双K断裂模型失稳韧度KIcun的解析计算方法

为预估最大荷载P_max和失稳韧度K^un_Ic,提出一种只需混凝土轴心抗压强度f_c即可计算双K断裂模型失稳韧度K^un_Ic的解析计算方法。大量的试验数据表明,临界裂缝扩展量与韧带高度之比Δa_c/(h-a₀)趋于常数。结合这一规律,基于虚拟裂缝的双线性本构关系,根据带切口的三点弯曲梁跨中截面的平衡条件,计算最大荷载P_max,再将P_max的计算值代入公式计算双K断裂模型的失稳韧度K^un_Ic。为检验计算精度,将最大荷载P_max和失稳韧度K^un_Ic的计算值与试验值比较。结果表明:最大骨料粒径d_max≤40 mm的较大尺寸三点弯曲梁试件,最大荷载P_max及失稳韧度K^un_Ic的计算值与试验值吻合良好。

Analytical Calculation Method for Unstable Toughness of Double-K Fracture Model

An analytical method which merely needs the axial compressive strength f_c of concrete to calculate the unstable toughness K^un_Ic of double-K fracture model is proposed in this paper. Massive experimental data indicate that the ratio of critical crack propagation length Δa_c to ligament length (h-a₀) tends to be a constant. According to this regularity and on the basis of the bilinear constitutive relationship of the fictitious crack model, the maximum load P_max of three-point bending notched beam is calculated under equilibrium condition. Then the calculated result of P_max is substituted to the formula and the unstable toughness K^un_Ic of double-K fracture model is calculated. The calculated results of P_max and K^un_Ic are compared with those of test values to verify the accuracy of the method. Results conclude that the calculated results of P_max and K^un_Ic agree well with test values for relatively big size concrete specimens with maximum aggregate size not greater than 40 mm. The maximum load P _max and the unstable toughness K^un_Ic can be predicted by the proposed analytical method.