Impact Resistance Of Pre-stressed Confined Concrete With Truncated Cone

The concrete-filled steel tube has superior impact resistance.In order to maximize the utilization of the steel tube at the elastic stage,pre-stressed confined concrete was designed and prepared,thereby completing the active confinement of the steel ferrule to the concrete before being loaded by the external force.In this paper,relevant experiments and numerical simulations were carried out,and the main research contents and conclusions are as follows:(1)Based on the new concept of pre-stressed concrete with truncated cone,the concrete specimens were prepared and tested by exploratory drop weight impact tests to investigate the effects of the form of confinement,the taper angle of the confinement ring,the difference between the confinement rings,the shape of the confinement ring and the concrete strength on the low-velocity impact resistance.The results show that:the presence of prestressing can substantially improve the low-velocity impact resistance of concrete;the low-velocity impact resistance of concrete is optimal when the taper angle of the confinement ring is 3°;within a certain range,increasing the thickness of the confinement ring is conducive to improving the confinement capacity,which in turn improves the low-velocity impact resistance of concrete;the impact resistance of specimens with hexagonal confinement ring is better than that of circular and quadrangular specimens;The wedge-tightened truncated cone form can more significantly improve the low-velocity impact resistance of high-strength concrete.(2)Based on the drop weight impact tests,the method of applying pre-stress was improved and pre-stress loading progress tests was carried out.The results showed that the pre-stress applied on the concrete increased with the increase of the concrete cone table body surplus.Except for specimen C1L(0.3),the confined ring strains of the remaining specimens showed an approximately linear distribution.When the circular and hexagonal specimens have the same cross-sectional area,the pre-stress value of the hexagonal specimen is smaller than that of the circular specimen,which is due to the stress concentration in the corners of the hexagonal specimen,which is not as continuous and uniform as that of the circular specimen.When the confinement ring is hexagonal,the specimen with smaller upper inner pair of edge distance provides greater pre-stress to the concrete,which is due to the further enhancement of the confinement effect of the confinement ring on the concrete cone.(3)LS-DYNA was used to carry out numerical simulation research,firstly,the numerical model is determined,and the prestressed concrete under different working conditions is simulated,and the simulated compression speed is selected as 1.0m/s and the grid size of the encrypted area in the center of the concrete cone is 0.5mm,which is more suitable;secondly,the simulated values obtained from the numerical simulation were compared with the experimental values and the agreement was good,thus verifying the reasonableness of the numerical model and algorithm.(4)Based on the determined numerical model,a numerical simulation study was carried out to analyze the effects of steel strength,concrete strength,steel content,confinement ring shape or the initial velocity of the projectile on the performance of concrete against high-speed projectile penetration.The results show that: with the increase of steel strength,the high-speed projectile penetration performance of the specimen increases,but when the steel strength exceeds 900 MPa,the high-speed projectile penetration performance of the specimen decreases when a pre-stress beyond a certain range is applied to the concrete cone;when concrete with strengths of 70 MPa and 97.5 MPa is used,the pre-stress beyond a certain range will cause the specimen to be penetrated by the projectile.When using concrete with a strength of 150 MPa,the specimen’s resistance to high-speed projectile penetration still has a tendency to improve;when the steel content of the specimen is 28%,its resistance to penetration is better than that of specimens with steel content of 9%,21%,and 39%,so a single increase in the steel content of the specimen to improve the specimen’s resistance to high-speed projectile penetration causes a waste of material performance;when the specimens use different shapes of confinement rings,the resistance to high-speed penetration by projectiles of circular specimens is better than that of specimens with hexagonal shapes of restraint rings.The higher the initial velocity of the projectile,the more obvious the improvement of the prestressing on the high-speed penetration performance of concrete.