earthquakes for different site conditions. The torsional response spectra for these sites and the average normalized torsional spectrum for Bucharest are computed. The influence of the ground motion rotational component on the elastic seismic response is analysed for symmetrical and for non-symmetrical systems. The study is made on systems with different eccentricities and stiffnesses, considering simultaneously the recorded translational components and the computed rotational component of the earthquake ground motion.