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Thin Walled Cold-Formed Concrete Filled Tubular Square Column are manufactured by flare welding at center of column width for cold formed L shape plates of 4 piece and improved composite effect of concrete and steel by vertical inner anchor. Also, Axial resistance of concrete is increased by confine effect of steel tube and steel prevent local buckling of steel column. In this study, we introduced manufacture method of thin walled cold-formed square column steel square concrete filled tubular column and structural performance of the welded built-up square stub column was verified by structural test for ten specimens with parameters of concrete strength, type of steel tube, width to thickness ratio of steel tube.

H-beams set up between columns are widely used to support building slabs. However, H-beams have fixed joints and the bending moment at both ends of the beam under uniformly distributed load is twice as great as the moment at its center. Because beam design is based on ultimate moment, its depth gets to be larger, which leads to the problem of smaller available space on each floor. If the ends of H-beam which are vulnerable to ultimate bending moment are additionally reinforced, beam design based on the bending moment at beam center is feasible. In this study, 4 specimens were fabricated for structural experiment with variables of the purpose of end-reinforcing steel plates, bar reinforcement and load transfer method in order to analyze the structural performance of end-reinforced steel frame beams (hereinafter Eco-girder system).

Concrete-filled steel tube structure has advantages such as excellent deformation capacity, energy absorption and fireresistance. However, CFT column has the drawback of local buckling at steel tube due to the deterioration of confinement effect after steel tube yield. To solve the problem, CFT column system reinforced by CFRP(Carbon Fiber Sheets) will be introduced and the structural behaviors of CFRP reinforced columns will be compared with those of the current CFT columns. The main experimental parameters are diameter-thickness (D/t) and number of carbon FRP sheet layers. 10 specimens were prepared with the main experimental parameters. Axial compression test were conducted and axial behavior maximum strength capacity, and ductility capacity were analyzed between CFRP reinforced columns and the current CFT columns. To propose of design formula for FRP reinforced CFT columns, confinement effectiveness coefficient of confined concrete were proposed based on the experimental results. Finally, base on the coefficient, the axial design formula for FRP reinforced CFT columns were proposed and compared the design strength values with the experimental strength values.