Seismic Retrofitting of Reinforced Concrete Buildings with Buckling-Restrained Braces (BRBs) with a Technical Focus on Vertical Irregularity

The aim of this paper is to evaluate the effectiveness of buckling-restrained braces (BRBs) in improving the seismic performance of reinforced concrete (RC) buildings with and without vertical irregularity. To this end, two RC buildings with 5 and 8 stories were first modeled and designed in SeismoStruct as vertically regular systems and then with a mass irregularity applied at the roof level (a 50% mass increase). Following an initial design in accordance with Iranian Standard No. 2800 (5th Edition) and ACI 318-19, the buildings were retrofitted using BRBs with an A36 steel core and a confining concrete cover, and were subjected to nonlinear static (pushover) analysis. The results indicate that, for the regular 5-story building, BRBs reduce base shear by 42% (from 1,850 kN to 1,070 kN) and decrease roof displacement by 55% (from 22 cm to 9.8 cm). For the 8-story building with vertical irregularity, BRBs reduce base shear by 58% (from 3,200 kN to 1,344 kN), reduce roof displacement by 67% (from 48 cm to 16 cm), increase absorbed energy by a factor of 3.2 (from 450 kJ to 1,440 kJ), and enhance the ductility factor from 3.8 to 8.9. Moreover, BRBs compensate for up to 75% of the adverse effects associated with vertical irregularity, such as stress concentration at the top story. The paper underscores the importance of BRBs as an effective, minimally invasive, and economical retrofit strategy for existing RC buildings—particularly those with vertical irregularities—and recommends considering this system in national seismic rehabilitation programs (e.g., for schools and hospitals).