GLOBAL STABILITY OF CHEVRON BUCKLING RESTRAINED BRACED FRAMES WITH VARIOUS GUSSET PLATES AND SECONDARY BEAMS

1. Introduction Global out-of-plane stability of buckling-restrained braces is often governed by yielding of the neck. The authors previously proposed a method9) to evaluate this buckling mechanism, including the gusset rotational stiffness, connection length and neck - restrainer flexural continuity. While the proposed method has shown good agreement with experimental and numerical studies, this paper revisits a key assumption in the derivation, where the neck is modelled as an elasto-perfectly plastic hinge. Detailed FEM studies of a chevron BRB experiment with a range of gusset and framing boundary conditions are conducted, and an inelastic buckling model inspired by Shanley’s theory introduced. 2. Stability Evaluation Method for BRBs with Different Connections at each End The previous evaluation method for BRBs in a chevron configuration adopted several key assumptions:  Out-of-plane buckling displacements yr1 and yr2 are proportional to initial geometric imperfections ar1 and ar2, such that the ratio ra= ar1/ar2 = yr1/yr2 remains constant.  Buckling limit is determined from the ultimate strength, at the point at which the combined axial and moment demands exceed the critical hinge plastic capacity.  Neck hinge plastic capacities at each end are assumed equal Mpr = Mpr1 = Mpr2. The assumption that the displacement ratio ra remains constant is not valid when the connections at each end substantially differ. A new formulation is derived that relaxes this limitation. 3. Calibration and Validation of Numerical Models against Cyclic Experimental Results9) A detailed shell model of the chevron BRBs, gussets and frame was assembled, and the rotational stiffness of the transverse secondary beams, torsional stiffness of the primary beam and flexural stiffness of the gusset plate validated against the experimental stiffness obtained from static pull tests. The cyclic out-of-plane buckling of the FEM and experimental models are in good agreement, with the peak inelastic buckling load matching within 10%. Using the calibrated FEM model, it is demonstrated that the monotonic buckling capacity is slightly larger than the cyclic buckling capacity. 4. Numerical Study of Gusset and Beam Stiffness Gusset plates (GPL) with 3 different stiffener arrangements and 5 transverse beam sizes were modelled and the equivalent rotational stiffness evaluated. 5. Effect of Gusset and Beam Stiffness on the Buckling Capacity of BRBs in Single Diagonal Configuration FEM models with