Experimental Study Of Concrete Damage Under Complex Stress Paths

When the concrete structure is subjected to strong dynamic loads such as explosion or impact,the concrete will be in a very complicated and constantly changing stress state due to the propagation and reflection of stress waves in the concrete.Despite the prevalence of concrete applications,the understanding of the evolutionary behavior of damage under hydrostatic pressure is very limited.More and more researchers use numerical simulation to predict the response of building structures under blast loading.However,the existing concrete constitutive model only considers the damage of concrete under the action of partial stress,ignoring the influence of hydrostatic pressure on concrete materials.It is also believed that the concrete will not be damaged when it is unloaded before reaching the ultimate strength,that is,the strength of the material does not deteriorate under such a stress path.In view of the above research background,the concrete triaxial test is used to test the concrete damage of concrete under single and cyclic hydrostatic pressure paths and hydrostatic pressure and deviatoric stress.The main research contents include the following aspects:(1)The damage of concrete materials under hydrostatic pressure was studied.Cyclic hydrostatic load and single hydrostatic load were applied to a 50 mm cube specimen.The uniaxial residual strength test and ultrasonic flaw detection are performed on the loaded test piece.It is found that the damage degree of concrete under cyclic load is about 10% higher than that of single load.Aggregate-mortar interface transition zone(ITZ)is the most damaged area.Heterogeneity is the main reason that affects the damage of concrete under different stress paths.(2)The damage of concrete materials under confining pressure conditions was studied.The axial loading test under confining pressure was carried out,and it was found that the concrete specimen was unloaded before reaching the ultimate strength,and the uniaxial strength of the specimen was significantly degraded,that is,the inside of the concrete had been damaged.The damage of the internal microstructure of the concrete material was observed by scanning electron microscopy.It was found that the damage of the first principal stress direction was more serious than other directions.(3)The damage of concrete under proportional loading conditions was studied.A true triaxial test of concrete under different stress ratio loading paths was carried out.It was found that under the condition of proportional loading,the concrete was unloaded before reaching the ultimate strength,and the remaining uniaxial strength also deteriorated to varying degrees,and the damage to the concrete material was more serious than the hydrostatic pressure of the same grade.A concrete damage model considering the effects of partial stress damage and hydrostatic pressure damage is proposed,which serves as a reference for the improvement of concrete constitutive model.