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Report - PEER - University of California, Berkeley

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(a) interior beam-column joint(b) knee joint underclosing load(c) knee joint underopening loadFigure 2. Behavior model for joint shear failure.the strength, although the quadruple flexural resistance has an essential role to definethe joint shear behavior. So it is not enough to predict joint shear strength consideringthe quadruple flexural resistance, but it is necessary to control the contribution <strong>of</strong> sheardeformation occupied in story drift. Thus, the quadruple flexural resistance wasevolved into a more comprehensive and mathematical model (Shiohara 2004). Themodel considers two sets <strong>of</strong> critical sections associated with two independent deformationmodes, called J-mode and B-mode. J-mode is equivalent to the quadruple flexuralresistance and featured by the diagonal crack as shown in the Fig. 2. This action causesobserved joint shear deformation. So this type <strong>of</strong> resistance and relevant deformation ishereafter called J (joint)-mode. If the J-mode deformation becomes too excessive, concretewill crush adjacent to the crossing point <strong>of</strong> diagonal cracks and cover concretewill spall <strong>of</strong>f. Whereas, B-mode is featured by the cracks along the face <strong>of</strong> column orbeam as contrasted with J-mode in Fig. 3. The increase <strong>of</strong> section curvature due to B-mode deformation primarily causes cord rotation <strong>of</strong> beam or column.The objective <strong>of</strong>the introduction <strong>of</strong> the two modes is to obtain two joint shear strengths calculated fromboth J-mode and B-mode. The two modes <strong>of</strong> J-mode and B-mode usually give differentstrength reflecting a difference in critical sections. The smaller value <strong>of</strong> thestrengths gives the real strength and its mode becomes dominant. Thus prediction <strong>of</strong>dominant deformation mode is feasible by comparing the two strengths.Hence the analytical methods to calculate the strength <strong>of</strong> the both modes are necessary.The method <strong>of</strong> calculation <strong>of</strong> the strengths for J-mode and B-mode is very similarto the classical flexural theory where each section curvature causes momentresistance by a pair <strong>of</strong> force resultants in tension and compression arising in reinforcingbars and concrete.459

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