Research On Impact Resistance Design Methods Of Circular Concrete Filled Double-skin Steel Tubular

Circular concrete filled double-skin steel tubular（CFDST）is a kind of steel-concrete composite component formed by pouring concrete between concentric placed inner and outer steel tubes.It has the advantages of large load bearing capacity and bending stiffness,cross-section development,light weight,good ductility and convenient construction,which can be widely used in building,bridge and underground engineering.Impact is an inevitable accidental load during the life cycle,which may lead to damage or even loss of bearing capacity of the structural members.Therefore,it is essential to quickly evaluate the damage degree of components under impact.In this paper,ABAQUS finite element model is used to analyze the mechanical properties of circular CFDST members under the coupling action of axial force and impact.The dynamic displacement response of the member was calculated based on the equivalent single-degree-of-freedom method.The research contents are as follows:（1）The refined finite element model of CFDST members under the coupling action of axial force and impact was established,in which the strain rate effect and interface contact between steel and concrete were considered.The axial force is applied by coupling the static implicit analysis and dynamic explicit analysis in sequence.Based on the test data,the reliability of the finite element model was verified.（2）Based on the verification model,the working mechanism of circular CFDST members under the coupling action of axial force and impact load was analyzed,including the whole process of impact,failure mode,interaction between steel tube and concrete,energy dissipation capacity,etc.Effects of axial load ratio,nominal section steel ratio,hollow ratio,section diameter,material strength,impact velocity and impact mass on the impact resistance of components were studied.The calculation formula for the impact resistance bearing capacity of members was developed.（3）The equivalent single-degree-of-freedom（SDOF）system of circular CFDST members subjected to impact in the mid-span under axial compression was established.Based on the finite difference method,the calculation method of displacement-time history of circular CFDST members was given.The accuracy of the equivalent single-degree-of-freedom method was verified by the results of typical experiments and finite element models.