Experimental Study On The Fractal Propagation Of Reinforced Concrete Beams Subjected To Shear

The crack propagation of concrete structures under load will affect the bearing capacity,deformation performance and other physical and mechanical properties and service life of the members.Therefore,the study on the law of crack propagation of reinforced concrete members is of great significance for the damage assessment and prediction of members and the design of members.Reinforced concrete beam shear failure in the process of the internal stress state is complex,most of the surface cracks areⅠ-Ⅱcomplex cracks,due to the shape of surface crack is not artifacts rules and linear and ignoring the traditional fracture mechanics crack propagation path twists and turns of the details,it is difficult to get accurate results.For accurate research to the geometrical characteristics of the concrete beam shear crack,and its quantitative,this paper uses the fractal theory to analyze the shear crack.In this paper,nine reinforced concrete beams with different shear span ratio and stirrup reinforcement ratio were subjected to shear tests,and the geometric characteristics of the cracks in the shear beams were studied by using fractal theory,and the distribution characteristics of cracks were quantified.The influences of shear span ratio and hoop ratio on crack propagation of shear beam are analyzed.The results are as follows:1.The fractal dimension of the surface crack of the shear beam increases linearly with the increase of the load,and the fractal dimension ranges from 0.9951 to 1.2888,and the fractal dimension increases faster with the increase of the shear span ratio,and tends to decrease with the increase of the stirrup reinforcement ratio.2.The study shows that there is a good quantitative relationship between the fractal dimension of the surface crack of the shear beam and the physical and mechanical performance parameters of the test beam,such as mid-span deflection,maximum crack width and damage variables,and that the mid-span deflection,maximum crack width and damage variables are positively correlated with the fractal dimension of the crack.3.The fractal dimension of the crack is greatly affected by the shear span ratio when the shear beam is destroyed.When the shear span ratio is 1.5,the fractal dimension is lower than 1.23,when the shear span ratio is 2,the fractal dimension is about 1.26,and when the shear span ratio is 2.5,the fractal dimension is above 1.28,which indicates that the fractal dimension can be used as a sign when the test beam is near failure.4.Using the fractal dimension of crack of artifacts can fracture parameters are revised,obtained based on the fracture section of fracture can be G_r/γand surface crack fracture dimension G_d/G_r,and obtained the shear fracture process of concrete beams can fracture parameters change rule,studies show that fractal dimension of crack with load increase,drive the crack to carry out the energy needed to increase.