Development of FEM Concrete Constitutive Model independent from element (mesh) size, and its application to FEM analysis of full scale structural members

本研究主要分为两个阶段。主要结果总结如下：(1)应变软化型混凝土本构模型及三维有限元分析的发展本文建立了较低围压条件下混凝土的应变软化型本构模型。本文首先通过对多个混凝土试验数据的模型参数进行重新检验，将所提出的模型扩展为能够预测混凝土在拉伸和压缩条件下的多轴应力软化行为的模型。随后，在有限元分析程序（FEAP）中实现了所提出的混凝土模型，并对约束混凝土进行了三维有限元参数分析。(2)混凝土软化特性对构件强度影响的有限元分析通过对承压混凝土和钢管混凝土压缩变形特性的三维有限元分析，将目前提出的应力硬化-软化模型与常用的弹塑性本构模型进行了比较。结果表明，考虑混凝土的应变软化特性对构件的预测具有重要意义。(3)进一步研究本研究已经提出了一种在有限元分析中不受网格尺寸影响的方法。然而，一系列的有限元分析仍在进行中，以预测全尺寸结构构件的行为。

There are two main stages in the present study. Main results are summarized in the following.(1)Development of Strain-Softening Type Constitutive Model and 3-D FEM Analyzes for Confined ConcreteThe authors have developed a strain softening type constitutive model for concrete under compression with relatively low confining pressure. In the present paper, firstly the proposed model has been extended to the model which can predict the softening behavior of concrete under multi-axial stresses in tensile as well as compressive condition, by re-examining the model parameters from several experimental data on concrete. Subsequently, the proposed concrete model has been implemented in the finite element analysis program (FEAP) and 3-D FEM parametric analyzes have been performed on the confined concrete.(2)FEM analysis foe Effect of Softening Behavior of Concrete on Strength of Structural MembersComparison has been carried out between the presently proposed stress hardening-softening model and the usually used elastic-perfectly plastic constitutive model, throuhg 3-D FEM anaylsis for the compressive deformation behavior of confined concrete and concrete filled steel tube. Based on the results, it has been confirmed that the concideration on the strain softening behavior of concrete is very important for the prediction of structural members.(3)Further StudyA method to get independent from mesh size in FEM analysis has beeen already proposed in the present study. However, a series of FEM analysis is still being carried out to predict the behavior of full-scale structural members.