Out‐of‐plane stability assessment of buckling‐restrained braces including connections with chevron configuration

Abstract

SUMMARYOne of the key limit states of buckling-restrained braces (BRBs) is global flexural buckling including the effects of the connections. The authors have previously proposed a unified explicit equation set for controlling the out-of-plane stability of BRBs based on bending-moment transfer capacity at the restrainer ends. The proposed equation set is capable of estimating BRB stability for various connection stiffnesses, including initial out-of-plane drift effects. However, it is only valid for symmetrical end conditions, limiting application to the single diagonal configuration. In the chevron configuration, the out-of-plane stiffness in the two ends differs because of the rotation of the attached beam. In this study, the equation set is extended to BRBs with asymmetric end conditions, such as the chevron configuration. Cyclic loading tests of the chevron configuration with initial out-of-plane drifts are conducted, and the results are compared with the proposed equation set, which is formulated as a function of the normalized stiffness of the attached beam.

Bidirectional substructure pseudo‐dynamic tests and analysis of a full‐scale two‐story buckling‐restrained braced frame

“… The specimen exhibited stable hysteretic behavior under the bidirectional pseudo‐dynamic and cyclic loadings despite fractures at the gusset‐to‐column interfaces during the cycle to SDR = 3.0%. The BRB loads redistributed to the gusset‐to‐beam interfaces upon fracture, which increased the shear in the beam and shear tabs and eventually led to failure at the beam near gusset 3. Stability was compared with the Takeuchi et al method, showing consistency with the experimental response. No instability was observed despite the reduction in gusset rotational strength and stiffness following the gusset‐to‐column interface fractures, indicating that the method can conservatively predict instability. Frame action on the gussets was significant and increased the gusset‐to‐column and gusset‐to‐beam interface demands by an average of 69% and 83% respectively.…”

“…The buckling strength of the connections without bending moment transfer capacity ( N r cr ) is estimated based on the equivalent slenderness ratios of the connections. The global elastic buckling strength of the BRB including gusset plate rotational stiffness ( N B cr ) is estimated with equations 5 to 12 in . These values are dependent on the restrainer bending stiffness ( EI B ) and connection bending stiffness ( γEI B ).…”

“…However, there was no noticeable loss of strength, stability or resilience, with the BRBs fracturing at story drift ratios (SDRs) of 3.6% and above. Research has also been undertaken by Takeuchi et al , who proposed a set of equations to evaluate BRB stability based on the end connection stiffness and out‐of‐plane frame deformation. The equations were verified through testing of BRB frame specimens loaded cyclically with an out‐of‐plane SDR = 1.0%.…”

“…This paper describes the design and performance of the two‐story bidirectional test conducted at NCREE in 2005. The response of the system is compared with (1) the stability assessment proposed by Takeuchi et al and (2) gusset plate design considering frame action. Because of the unique pinned beam‐to‐column connection, frame action demands were determined through a finite element model, which are compared with existing design methodologies for fully welded beam‐to‐column connections.…”

“…Because of the unique pinned beam‐to‐column connection, frame action demands were determined through a finite element model, which are compared with existing design methodologies for fully welded beam‐to‐column connections. Particularly, this paper answers the following: How did the BRB test specimen perform under bidirectional loading? How do the results compare with the Takeuchi et al stability evaluation methodology? How did frame action affect gusset plate demands? How can BRB frames be designed to ensure BRB and gusset plate stability? …”