BEHAVIOUR OF CONCRETE FILLED SATAINLESS STEEL COLUMN UNDER AXIAL COMPRESSIVE LOAD

Abstract

Concrete filled stainless steel tubular columns (CFSST) is an improved and innovative version of composite structure due to better mechanical properties compared to mild steel such as higher strength and ductility, corrosion resistance, fire resistance, speedy construction and low maintenance cost. It exhibits a rounded stress-strain behaviour with significant strain hardening. This study presents experimental as well as extensive numerical investigations on concrete filled stainless steel tubular (CFSST columns under concentric and eccentric axial loads. The experimental program conducted with twenty-four (24) CFSST columns. Out of those eighteen (18) concretes filled and six (6) hollow columns were constructed with various size, shape and concrete strength. These CFSST columns were tested for concentrically applied axial loads to observe the failure behaviour, the ultimate load carrying capacity and axial deformation. Numerical simulations were conducted on CFSST columns under axial compression using finite element method. Both geometric and material nonlinearities were included in the FE model. A concrete damage plasticity model was used to simulate the concrete material behaviour. Static general solution strategy was implemented to trace a peak and post peak response of CFSST columns under various conditions of loading. To validate the model, simulations were conducted with exactly same geometric and mechanical properties of current experimental study and test specimens from published literatures. Comparisons were also made between the FE predictions and experimental results in terms of peak load and corresponding strain, load versus deformation curves and failure modes of the CFSST columns. In general, the FE model was able to predict the strength and load versus displacement behaviour of CFSST columns with the accuracy of 95 percent. A parametric study was conducted using the numerical model to investigate the influences of geometric and mechanical properties of CFSST columns subjected to axial compression. The geometric variables were load eccentricity ratio (e/D), construction stainless steel ratio (D/t) and slenderness ratio (L/D) to generate more results to investigate the behaviour of CFSST columns. The concrete strength was varied from normal (30 MPa) to ultra-high strength (120 MPa) and steel strength 448 MPa to 707 MPa. In general, e/D ratio, D/t ratio, L/D ratio, strength of steel and concrete was found to greatly influence the overall carrying capacity and ductility of CFSST columns. The effects of ultra-high strength concrete (120 MPa) and high strength stainless steel of 707 MPa on column behaviour was also explored. The Numerical results are also compared with the code predicted capacities (AISC-LRFD 2010). Finally, on the basis of the parametric study a prediction co-relation P0 = Asσ0.2 + (D/t)-0.014 Acfc. has been proposed to determine the sectional capacity with 98 percent accuracy for CFSST square columns.