Damage concentration effect analysis of buckling-restrained braced frames after yielding of the braces
Feng Yulong1 Wu Jing2 Chong Xun1 Meng Shaoping2
1. Hefei University of Technology, Hefei 230009, China;
2. Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing 210096, China
Abstract：The post-yield stiffness of a buckling-restrained brace (BRB) is low. The yielding of the BRBs at one story or multiple stories may cause the stiffness mutation of stories after the buckling-restrained braced frame (BRBF) goes into the elastic-plastic stage. Consequently, the frame moment may redistribute with the damage mechanism of the frame being affected. A weak beam-strong column calculation formula is proposed based on the moment ratio of column end. The formula shows that the demand of column-beam strength ratio is at least equal to 1 (the minimum value) when the moments of the upper and lower column ends at frame joint are equal and have the same directions, while the demand is infinite when the moments are equal, but have opposite directions. Furthermore, the influences of the BRB stiffness ratio of stories on the moment distribution of two-story BRBF are analyzed, disclosing that the yielding of the BRBs at one story in the BRBF can lead to significant change of the moment ratio of lower and upper column ends of frame joint at this story, and the moment of upper column end of the joint may even reverse its direction and increase. Therefore, the BRBF is susceptible to inter-story column hinge mechanism after the yielding of braces. Lastly, the proposed weak beam-strong column calculation formula and moment distribution law of BRBFs are verified via examples. Additionally, the examples show that when the stiffness ratio of BRB-frame is relatively large or the strength ratio of frame column-beam is relatively small, the damage concentration effect of BRBF is more evident.
