Experimental Study On Multi-fracture Fracture Of Concrete Beams

Cracks are the biggest hidden dangers of concrete structure,around concrete cracks has always been the focus of domestic and foreign scholars.The destruction of concrete structure is a complex problem involving mechanics and materials science.The concrete fracture mechanics is a discipline devoted to the cracking of concrete,which introduces many new concepts and methods for fracture problems,which are more suitable for concrete materials than other conventional strength theories.It focuses on the initial defects of the concrete material itself,Analyzes the development law of this initial defect under the action of load,and then puts forward the fracture safety design criteria.Aiming at the problems existing in the research of concrete fracture problem,this paper has done the following work through experimental research and numerical simulation:(1)Compared with other mature engineering disciplines,concrete fracture mechanics is still a developing field,many of its research is not yet mature.In this paper,based on the research results of concrete fracture theory,the three-point bending fracture test with a span-depth ratio S/D = 4,during the test,the load-crack mouth opening displacement(P-CMOD curve)and the load-displacement curve(P-? curve)were collected.The fracture energy of the three-point bending specimen was calculated by using the P-?curve,and the concrete fracture toughness was calculated according to the test data.(2)Due to the complexity of the problem of multi-cracks in concrete,the three-point bending and four-point bending tests of multiple prefabricated multi-crack concrete beams are carried out,and explored the failure load and crack direction of the specimen under different loading modes.During the test,the displacement-crack opening curve(P-CMOD curve)of each crack was collected.Through the curve analysis,we can clearly understand the progress of each crack at the same time,and also record the destruction of morphological map.(3)According to the basic data of the test,establish the numerical calculation model,based on the cohesive fracture model method,the numerical simulation of the specimen is carried out and compared with the experimental results.The results show that the numerical simulation is in good agreement with the experimental results,validated the correctness of the model used.