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

本研究的目的是将高强约束混凝土受弯构件的应力-应变曲线理想化。回顾了1997年高强约束混凝土圆柱体和棱柱体的轴压试验结果。在此基础上，进行了以下分析工作：(1)建立了以配筋量和强度为指标的最大围压与最大强度处的侧向围压之比，作为标准圆柱体抗压强度的函数。最大强度处的应变由侧向围压与标准圆柱体压缩强度之比表示。推导了约束混凝土最大强度时的应力应变公式，作为最大强度时侧向围压的函数。(2)建立了由混凝土和钢离散单元组成的约束截面模型。利用该模型进行了数值计算，得到了应力应变曲线。(3)将上述数值计算应用于各种型钢结构的截面。(4)通过侧向围压来预测最大强度。提出了约束混凝土应力-应变全曲线的理想化。1998年进行了钢筋混凝土柱的双向加载试验。将试验得到的塑性铰区域的弯矩-曲率关系与基于标准圆柱体压缩试验的应力-应变曲线模型的分析结果进行了比较。考虑到试验和分析之间的差异，是由于轴向加载试验得到的应力-应变曲线应用于混凝土受弯压缩。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.