确定混凝土开裂与拉伸强度及双K断裂参数

该文考虑混凝土材料的非均质特性，发展了确定无尺寸效应的混凝土开裂强度与起裂韧度、拉伸强度与断裂韧度等材料参数的断裂理论与相应方法。基于三点弯曲、楔入劈拉、四点弯曲等不同类型混凝土试件的断裂试验，确定出对应的开裂强度与起裂韧度、拉伸强度与断裂韧度等材料参数，并与试验强度值及由双K断裂模型确定的双K断裂参数进行了比较，从而验证了所提模型与方法的合理性与适用性。基于确定的材料参数，分别建立了混凝土起裂与断裂破坏的全曲线，给出了确定无尺寸效应起裂韧度的混凝土试件最小理论尺寸。建立了起裂荷载与起裂韧度之间的解析公式，对三点弯曲、楔入劈拉、四点弯曲等不同类型混凝土试件的起裂荷载，以及不同混凝土的起裂韧度进行了成功预测。

DETERMINATION OF THE CRACKING STRENGTH,TENSILE STRENGTH AND DOUBLE K FRACTURE PARAMETERS OF CONCRETE

It presents an improved fracture theory and an associated method for determining the independent material parameters of concrete, e.g. cracking strength, initial fracture toughness, tensile strength and fracture toughness for different types of specimens, in which the heterogeneous properties of concrete were considered. Based on the concrete fracture tests of three-point-bending (3-p-b), wedge-splitting (WS) and four-point-bending (4-p-b) specimens, the corresponding cracking strength, initial fracture toughness, tensile strength and fracture toughness were simultaneously determined. The rationality and applicability of the proposed model and the associated method were verified by the experimental concrete strength and the double K fracture parameters determined by the double K model. The whole initial fracture curves and fracture failure curves of concrete were obtained using the determined materials. The theoretical minimum concrete specimen size for determining the initial fracture toughness to meet the condition of linear elastic fracture mechanics was given. Based on the proposed simple analytic expressions between the cracking strength and the initial fracture toughness, the initial loads of all 3-p-b specimens, WS specimens and 4-p-b specimens were successfully predicted. The initial fracture toughness of concrete was also determined using the analytic expressions.