Hamidreza Mahmoodi Kordkheili - Department of Civil Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr, Iran.
Alireza Zohari - Department of Civil Engineering, North Tehran Branch, Islamic Azad University, Tehran, Iran.

Irregularity of structures is one of the most important factors and reasons for the vulnerability of structures against lateral forces such as earthquakes. Building irregularities significantly affect the behavior of structural components, produce an attractive background, and intensify the forces applied. Therefore, this study investigated the response of three steel frame specimens with buckling-restrained braces (BRBs) in the ۳-, ۸-, and ۱۲-storey buildings with a span of ۵ m. The nonlinear dynamic time history analysis was performed using three near-field seismic maps, and Perform software was used for each of the models in irregular conditions of height, taking into account the horizontal and vertical acceleration of the earthquake. Then, Excel software was employed for processing the outputs. Nonlinear behavior of irregular mass frames in the height was observed by using the results of nonlinear dynamic time history analysis. The study showed that the maximum lateral displacement of the roof had very little difference according to mass irregularity and vertical earthquake acceleration in the first and last floor, but these changes increased (۱۵%) by adding the effect of vertical earthquake acceleration, especially low-rise structures. More changes in the axial force of the columns were observed when the mass was on the last floor, and with the presence of vertical acceleration, this ratio reached up to ~۲۵% for the ۳-story frame and up to ~۷۰% for the ۱۲-story frame. Moreover, changes in vertical displacement in the middle of the beams were affected by considering mass irregularities in the last floor and vertical acceleration of the earthquake, which increased the rate of changes for frames with higher heights (۳۰%).

Buckling-restrained brace, Mass irregularity