Experimental Study On Dynamic Mechanical Properties Of Concretefilled Double Steel Tube Under Impact Loading

With the increase of vehicle colliding with piers,ship colliding with piers,terrorist bombings and accidental explosions,the possibility of bridges and other engineering structures subjected to impact and blast loads is increasing,more and more scholars focus on dynamic mechanical properties of engineering materials and the structure under impulsive loading.The existing researches show that the concrete filled double skin steel tube(CFDST)has good mechanical properties under quasi-static loading,but the research on its dynamic characteristics is relatively few,this paper uses the combined method of experimental research,numerical analysis and theoretical analysis on the dynamic mechanical properties of CFDST,the main work is as follows:(1)The impact tests of CFDST were conducted with a diameter of 75 mm Split Hopkinson Pressure Bar(SHPB)experimental apparatus,study the influence of the different impact velocities and different specimen parameters on the strain rate effect and related mechanical properties of CFDST.(2)Set up a numerical model of concrete filled double skin steel tube SHPB tests to simulate the impact of concrete filled double skin steel tube,the influence of the steel ratio,steel strength,concrete strength,hollow ratio on the dynamic mechanical performance of CFDST were researched.(3)The dynamic stress-strain relationship of concrete,concrete confined with steel tube and concrete filled steel tube are studied respectively to provide a basis for establishing a dynamic constitutive model that facilitates engineering applicationsThe main conclusions are as follows:(1)The SHPB experimental study shows that: the critical strain rate and the sensitivity of strain rate of CFDST is lower than concrete,but has good plastic deformation capacity,energy dissipation capacity and multiple impact resistance;within strain rate range in this paper,the dynamic restraining force of outer steel pipe to sandwich concrete increases with the increase of strain rate;the dynamic amplification coefficient calculation formula of CFDST presented in this article can reflect the dynamic enhancement of dynamic compressive strength of CFDST under impact loading.(2)The numerical simulation study of the SHPB test of concrete filled double skin steel tube can reflect dynamic characteristics of CFDST under impact load.Parametric study analysis shows that the parameters such as the thickness and strength of the outer steel tube,the strength of the core concrete and the hollow ratio of the specimen have great influence on the dynamic characteristics of the CFDST.With the continuous increase of impact velocity,the confinement effect of steel pipe on concrete becomes more obvious,and the dynamic binding force of concrete pipe to concrete increases with the increase of strain rate.(3)The dynamic stress-strain relationship of concrete confined with steel tube,concrete filled steel tube and concrete filled double skin steel were presented in this article,which are agreement with the experimental results or numerical simulation results and it can reflect the basic mechanical behavior of concrete and steel tube under impact loading.It shows that the dynamic stress-strain relationship established in this paper can provide a reference for engineering design and analysis.