Clarification of Out-plane Shear Resisting Mechanism of Planer Member and Design

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In this year the objectives were- evaluation of influence of shear reinforcement amount on punching shear strength- establishment of a macro model for out-plane shear resisting mechanism using nonlinear finite element analyzesThe results are summarized as follows :1 In order to clarify the influence of shear reinforcement amount, two-way slabs were tested in which shear reinforcement amount was varied from 0 to 0.34% by varying number of deformed stirrups with the same diameter. Although apunching shear strength in the case without the stirrup was understimated by the equations in CEB/FIP Model Code 90 (The equation in JSCE's Standard Specification estimated it reasonably.), increments in the punching shear strength with increase in shear reinforcement amount was estimated approximately. For the cases of small amounts of shear reinforcement (0.11 and 0.23%) the ovserved strength increments were less than the predicted ones probably because the stirrups were placed at too big spacings.2 Since variation of punching shear strength due to variation of tensile reinforcement stiffness (ratio times elastic modulus) is the same as that of shear compression strength of linear members, a new macro model was proposed applying the shear resisting model for linear members which was derived from numerical experiments with nonlinear finite element analyzes to planer members (slabs). This model consists of shear resisting of concrete in compression zone and shear resisting in shear cracking zone. It is necessary to quantify sizes and critical stresses of the two zones.Presently a constitutive model for concrete subject to tri-axial stresses is being implemented into the program of the nonlinear finite element analysis. It is mecessary to establish a macro model for shear resisting in which unclarified parameters, such as loading area configuration and shear span to depth ratio, are considered, conducting numerical and experimental analyzes.