Prediction Of Concrete Strength Based On Energy Balance Relation During Unloading At Failure

Concrete is a kind of widely used construction engineering materials,and its damage strength and deformation mechanical behavior have always been the basic issues of great concern in the fields of materials science and structural engineering.As far as the physical mechanics model is concerned,the failure conditions of concrete have not been well understood.This article proposes a way to find a solution by describing the energy balance at a point on the damage surface.When the damage is about to occur,a point on the failure surface is subject to the normal stress ?n and tangential stress ?n caused by external forces.Once the failure occurs,the point will be divided into two parts by the new crack,and the normal stress ?n and tangential stress ?n disappear with the formation of the crack.This is an elastic unloading process associated with the occurrence of damage.According to the principle of energy balance,it can be inferred that the elastic strain energy released when the normal stress ?n and the tangential stress ?n are released will be converted into the surface energy of the newly generated crack.Based on this understanding,this paper starts with the equilibrium conditions of the elastic unloading energy of a point on the failure surface and the surface energy of the new crack during the failure of the concrete.The plane in which it is located determines the actual phase in which the failure occurred.An energy description relationship of the failure criterion is established,which is the general expression of the failure condition in the principal stress coordinates.The material parameters involved in this expression have clear physical meanings,and provide new ideas for revealing the failure strength and failure behavior of concrete.For the concrete plane stress problem,the main equation of the failure criterion proposed in this paper contains two parameters in form,namely the material constant k determined by the ratio of the material's shear modulus and bulk modulus and the pure shear failure strength of the material ?0.The piecewise function expression of the main equation under the plane stress state is given,and the approximate assumption of the parameter k is constructed to prove the correctness of the energy balance intensity relationship proposed in this paper.In this paper,the main equation of compressive strength prediction for concrete is given.The test data of the same kind of concrete is used to establish a fitting function model.The related fitting function and the main equation together form the Energy prediction relationship.The analysis and calculation results for normal concrete,high strength concrete and recycled aggregate concrete show that the theoretical confined compressive strength is in good agreement with the test results.The energy description relationship proposed in this paper has good theoretical prediction ability.