سپيده شهريور

In this study, the seismic behavior of vertically irregular steel frames equipped with buckling‑restrained braces (BRBs) is investigated. Furthermore, the effect of seismic sequences (aftershocks) on the reduction of performance levels in these structures is eva‎luated. To this end, three steel structures with 3, 5, an‎d 10 stories, each with a plan dimension of 24×24 meters an‎d a story height of 3 meters, an‎d exhibiting geometric irregularity an‎d discontinuity in the lateral‑load‑resisting system, were designed using the performance‑based design method. The structural design was performed in SAP2000 software in accordance with relevant design codes. To assess the actual performance of the structures, nonlinear dynamic analyses were carried out in OpenSees under seven real far‑fault ground‑motion records. The analysis results indicated that the studied frames exhibit deformation concentration in the middle an‎d upper stories an‎d increased inter‑story drift deman‎d in specific levels. However, the use of BRBs transformed the lateral response of the structures from irregular to a near‑regular behavior. In the three‑story structure, displacement distribution remained uniform an‎d below the design target limit of 1.75%. In the five‑story frame, the middle stories absorbed the highest energy, while in the ten‑story frame, although initial irregularity caused deformation concentration in the upper stories, the BRBs were able to control lateral drift an‎d excessive deformations by increasing the effective stiffness. Additionally, the eva‎luation of seismic sequences showed that the occurrence of aftershocks leads to a significant increase in displacement an‎d acceleration deman‎ds in all three structures. Maximum displacement increased by approximately 13% in the three‑story structure, about 22% in the five‑story structure, an‎d around 12% in the ten‑story structure relative to the mainshock. Moreover, as the number of stories increases, the effects of aftershocks on displacement an‎d acceleration responses become more pronounced, resulting in a decrease in the structural performance level. Overall, the findings of this study indicate that the use of BRBs in irregular steel frames leads to substantial improvement in seismic performance, reduction of vertical irregularity effects, an‎d enhanced structural safety under severe earthquakes. Nevertheless, the importance of considering seismic sequence effects in the design of such structures—due to their impact on reducing performance levels—is strongly emphasized.

طراحي بر اساس عملكرد , مهاربند كمانشتاب , نامنظمي در ارتفاع , رفتار هيسترزيس , توالي لرزهاي

Performance‑based design , Buckling‑restrained brace (BRB) , Vertical irregularity , Hysteretic behavior , Seismic sequence

Sepideh Shahrivar

Dr. Gholamreza Ghodrati Amiri Dr. Vahid Broujerdian