Based On The Size Effect Of Concrete Structures Carrying Capacity Study

The size effect is the basic characteristic of the brittle material and the quasi-brittle material, which performs significantly during the fracture failure of the structure. For the concrete members, the size effect mainly induces the fracture energy's increasing as the dimension increases and the strength inversely. At present, comparing with the research on the concrete material and the plain concrete member, the research on the size effect of the concrete member is still limited.As it is realized that the fictitious crack model can explain the size effect of the concrete well, the fracture mechanics plays a more and more important role in the development and application of the analysis of the concrete fracture. Based on these theories, the bearing capacity of the concrete beam is studied by adopting the criterion of fracture toughness. The contents are listed as follows:At first, the stress intensity factors on the tip of the crack caused by the dead weight of the beam, the load, the reinforcement and the cohesive force on the fracture process zone are calculated. If the sum of the stress intensity factor exceeds the fracture toughness, the crack would increases, vice versa. Then the bearing capacity of the member is obtained by the iterative calculation of the increasing load and length of the crack, which is realized in the Matlab. It shows that although the reinforcement would restrain the crack of the concrete, lead the plastic behavior, the size effect still exists in the reinforced concrete member, which is less obvious than in the plain concrete.Furthermore, through creating some beam models of different dimension with the cohesive element, the crack process of the concrete based on the fictitious crack model is simulated, whose result anastomoses the numerical analysis well.The purpose of the research of the concrete fracture is to build a set of criterions of fracture to describe the crack process quantitatively, so as to apply the size effect to the design of the concrete structure in the future.