鋼モルタル板を用いた座屈拘束ブレースの実験的研究: 座屈モード数の評価および圧縮引張耐力比と細長比の関係

摘要

軸圧縮力を受けるブレースは座屈現象を起こし耐力低下を生じるが，拘束材で座屈を拘束することで圧縮域でも引張域と同等の性能を発揮できる座屈拘束ブレースは，その実用化以来多くの構造物に 使用されている．軸方向力を伝達するブレース芯材が座屈しないよう拘束材で補剛した座屈拘束プレースについては，様々な形状の拘束材や芯材を持つ座屈拘束ブレースが提案され，その性能評価や設計法に関して多くの研究例えばが行われてきた．その中の一つとして，筆者らは拘束材に鋼モルタル板（溝形鋼にモルタルを充填したもの）を用いた座屈拘束ブレース（以下，鋼モルタル板型座屈拘束ブレース）を提案し，その性能評価を行ってきている．鋼モルタル板型座屈拘束プレースは図1に示すように両面にアンボンド材を貼付した平鋼芯材を2枚の鋼モルタル板で挟みこむ形式をとる．%The authors have conceived the budding-restrained braces (BRBs) providing stable hysteretic behavior under the high-strain conditions. The compressive strength of BRBs generally tends to be higher than the tensile strength. The authors assumed that it was because of friction force between the surface of core plate and the restraining part, and that the magnitude of friction force was related to the buckling mode number resulting in the increase of contact points. A set of prediction formulas for the buckling mode number has been proposed in the authors' previous study. In this paper, the validity of the proposed formulas for the buckling mode number is examined by the test results of strain gauge measurement on the core plate from the cyclic axial-loading tests. Furthermore, the relationship between the strength ratio of the compressive to tensile strength and the slendemess ratio of plastic region of core plate is estimated. As a result, 1) the progress of the buckling mode shape is successfully observed from the test results, and 2) the proposed formulas correspond approximately to the upper and lower bounds of the buckling mode number and also estimate quite well the strength ratio from the test results.