Behavior of structural members produced thin walled cold formed steel tubular sections(CFST)under axial compression (experimental & analytical)

In the structural members tension and compression stresses occur at different regions according to the loads and load conditions. Since 1850s it can be seen that optimum resisting section against these stresses at the same member is the reinforced concrete which has a composite structure. But recent studies about concrete filled steel tubes (CFST) become important in the structural engineering area. This system provides quick construction without removing formwork. Steel member prevents the lateral expansion of concrete as done by stirrups. Steel tube performs both longitudinal and lateral reinforcement as well as is it used as formwork. Concrete core resists axial force, at the same time it prevents buckling of steel to the inside direction of the tube.In this study compression of concrete, modulus of elasticity, steel coupon and friction tests are performed in order to determine the material properties. Sixty four concrete filled steel tube specimens are used for axial compression tests. Effect of width/thickness (b/t) ratio, compressive strength of concrete and geometrical shape of cross section parameters on axial bearing capacity, ultimate load, strain, ductility and buckling are investigated. Within this purpose 18.75, 30.00, 50.00, 100.00 b/t ratio values; 10, 20, 30 MPa concrete compressive strength values and circular, hexagonal, rectangular and square shaped cross sections are chosen.Analytical models of specimens are developed using finite element program (ABAQUS) and the results are compared and presented. The presenting of solutions in terms of both economical and engineering point of view, design procedure can be expected that results provide an innovative perspective for using of steel and concrete together as a composite material.