The Research Of Net Stress Intensity Factor On Concrete Crack Tip For Multiple Specimen

At present in the field of concrete fracture mechanics., fictitious crack model, which has a profound effect on concrete researches, greatly inspires scholars. Many model theories in such field are derived form virtual crack models. Among other things the important hypothesis that supports the model theory is that the net stress intensity factor of crack tip equals 0.On the theoretical base of the double-AT criteria and new Kr resistance curve, this paper fully demonstrates whether the net stress intensity factor of concrete crack tip equals to zero by the measure of both theories and experiments, and put forward new viewpoints discovered and summed up in the process of researches, the main points are as follows:1. Discuss and analyze the net stress intensity factor of concrete crack tip ≠ 0 from the viewpoint of both new Kr resistance curve theory and twin-K facture parameter theory.2. Experiments on wedging and splitting apart as well as three-point bent beam were conducted during the experimental study, and test pieces were divided by height into seven groups (150mm, 200mm, 400mm, 600mm, 800mm, 1000mm, 1200mm) and five groups (150mm, 200mm, 300mm, 400mm, 500mm) respectively and the same height ratio of initial cracks, 0.5, was used. The computing result shows the net stress intensity factor of concrete crack tip ≠ 0.3. In the process of researches were found a special point, i.e. "Pi, load point" on the characteristic curve of concrete materials and a more adventurous assumption was put forward in respect of actual application of the twin-K fracture theory in construction projects. In another word, the initial cracking point of macro cracks Pini and the crack length with certain microcrack propagation are introduced to calculate the initial cracking toughness KiniIc. Such a calculation results in a little bit larger Kini Ic, which will give much better play to the performance of concrete materials, however as to the structures of a great importance, we may calculate Kini Ic as a yardstick of crack propagations by means of Pini and ao, the original cracklength.4. The original proposal and method defined in this paper deserves being popularized as well.5. This paper has proved and concluded through both theories and experiments that the net stress intensity factor of concrete crack tips ≠ 0, and left a topic as well to be further researched in depth, that is the generation time of the cohesion distributed over crack tipso...