Numerical Simulations And Studies On Fracture Behaviors Of Concrete With Defects

Concrete has many advantages,including wide sources of raw materials,simple construction techniques and easy to shape and so on,so it is widely used in civil engineering,hydraulic engineering and other infrastructure constructions.However,due to some natural defects,such as crack,air void and weak interfacial transition zone(ITZ)and so on,the durability and fracture resistance of concrete will be obviously weakened.Therefore,it has a great of academic value and engineering significance to study the effects of these defects on the anti-fracture capacity of concrete.After the reasonability of numerical simulation methods were verified by comparing with the corresponding experimental results,they were used to study the effects of various defects on the fracture properties and behaviors of concrete.The important innovative contributions are as follows.(1)The three point bending(TPB)facture behaviors of concrete beams with a prefabricated notch or two prefabricated notches were investigated.And the dead or living problem of a notch was discussed.Firstly,the TPB fracture experiments were conducted on the concrete beams with a single notch and double notches,and the load-displacement curves and crack paths were obtained.Then,using the improved random aggregate generation and packing algorithm,a series of 2D two-phase mesoscale heterogeneous concrete beam models were established.By combining with the cohesive zone model(CZM),the fracture behaviors of concrete beams under TPB load were simulated.After the numerical method was verified by comparing the simulated load-displacement and crack paths with the experimental ones,the effects of the notch location and distribution of aggregates on the dead or living problem of a notch in a double-notch beam were studied using the numerical method.It was found that the notch location is the main influence factor.A notch closer to the mid span of the beam is more easily to be activated.(2)The air void induced fracture in a heterogeneous concrete beam under TPB was simulated using the extended finite element method(XFEM).Firstly,the TPB tests of concrete beam with a prefabricated through hole were carried out,and the change of load and acoustic emission events curves with the displacement were obtained.Secondly,the XFEM simulation was verified by qualitatively and quantitatively comparing the numerical with experimental results.Finally,the effects of air void location and size on the fracture behaviors of concrete were researched using XFEM.The results showed that when an air void is nearer to the mid span and bottom of beam,it weakens the fracture resistance more considerably.(3)The conception of air void affected zone can was proposed,and the effect of void on the fracture path of concrete beam with a single edge notch under symmetrical four point bending load was studied using the numerical method.Firstly,it was assumed that the shape of void affected zone is circular.The radius of void affected zone was determined by moving the void along the length of beam until the crack does not go through the void.Secondly,the effects of void size and distance between the center of void and the bottom of beam on the size of void affected zone were analyzed,and the dimensionless void affected zone was fitted as a function of the dimensionless void size and location.Finally,as validation,the fitted function was used to explain the choice of crack path in multi void concrete beam models.(4)The fracture behaviors of heterogeneous concrete under uniaxial tension were studied,and the effects of randomness of ITZs properties on the dispersion and distribution characteristics of fracture performance of concrete were discussed.Firstly,the simulated stress-strain curve was compared with the experimental results in the exciting literature.Secondly,it was assumed that the mechanical parameters of ITZs obey a normal distribution.With the statistical method,the effects of randomness properties on the dispersion of peak load,dissipated fracture energy and fracture morphology of concrete were analyzed.The distribution types of peak load and dissipated fracture energy were also analyzed.The results showed that due to the effects of randomness parameters of ITZs,the peak load and dissipated fracture energy of concrete approximatively follow a normal distribution or a Weibull distribution.In the three parameters of ITZs,the randomness of tensile strength has the greatest influence on the dispersion property of concrete fracture.