COMPOSITE COLUMN

COLD-FORMED STEEL-CONCRETE COMPOSITE COLUMNS:-

A new system of composite columns is developed using lipped cold-formed steel channels with embossments and cast-in-place concrete. The combined action of the embossments and the channel’s lips leads to very good bond between the steel and the concrete. It has been found that by replacing the standard longitudinal reinforcing bars by cold-formed steel sections of equal area, the structural performance of the columns remains almost unchanged, while considerable savings are achieved in time and material of construction. Hence in this study, an attempt is made to experimentally investigate the effect of stiffeners in the behaviour of cold-formed steel-concrete composite columns

ROLE OF STIFFENERS:-

The steel-concrete composite columns exhibit improved strength and ductility characteristics owing to the ability of the concrete infill to prevent the local buckling of the steel tube. Though concrete infill prevents inward local buckling, outward buckling still limits the sections from yielding. The provision of stiffeners is known to effectively delay the local buckling effects in the case of hollow cold-formed steel columns.

EXPERIMENT TO INVESTIGATE EFFECT OF STIFFENERS IN THE BEHAVIOUR OF COLD-FORMED STEEL-CONCRETE COMPOSITE COLUMNS:-

Incorporating cold-formed steel sections in composite columns creates further complications in connection as welding of very thin sections pose practical difficulties. Hence connection using self-tapping screws replaces the conventional connections in this work.

A series of 12 specimens were tested to determine the cross-sectional strength and the failure patterns. A scaled down cross section of 100 mm x 100 mm was chosen. Cold rolled steel of 1.6 mm was adopted. Columns belonging to different slenderness category namely short, intermediate and long column were selected. Sections with and without intermediate stiffeners in the form of bends were investigated. A 1000 kN hydraulic jack mounted on a column testing frame was used to apply the load. The support condition assumed was simply supported and it was achieved by the provision of two hinged plates on both sides of the column. The behavioural responses of the specimens were recorded by DAQ system with the help of linear variable displacement transducers (LVDT) for axial displacement and 300 kN load cell for the loads imposed.

CONCLUSION:-

The stiffener provided is found to be effective for all hollow sections, but their effectiveness is not pronounced in the composite sections. Self-tapping screws are found to provide a good mode of connection