Study On Shrinkage Fracture Mechanism Of Concrete Structure Materials

In structural engineering,the shrinkage deformation of concrete is often caused by the decrease of water-cement ratio and weather reasons.As the tensile strength of concrete material itself is relatively low,especially the early strength is lower,it will cause structural cracking when the structure has restraint effect and tensile stress exceeds its ultimate tensile strength of concrete.It is generally believed that macroscopic failure of material structure is caused by the change of mesoscopic elements.Therefore,a macroscopic fracture model is discussed in this paper firstly on its microscopic perspective.Based on dry shrinkage test,the crack formation mechanism of concrete structure and crack resistance of fiber are analyzed under some constraint conditions.And it is compared with the finite element simulation.The main content is as follows(1)The relationship between stress and deformation of micro-cracks in the damage process area before the macro gap,is evaluated based on model of damage zone strip at the macro crack end and the analysis method of micromechanics.The damage factor,the function of mechanical parameters and stress intensity factor are obtained about a fracture process zone.(2)The free shrinkage test of concrete with drying,and the concrete shrinkage of plain concrete and steel fiber concrete with constrain is carried out for drying.And multiple phenomenon of concrete dry shrinkage are obtained for different structures.The finite element software ABAQUS was used to simulate the restricted structure,and it was compared with dry test results,by means of the shrinkage cracking mechanism of restricted concrete.(3)The mechanism of concrete dry shrinkage cracking and the estimation method of dry shrinkage strain are analyzed,and it compared with different dry shrinkage prediction models in the world.For the crack resistance effect of steel fiber on concrete cracking,the mechanical model of fiber bridging were investigated,with the discussion of mechanical property of a single fiber.(4)According to the characteristics of some ring structure,the main factors of cracks formation are discussed for elastic mechanics theory.Then,the dry shrinkage cracking experiment is compared with the finite element simulation of ABAQUS.Based on Nonlinear diffusion theory,the finite element analysis of concrete humidity field is carried out by means of temperature module in ANSYS.