PERFORMANCE OF CIRCULAR CONCRETE FILLED STEEL TUBE SHORT COLUMNS UNDER AXIAL COMPRESSION

Abstract

This thesis aims at developing a suitable constitutive model addressing the behavior of short Concrete Filled Steel Tubular column on the compressive response under axial loads. Ultimate load carrying capacities obtained by, Schnider (1998) and Huang et al (2002), using experiments have been compared with the analytical model values. The nonlinear finite element program ABAQUS 6.14-2 is used to study the force transfer between steel tube and concrete core. The interaction between steel tube and concrete core is modeled using surface-to-surface contact, a clamped end boundary condition is used (fixed at the bottom and allowing movement in the loading direction at the top) and a displacement controlled loading is applied. The analytical results validated with experimental data extracted from experiments by the Authors in terms of axial load vs. axial deformation graphs. Then a parametric study is conducted using twenty seven circular CFST columns to investigate the load carrying capacities and confinement of CFST columns. Here, the main parameters are the yield stress of steel, diameter of the column and thickness of the steel tube. 120-137% of load carrying increment is shown for concrete filled steel tubes by addition of concrein the hollow steel tube. And also 95% of load increment by changing the diameter of the column and keeping other parameters constant. 8-16% of load increment is recorded by changing the steel yield strength and keeping other parameters constant. And also a maximum 5.27% increase of load carrying capacity is observed by changing L/D from 3 to 5 and a decrease in the load carrying capacity is observed with an increase of L/D ratios from 5 to 7. A comparison of ultimate failure loads from nonlinear finite element program ABAQUS 6.14-2 with the predicted failure load from Euro code Part-4 (EC-4), ACI-318 (2005) (American Concrete Institute), for axially loaded columns will be carried out in this research study. A difference in increase of 7% is calculated using EC-4 and a difference in decrease of 33% is calculated using ACI-318 with comparison to the modeled data.