Many researchers have studied the natural torsion of buildings subjected to earthquake ground motions, but only a few of them studied the accidental torsion. The increase in response in the flexible and the stiff edges of the building due to accidental torsion is investigated in this study, using both static and time history analyses. The accidental torsion is introduced by the accidental eccentricity provided in the Moroccan seismic code: RPS2000 version 2011. Based on the results of the time history analyses, a new practical method is proposed to assess the maximum increase in response due to accidental torsion. This method is generalized to a certain category of multi-storey buildings and presents the main advantage to avoid performing many extra seismic analyses as required in the current method of the Moroccan seismic code. The new proposed method is limited to the elastic domain to be compliant with the design procedure of the Moroccan seismic code. Further studies have to be performed to assess the efficiency of the elastic seismic design procedure that guaranties that the building will reach the required seismic level of performance by inelastic deformations.
Keywords: Accidental torsion, eccentricity, frequency ratio, earthquake, Morocco.