大規模な超高層建物や空間構造物への適用を目的にBRBの長尺化が進んでおり，その寸法効果がBRBの破壊モードや履歴特性，累積変形性能に与える影響の再検証が必要と考えられています。特に板厚-塑性化部長さ比Lp/tc≧400の矩形断面の長尺BRBでは，(1)芯材との摩擦の繰返しにより剥離材が損傷し摩擦に起因する圧縮力が徐々に上昇し，(2)材軸方向に偏在する圧縮歪とポアソン比に従って芯材断面が無視できないほど増大すると，芯材と拘束材の間隙が閉塞して圧縮力が急激に上昇する新たな現象(Core binding)が発生し，(3)引張に対する圧縮力の耐力上昇率βが各種基準値を超える場合があることが数値解析的に明らかされており，本研究では，長尺を含む実大BRBの準静的漸増繰返し載荷実験を実施し，BRBの寸法効果がその破壊モードや履歴特性，累積変形性能に与える影響を検証するとともに，Core binding発生歪の推定法や既往の疲労破壊評価法の適用性を検証しました。(準静的ですが)実大実験でCore bindingの発生を確認したのは世界初と思われます。本研究は日鉄エンジニアリング株式会社との共同研究成果であり，一部にJSPS若手研究(No.21K14288)，JSPS基盤研究(B) (No.24K01022)，JSPS基盤研究(A)(No.21H04581)および東京科学大学令和5年度環境・社会理工学院共通経費による顕彰と研究助成の助成を戴きました。ここに記して感謝申し上げます。
Buckling-restrained braces (BRBs) are widely used as energy-dissipation members in seismic areas, and BRBs with 10–20 m workpoint lengths have been applied in practice, particularly in tall buildings and spatial structures. According to the previous numerical investigation, higher mode buckling and friction were shown to significantly amplify the compressive strain at the core ends and tensile strain at midspan, in part due to cyclic strain ratcheting, introducing the potential for core binding and premature necking. Therefore, in this study, a series of quasi-static full scale test was carried out to investigate the effect of the core length and cross section on the hysteresis and the low-cycle fatigue capacity of BRBs. As a results, the numerically predicted new fracture modes (the friction-induced core binding and significantly increment of compression overstrength) of the long BRBs were experimentally observed for the first time. Finite element models were subsequently calibrated to the test specimens to further analyze the observed fracture modes and to investigate the local strain and stress value on the core plate in detail. This work was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science Fellowships (No. 21H04581, 21K14288 and 24K01022).