Rational Constitutive Laws to Describe Creep and Shrinkage of Concrete at Elevated Temperatures

自20世纪50年代后期以来，预应力混凝土核反应堆安全壳的发展要求了解混凝土在高温下的力学行为。高温下混凝土徐变和收缩的数学模型。核反应堆结构安全的有限元分析特别需要100 μ C。为此，许多实验研究已经尝试和各种数学模型已被提出作为本构关系的有限元分析。然而，他们中的大多数都未能模拟实验结果。水分含量和运动对机械性能如杨氏模量、收缩和蠕变行为的影响即使在100 ° C以下以及100 ° C以上也是显著的。因此，研究混凝土中的水分迁移对于了解混凝土在高温下的力学性能是非常重要的 ...更多信息 s得到：（1）.通过砂浆和混凝土圆柱形试件在不同温度环境下的试验，研究了水分迁移过程及弹性模量、抗压强度、抗拉强度等力学性能的变化，并将水分迁移结果作为非线性扩散过程进行了有限元分析，对所得材料参数进行了讨论。（二）、采用薄壁圆筒试件，研究了水泥石在高温下的水分迁移和收缩过程。结果表明，收缩与失水量的关系存在一定的变化点，随着温度的升高，这种变化趋势更加明显。（三）、混凝土徐变的双幂律系数受混凝土含水量的影响。为了发展一个通用的本构关系来合理地描述混凝土的徐变，这些系数应该作为含水量的函数给出。少

Since the late of 1950's, the development of prestressed concrete nuclear reactor containment vessels has demanded the knowledge of mechanical behavior of concrete at high temperatures. Mathematical models for creep and shrinkage of concrete at temperatures over. 100^ﾟC have been asked particularly for finite element analysis of the safety in nuclear reactor structures. For this purpose, numerous experimental studied have been tried and various mathematical models have been proposed as the constitutive laws for the finite element analysis. Most of them, however, have failed to simulate the experimental results. The influence of moisture content and movement on the mechanical properties such as Young's modulus, shrinkage and creep behavior is significant even under 100^ﾟC as well as over 100^ﾟC. Therefore, it is very important to study the moisture migration in concrete for understanding the mechanical properties of concrete at elevated temperatures.In this project, the following result … More s are obtained:(1). Cylindrical specimens of mortar and concrete were tested under several temperature atmosphere to study the moisture migration process and changes of mechanical properties such as modulus of elasticity, compressive strength, tensile strength and so on. Moreover, these results of moisture migration were analyzed by a finite element method as a nonlinear diffusion process and the obtained material parameters were discussed.(2). By means of thin wall cylinder specimens, the moisture migration process and shrinkage of hardened cement paste at elevated temperatures were studied. It was shown that the the relationship between shrinkage and water loss had some changing points and this tendency became more clear as the temperature increased.(3). Coefficients of the double power law for creep of concrete are influenced by the moisture content in the concrete. In order to develop a generic constitutive law to describe rationally the creep of concrete, these coefficients should be given as functions of the moisture content. Less