Determination Of Tensile Strength And Effective Fracture Toughness Of Concrete Based On Fracture Extreme Theory

With the rapid development of economy and the increase of social demand,a variety of large construction projects are increasing.Concrete becomes one of the most widely used materials in constructions due to its wide range of materials,low price and high compressive strength.However,internal defects of concrete and external factors result in cracks in concrete structures,which may affect the usability and safety of structures and even cause great losses to the life and property of the country and people.Considering the quasi-brittle characteristic of concrete,scholars have proposed many nonlinear fracture models to determine the mechanics and fracture parameters of concrete,which have important scientific significance for correctly evaluating the fracture characteristic of concrete structures and solving engineering crack analysis problems.In this study,the crack propagation criterion is strength criterion.Based on fracture extreme theory,a theoretical method for determining the tensile strength and effective fracture toughness of concrete was proposed.The following contents are included.(1)A theoretical method for determining the tensile strength and effective fracture toughness of concrete was proposed.The three-point bending beam was adopted to illustrate the proposed method.The tensile strength and effective fracture toughness of plain concrete and dam concrete were determined by using the proposed method.The reliability of the proposed method was verified by comparing the calculated results to existing analytical methods and test results.The results show that the calculated values of effective fracture toughness are in good agreement with the results obtained by existing analytical method,and are insensitive to the initial notch ratio of specimen.The tensile strength calculated by the proposed method is close to the test value.(2)A theoretical method for determining the tensile strength and effective fracture toughness of concrete was developed with the wedge-splitting specimen.The tensile strength and effective fracture toughness of specimens with different sizes and initial notch ratios were calculated by using the proposed method.And the sensitivity of effective fracture toughness to the initial notch ratio and specimen size was analyzed.The results show that the tensile strength calculated by the proposed method is close to the test value.The effective fracture toughness has no obvious change with initial notch ratio.When the specimen height reaches a certain value,the effective fracture toughness does not change significantly.(3)Combining the advantage and disadvantage of three-point bending beam and wedgesplitting specimen in concrete fracture tests,a new arc bending notched specimen was studied.The expressions of stress intensity factor and crack mouth opening displacement of the proposed specimen were determined by using the superposition method.And four groups of specimens with different initial notch ratios were tested.Finally,based on fracture extreme theory,a theoretical method for determining the tensile strength and effective fracture toughness of concrete was established with the new arc bending notched specimen.The sensitivity of effective fracture toughness to the initial notch ratio was analyzed.The results show that the effective fracture toughness is insensitive to the initial notch ratio of specimen.And the tensile strength calculated by the proposed method is close to the test value.