Constitutive Law of High-Strength Confined Concrete in Structural Members under Flexural Compression

本研究的目的是理想化的应力应变曲线的高强度约束混凝土的成员受弯压。回顾了1997年进行的高强度约束混凝土柱、柱轴向加载试验的结果。根据研究结果，进行了如下分析工作；(1)将围压配筋量和配筋强度评价的最大围压与最大强度处的侧压之比表示为标准钢瓶抗压强度的函数。最大强度下的应变用侧围压与标准圆柱体抗压强度之比表示。导出了约束混凝土在最大强度下的应力和应变作为最大强度下侧围压的函数的公式。(2)建立了钢筋混凝土离散单元约束截面模型。利用该模型进行了数值计算，得到了应力应变曲线。(3)上述数值计算适用于各种型钢配置的截面。(4)通过侧向围压预测最大强度。提出了约束混凝土整体应力-应变曲线的理想化方法。1998年对钢筋混凝土柱进行了双向荷载试验。将试验得到的塑性铰区域弯矩-曲率关系与基于标准圆柱体压缩试验应力-应变曲线模型的分析结果进行了比较。由于将轴向加载试验得到的应力-应变曲线应用于受弯压缩混凝土，因此考虑了试验结果与分析结果的差异。提出了一种能够补偿差值的系数。

The objective of this research is idealization of stress-strain curve of high-strength confined concrete in members subjected to flexural compression.In the year of 1997 experimental results of axial loading tests on high-strength confined concrete cylinders and prisms carried out in the past were reviewed. Based on the results analytical work was conducted as follows ;(1) The ratio of the maximum confining lateral pressure evaluated by the amount and strength of confining reinforcement, and lateral confining pressure at the maximum strength was formulated as a function of the standard cylinder compression strength. The strain at the maximum strength was expressed by the ratio of the lateral confining pressure to the standard cylinder compression strength. A formula giving the stress and strain at the maximum strength of the confined concrete was derived as a function of lateral confining pressure at the maximum strength.(2) A model for confined cross section which consists of concrete and steel discrete elements was developed. Numerical calculation using the model to obtain stress-strain curve was conducted.(3) The above numerical calculation was applied to cross sections with various types of steel configuration.(4) Maximum strength was predicted by lateral confining pressure. Idealization of a whole stress-strain curve of confined concrete was proposed.In the year of 1998 bi-directional loading tests on reinforced concrete columns were conducted. The moment-curvature relationship in the plastic hinge region obtained by the tests was compared with the analytical results which were based on the stress-strain curve model from the standard cylinder compression tests. The difference between the experiment and analyses was, considered due to application of the stress-strain curve obtained by the axial loading tests to the concrete under flexural compression. A coefficient which is able to compensate the difference was proposed.