Ultimate load of built-up cold formed steel column

Abstract

Cold formed steel (CFS) has been used as the primary structure for flexural and compression member due to varieties of advantages such as high strength to weight ratio, high corrosion resistance, and ease of fabrication. The criteria need to be considered in improving the structural strength is the fabrication method. Fast and easy fabrication can produce an efficient structure. Built-up of normal CFS into new member with higher strength can be produced efficiently by attaching the normal steel using self-drilling screw. CFS channel with constant size has been used to produce built-up, back to back (BTB), and box-up (BU) with varieties of length. The constant spacing were used at 400 mm centre to centre along its length and supported by using an angle plate that screw through its web. 18 nos of columns were tested for compression until the column cannot resist any increment of load. The ultimate loads were compared to the predicted buckling load using EC3-1-3. The prediction of column capacity is based on flexural buckling and torsional buckling failure. BTB column results in higher load except for 2.5 m length, while the differences of experimental load are up to 24 % to the experimental. Meanwhile, BU results in higher load for all columns with differences up to 80 % compared to the code and the code is considered too conservative for this column type.