NUMERICAL INVESTIGATION OF THE SHAPE EFFECT ON ECCENTRICALLY LOADED CONCRETE FILLED STEEL TUBE (CFST) COLUMNS

Abstract

The concrete filled steel tube (CFST) column as a composite structure can enhance the structural behavior of both components, the confinement of the core concrete by steel tube improves the load carrying capacities and ductility of the CFST columns and the concrete infill can enhance the effective stiffness of the steel tube and decrease the risks of global and local buckling. The main objectives of this research is to investigate the confinement effect on the three cross- sectional shapes such as circular, square and rectangular CFST columns and the effect of using UHPC on CFST column to improve its capacity. Numerical analysis is done via ABAQUS software to examine the axial load deformation behavior for three different shapes of the CFST members. A total of Fifty-seven (57) CFST column for the three cross- sectional shapes are modeled to investigate four parameters, such as the eccentricity distance of 0mm, 20mm, 40mm and 50mm, the steel tube yield strength of 275MPa, 355MPa and 420MPa, the core concrete compressive strength of 30MPa, 60MPa, 90MPa and 125MPa and the column length of 1000mm, 1600mm and 2000mm to investigate the confinement effect on three cross-sectional shapes. As inferred from the FEA output results the increase of the eccentricity distance from 0mm to 20mm, 40mm and 50mm results in the decrease of the ultimate load bearing capacity by 36.5%, 54.94% and 60.384% for circular, 37.65%, 55.2% and 60.44% for square and 45.462%, 61.56% and 66.46% for rectangular CFST column respectively. Increasing of the steel tube yield strength from 275MPa to 355MPa and 420MPa increases by 7.01% and 11.56% for circular, 5.96% and 10.8% for square and 6.9% and 11.76% for rectangular sections respectively. The increasing of the core concrete compressive strength from 30MPa to 60MPa, 90MPa and 125MPa results in the improvement by 24.78%, 45.72% and 53% for circular, 26.95%, 46.97% and 55.954% for square and 23.79%, 40.74% and 47.82% for rectangular CFST column respectively and the increase of the column length from 1000mm to 1600mm and 2000mm reduce by 17.5% and 26.9% for circular, 14.16% and 25.39% for square and 20.04% and 33.9% for rectangular sections respectively.