Study On Axial Compression Performance Of Steel Tubular Engineered Cementitious Composite Column

As a new type of steel-concrete composite structure independently developed in China,concrete-filled steel tube composite column（CFSTCC）has obvious advantages of high bearing capacity,convenient construction and good ductility.In recent decades,CFSTCC has been widely used in high-rise structures,huge bridge structures and super high-rise structures,and has achieved good social and economic benefits.However,in real engineering practice,it was found that there are significant differences on the mechanical properties of the outer layer of CFSTCC which is made of steel reinforced concrete and the core of the concrete filled steel tube,the two have poor synergistic deformation ability,which resulted in the reduction of the durability of the CFSTCC,affecting the bearing capacity of the CFSTCC,and consequently limiting its development prospect in engineering practices.Engineered Cementitious Composites（ECC）is a kind of fiber reinforced engineering cement-based composite material with high ductility and strain hardening characteristics.It has similar compressive strength to concrete material.Under uniaxial load,the corresponding strain under the peak stress of ECC is about 2 times that of concrete,and its ultimate tensile strain can reach 3%-5%.By using ECC instead of ordinary concrete,it can effectively improve the brittle cracking issue of the outer layer steel reinforce concrete and the poor combination effect of composite columns,and subsequently improving the bearing capacity and durability of the component.Owing to that,in this paper,ECC is used to replace ordinary concrete to form steel tube-fiber reinforced engineered cementitious composite column,referred to as steel tube-ECC composite column.Experimental study and finite element numerical simulations were conducted in this paper to investigate the axial compressive properties of steel tube-ECC composite column.The main works of this study are as follows:（1）Eight steel tube-ECC composite columns were designed and fabricated which include four E-E series specimens,three C-E series specimens and one E-C specimen,and the axial compression test of the composite columns were completed.The failure pattern,load-deformation curve,ductility coefficient and peak load of the specimens were studied under different parameters,such as the yield strength of the steel tubes,the thickness of the steel tubes and the material of the inner and outer layers of the steel tubes.The experimental results show that the steel tube ECC composite column has better bearing capacity and ductility,E-E series and C-E series specimens mainly show ductile shear failure,and E-C series specimens show brittle material failure.（2）Numerical models were established using ABAQUS finite element software to simulate the loading process of steel tube-ECC composite column under uniaxial load.At first,the finite element results were compared with the experimental test results to verify the rationality of the model,and then based on this reliable simulation basis,the failure mechanism of the steel tube-ECC composite column under axial load was studied,and the influence of different parameters on its axial compression performance is discussed.Research shows that the yield strength of steel pipe,steel pipe thickness,and core material strength has a greater impact on the axial compression performance of composite columns.Increasing the thickness of the steel pipe and the yield strength of the steel pipe will significantly increase the bearing capacity and initial stiffness of the specimen;increasing the ECC strength and the strength of the core concrete will significantly increase the bearing capacity and ductility of the specimen;increasing the diameter of the longitudinal reinforcement and the spacing of the dense stirrups has limited influence on the bearing capacity increment on the specimen;and among the two,the density of the stirrup spacing has a greater impact on the ductility of the specimen.