Anchorage Performance of Hooked Bars in Reinfored Concrete Members

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In the previous study, the authors classified the anchorage failure of 90-degree hooked bars in exterior beam-column joints at an intermediate story into three modes : a side split failure, a local compression failure and a raking-out failure (named by the authors newly.) The purpose of this study is to clarify anchorage performances for all failure modes, especially for the raking-out failure mode of 90-degree hooked beam bars in exterior beam-column joints.The part one of this report estimates anchorage behavior of the joints at an intermediate floor and proposed some anchorage strength evaluations on the basis of 63 test specimens. The remarks on the rakig-out failure are (1) the strength increased severely according to increase of column axial stress in range of the axial stress ratio less than about one third, (2) since the failure crack lines with a trapezoidal shape in horizontal cross section appeared, the effect of lateral joint reinforcement on the strength reduced in case of large thickness of cover concrete.The part two of this report says the anchorage behavior of joints at a top floor on the basis of 24 knee joint specimens. The conclusions are follows : (1) the anchorage mechanism depends on stress transmission from tail portion of hooks to adjacent column bars, (2) main influence factors on the anchorage strength sre tail length after bent portion, horizontal distances between tail and column bars and between tail bars and beam end, lateral reinforcement ratio in joint and concrete strength, and (3) evaluation formulas on anchorage strength and deformability were proposed.In the part three, the exterior beam-column joints at an intermediate floor were simulated by a non-linear finite element method for reinforced concrete members. The good simulation for the specimen with raking-out failure was obtained by using discrete crack elements and dowel action of column bars at the crack elements.