四点剪切梁法研究混凝土I-II复合型起裂准则及其缝高比影响规律

Study on initial cracking criterion for Ⅰ-Ⅱ mixed mode crack and influence of crack-depth ratio in concrete by using four-point shearing beams

通过对3种不同缝高比试件的四点剪切梁试验,进行了混凝土I-II复合型起裂准则的试验研究,试验过程中除了测得极限荷载外,还测得了各个试件的起裂荷载及起裂角度。根据所测得的起裂荷载并通过有限元方法计算了开裂状态下的应力强度因子KI、KII分量,进而提出了与以往由极限荷载确定的断裂准则相区别的起裂准则,研究了缝高比对该起裂准则、试件起裂角度和应力强度因子分量的影响规律。结果表明,缝高比在0.3～0.4之间,其对混凝土I-II复合型断裂起裂准则有明显的影响;缝高比在0.4～0.5之间,其对混凝土I-II复合型断裂起裂准则基本上没有影响。随试件缝高比的增大,试件的起裂角度会增大,但对KI/KII却随缝高比的增大而减少。

An experimental study on initial cracking criterion has been carried out by using four-point shearing beams with three different crack-depth ratios.The maximum loads,the initial loads and crack initiation angles were measured in the experiment.Based on the initial loads measured in the test,the corresponding KⅠ and KⅡ can be calculated using finite element method.Besides,a more rational load distribution under four-point shearing condition was obtained.Finally,a crack initial cracking criterion for I-II mixed mode crack was proposed,which is different from the cracking criterion by using maximum loads,and its crack-depth ratio effect,crack-depth ratio effect on the crack initiation angles,KⅠ /KⅡ were also discussed.The result shows that when crack-depth ratio in the range from 0.3 to 0.4,it has important effect on crack initial cracking criterion for I-II mixed mode crack,while the crack-depth ratio in the range from 0.4 to 0.5,it has little impact.The test results also show that the crack initiation angles increase with the increase of crack-depth ratio.While for KⅠ/KⅡ,it decreases along with the increase of the crack-depth ratio.