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

本年度的研究目标是——评价抗剪配筋量对冲切抗剪强度的影响——利用非线性有限元分析建立抗面外抗剪机理的宏观模型。研究结果如下：1为了明确抗剪配筋量的影响，通过相同直径的不同数量的变形箍筋，对抗剪配筋量在0 ~ 0.34%范围内变化的双向板进行了试验。虽然CEB/FIP模型规范90中的公式低估了无箍箍情况下的冲孔抗剪强度（JSCE标准规范中的公式对其进行了合理的估计），但随着抗剪配筋量的增加，冲孔抗剪强度的增量是近似估计的。当配筋量较小（0.11%和0.23%）时，观察到的强度增量小于预测值，可能是由于箍筋间距过大针对钢筋抗拉刚度（弹性模量的比值）变化引起的冲剪强度变化与线形构件抗剪强度变化相同的特点，提出了一种基于非线性有限元数值试验的线形构件（板）抗剪模型的宏观模型。该模型由混凝土受压区抗剪和抗剪开裂区抗剪组成。有必要量化这两个区域的大小和临界应力。目前，三轴应力作用下混凝土的本构模型已被应用到非线性有限元分析程序中。有必要建立一个考虑加载区配置、剪切跨深比等未明确参数的宏观抗剪模型，进行数值和实验分析。

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.