Effect of synchronization of vertical and horizontal ground motions on the dynamic responses of portal frames taking into account of P-delta effects

Buildings are subjected to horizontal and vertical ground motions during a seismic event. The response of the buildings to the combined effect depends on the properties of the ground motion components like intensity, frequency content and arrival time interval. In this study, the effect of synchronous horizontal and vertical ground motions on the dynamic responses of portal frames is investigated with the specific objective of correlating the fundamental horizontal period of the portal frames with the arrival time interval corresponding to their worst dynamic responses. A multiparametric study is conducted using Ricker Wavelets to represent ground accelerations. Sixten portal frames with a horizontal fundamental period from 0.25 to 4 seconds are analysed 400,000 each for the combined effect of vertical and horizontal ground motions, considering the P-delta effect. The difference among the 400,000 analyses is the value of the arrival time interval and predominant period considered. The study's results showed that for the low level of peak horizontal ground acceleration (PHGA), the worst dynamic response of a frame, except for vertical spectral acceleration and horizontal spectral velocity, occurred when the arrival time interval was about 0.9 of the horizontal period of the frame. However, for a high level of PHGA, the worst dynamic response of a frame occurs when the arrival time interval is close to zero. The other main parameter considered in the multiparametric study was the predominant period. The predominant period that corresponds to the worst dynamic responses of a frame is twice the horizontal period of the frame.