The Effect of the Earthquake Incidence Angle on Seismic Demand of Reinforced Concrete Structures

Because of the uncertainty of the location of the epicenter of the next earthquake, the ground motion records should be applied at any direction relative to the structure which needs to be analyzed. The structural demand produced by Non-Linear Time-History Analyses (NLTHA) varies in function of the incidence angle of the seismic input. This study evaluates the seismic directionality effects by subjecting four three-dimensional reinforced concrete structures to different scaled and un-scaled bi-directional ground motion records oriented along nine incidence angles, whose values are between 0 and 180 degrees, with an increment of 22.5 degrees. The NLTHA performed applying the ground motions along the principal axes underestimate the structural demand prediction, especially when plan-irregular structures are analyzed. The ground motion records generate the highest demand when applied in the most flexible structural direction and a high energy content of the records increases the structural demand corresponding to this direction.