Experimental Study On The Effect Of Age And Strength Grade On Energy Storage And Dissipation Characteristics Of Concrete

The concrete destruction process is accompanied by energy input,storage and dissipation.It is of great significance to study the failure mechanism of concrete from the perspective of energy.In order to explore the energy evolution and storage and consumption characteristics of concrete at different ages and strength grades,this study carried out uniaxial compression and single-cyclic loading-unloading uniaxial compression tests on C35 concrete specimens at 3,7,15 and 28 days.Five concrete specimens were subjected to single-cyclic loadingunloading uniaxial compression tests at five preset unloading stress levels(0.1,0.3,0.5,0.7,and 0.9 of ultimate strength)at each age.The uniaxial compression cycle loading and unloading test was carried out on C20,C30 and C40 concrete by means of equal displacement loading.According to the envelope of the stress-strain curve,the input strain energy,elastic strain energy and dissipated strain energy at the unloading point are calculated,and then the energy evolution and storage and consumption characteristics are investigated.The main conclusions are presented as follows:(1)During the 28-day age,the input strain energy,elastic strain energy and dissipated strain energy increased nonlinearly with the increase of the actual unloading stress level in the pre-peak loading stage,and the growth law can be well fitted by using the quadratic function or the power function.At different ages,as the actual unloading stress level increases,the elastic strain energy and dissipated strain energy increase linearly with the input strain energy,that is,the elastic strain energy and dissipated strain energy are proportional to the input strain energy.On this basis,the compression energy storage coefficient and dissipation coefficient of concrete are proposed.During the 28-day age,the compression energy storage coefficient increases linearly with age.(2)During the whole loading process,the dissipated strain energy and input strain energy are positively proportional to the function,and the proportion of dissipated strain energy is more than 90%;the elastic strain energy and input strain energy have a two-stage linear relationship: first linear increase,and then linear decrease.(3)In the pre-peak loading stage,the compression energy storage coefficient of the same strength grade is close;under different strength grades,the compression energy storage coefficient of concrete increases with the increase of strength grade.The larger the compression energy storage coefficient,the stronger the ability to characterize the energy stored in concrete.Different strength grades of concrete,the higher the strength grade,the denser the internal structure at the age of 28 days,the fewer defects,and the higher the compression energy storage coefficient.(4)Based on the linear energy storage and dissipated laws,the elastic strain energy and dissipated strain energy at the peak point were calculated.The dissipated strain energy is calculated by using the linear energy dissipation law,and the ratio of the dissipated strain energy to the concrete constitutive energy is defined as the damage variable,and the relationship curve between the damage variable and the concrete strain is obtained.Based on the traditional constitutive equation,the concrete damage constitutive equation based on the linear energy dissipation law is established.