混凝土早期约束收缩开裂机理及试验研究

现浇混凝土结构早期开裂是工程中存在的普遍现象,裂缝对建筑物的正常使用、耐久性及结构安全都会产生不利影响。现有混凝土结构裂缝控制的失效准则是基于强度条件的失效准则,本文以断裂力学理论为基础,建立混凝土结构早期约束收缩开裂机理模型,提出早期约束收缩开裂的预测方法及具体步骤。在断裂模型中,应力强度因子及裂缝尖端张开位移试验室测定方法具有明显的尺寸效应,本文基于BP神经网络模型提出断裂参数的预测方法,采用改进型环形收缩试验验证模型的合理性,结果表明本文建立的混凝土早期约束收缩开裂理论模型对结构早期开裂时间的预测结果与试验结果有很好的一致性。

Theoretical and Experimental Study on Early Restrained Shrinkage Cracking of Concrete

Early cracking is a common phenomenon in construction of cast-in-place concrete structures.Early cracking affects the normal use,durability and structural safety of buildings.The existing failure criteria for control of cracks in concrete structures are based on the strength.In this paper,the model of the early restrained shrinkage cracking mechanism is established on the basis of the theory of fracture mechanics,and the methods and steps for predicting early restrained shrinkage cracking are developed.Tests of the notched beam specimen show that the stress intensity factor and crack tip opening displacement are size independent,the new method for predicting fracture parameters is developed on the basis of the BP neural network model.The improved shrinkage ring tests have been done to verit the mechanical model of early restrained shrinkage cracking of concrete structures.The results show that there is good agreement between the experimental results and theoretically predicted results.