According to the contribution of high vibration modes to the displacement of structures

a lateral load pattern method based on multi-modes was proposed in static pushover analysis on vertically irregular structures.The accuracy of the proposed method was verified by comparatively analyzing the results of static pushover analysis and dynamic time-history analysis.In order to evaluate the influence of the degree of stiffness and strength irregularity on the nonlinear behavior and failure modes of composite frames

six vertically irregular composite frame structures were prepared by changing the strength and stiffness of the pre-existing RC（Reinforced Concrete）frames.Inter-story capacity factors of composite frame structures were calculated to quantify the stiffness and strength irregularity along the frame height

and consequently predict the weak story and the failure mode of the structures.The formation of plastic hinges and the distribution of story drift ratios were obtained from the static pushover analyses with the proposed lateral load pattern method.Results indicate that the degree of stiffness and strength irregularity directly affects the nonlinear behavior and failure mode of composite frame structures.A more uniform distribution of story capacity factor can avoid obvious weak stories in the structure

and give a more reasonable structural failure mode.