種々のガセットプレートおよび直交小梁を有する座屈拘束ブレースの機構安定性

<p> 1. Introduction</p><p> 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.</p><p> 2. Stability Evaluation Method for BRBs with Different Connections at each End</p><p> The previous evaluation method for BRBs in a chevron configuration adopted several key assumptions:</p><p>  Out-of-plane buckling displacements y_r1 and y_r2 are proportional to initial geometric imperfections a_r1 and a_r2, such that the ratio r_a= a_r1/a_r2 = y_r1/y_r2 remains constant.</p><p>  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.</p><p>  Neck hinge plastic capacities at each end are assumed equal M_p^r = M_p^r1 = M_p^r2.</p><p> The assumption that the displacement ratio r_a remains constant is not valid when the connections at each end substantially differ. A new formulation is derived that relaxes this limitation.</p><p> 3. Calibration and Validation of Numerical Models against Cyclic Experimental Results⁹⁾</p><p> 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.</p><p> 4. Numerical Study of Gusset and Beam Stiffness</p><p> Gusset plates (GPL) with 3 different stiffener arrangements and 5 transverse beam sizes were modelled and the equivalent rotational stiffness evaluated.</p><p> 5. Effect of Gusset and Beam Stiffness on the Buckling Capacity of BRBs in Single Diagonal Configuration</p><p> FEM models with the gussets introduced in Chapter 4 are analyzed and the peak inelastic buckling load is compared to the analytical capacity predicted by Chapter 2. While the error is within 20%, the neck yield limit is predicted within 10%, indicating greater confidence in elastic range.</p><p> 6. Proposal of Inelastic Buckling Amplification Factor α based on Shanley’s Theory</p><p> An inelastic amplification factor α is introduced, defined as the ratio of the peak inelastic buckling load to the neck yield limit. Shanley’s theory is extended to the case where the gusset provides supplemental residual elastic stiffness after the neck has yielded. This is compared to the FEM results and found to predict the peak inelastic buckling load within 20%.</p><p> 7. Effect of Gusset and Beam Stiffness on the Buckling Capacity of BRBs in Chevron Configuration</p><p> The analysis from Chapter 5 is extended to the chevron configuration using the beams from Chapter 4. The evaluation method from Chapter 6 is in good agreement with the FEM results, with errors within 20%.</p>