SUMMARYThe authors developed a buckling-restrained brace that enables increased design freedom at both ends of the core plate and strict quality control while providing stable hysteresis characteristics even under high strains. The buckling-restrained brace can be formed by welding a core plate covered with unbonded material to a pair of mortar-filled channel steels (steel mortar planks) as a restraining part. The use of this approach enables visual confirmation of the status of the mortar filling and also facilitates standardizing structural members and member-by-member quality control. Specimens of a buckling-restrained brace with different steel mortar plank heights are fabricated to adjust the restraining force, along with specimens with different core plate width-to-thickness ratios. The tests were conducted to reveal the hysteretic characteristics of the braces, as well as their cumulative plastic strain energy, elastoplastic properties, and stiffening properties. A performance evaluation formula as well as a buckling-restrained brace design method using the test results is proposed.

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The authors have proposed the buckling-restrained braces (BRBs) using steel mortar planks, providing stable hysteretic behavior under the high axial-strain conditions. The compressive strength of BRBs generally tends to be higher than the tensile strength.The authors understood 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 of plastic region of core plate is examined by the test results of strain gauge measurement on the core plate from the cyclically axial-loading tests. Furthermore, the relationship between the strength ratio of the compressive to tensile strength and the buckling mode number is evaluated. As a result, 1) the buckling mode number is approximately proportional to the slenderness ratio of the plastic region of core plate, and 2) the proposed formulas, considering the location of fixed point between the core plate and restraining part, correspond quite well to the test results in the relationship between the compression-to-tension strength ratio and the axial strain amplitude.

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