IJE TRANSACTIONS B: Applications Vol. 32, No. 11, (November 2019) 1591-1609 Please cite this article as: P. Amirsoleimani, A. Panahi, G. Ghodrati Amiri, E. Darvishan, Comparison of Seismic Behavior of BRB and YBS Braces in Irregular and regular Steel Frames under Mainshock and Mainshock-Aftershock, International Journal of Engineering (IJE), IJE TRANSACTIONS B: Applications Vol. 32, No. 11, (November 2019) 1591-1609 International Journal of Engineering Journal Homepage: www.ije.ir Comparison of Seismic Behavior of Buckling-restrained Braces and Yielding Brace System in Irregular and Regular Steel Frames under Mainshock and Mainshock- Aftershock P. Amirsoleimani a , A. Panahi a , G. Ghodrati Amiri* b , E. Darvishan c a School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran b Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran c Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran PAPER INFO Paper history: Received 23 June 2019 Received in revised form 21 August 2019 Accepted 12 September 2019 Keywords: Buckling-Restrained Brace Yielding Brace System Incremental Dynamic Analysis Fragility Curve ABSTRACT Due to low stiffness of braces after yielding, the structures with buckling-restrained braces (BRBs) experience high residual drifts during an earthquake, which can be intensified by aftershocks and causes considerable damages to structures. Also, due to poor distribution of stiffness, this problem is exacerbated for irregular structures. Recently, the yielding brace system (YBS) has been introduced; which is an alternative to BRBFs to solve this problem. YBS has a secondary stiffening part in its hysteresis behavior which can prevent excessive deformations. Therefore, structures with YBS are expected to show a better peroformance in seismic sequences compared to BRBs. However, the seismic behavior of the YBS system in irregular structures has not been studied so far. On this basis, this paper investigates the seismic behavior of frames with BRB and YBS in regular and irregular structures under seismic sequences. Twenty four 4-, 8-, and 12-story frames with these two systems were designed and evaluated. First, a nonlinear dynamic analysis was conducted on the frames under mainshocks, and the maximum interstory drift and the residual interstory drift of the frames were compared. Then, using incremental dynamic analysis and fragility curves, the behavior of the frames under mainshocks was investigated. Afterwards, using incremental dynamic analysis and fragility curves, the behavior of the structures under mainshock-aftershock in three performance levels was also investigated. The results showed that YBS bracing, especially in low rise structures, leads to far lower maximum drifts and maximum residual drifts than BRB braces, which can reduce the probability of the occurrence of soft stories in structures. doi: 10.5829/ije.2019.32.11b.11 1. INTRODUCTION 1 Concentrically braced frames are one of the building systems, which are very popular because of their ease of implementation and their cost-effectiveness in dealing with earthquake forces. However, these systems have behaved well against the earthquakes in recent decades. They have lower ductility and energy absorption capacity as compared to the moment-resisting frames. The main problem with these braces is their buckling under *Corresponding Author Email: ghodrati@iust.ac.ir (G. Ghodrati Amiri) compressive forces leading to differences between compressive and tensile strengths of these braces and decreased strengths of them under compressive forces leading to differences between compressive and tensile strengths of these braces and decreased strengths of them under cyclic loading. Accordingly, buckling-restrained braces were introduced in 1989 for the first time, in which compression buckling of bracing could be avoided by its confinement [1]. Buckling-restrained braces yield in tension and compression, showed an ideal hysteretic behavior [2]. Therefore, the residual drift is unpredictable