Axial loading tests on short and long hollow structural steel columns retrofitted using carbon fibre reinforced polymers

This paper describes the behaviour of axially loaded short and long square hollow structural section (HSS) columns, strengthened with carbon fibre reinforced polymer (CFRP) sheets. Twenty-seven short-column and five long-column HSS specimens were tested. The effect of CFRP sheet orientation in the longitudinal and transverse directions was studied for short columns. For long columns, CFRP sheets were oriented in the longitudinal direction only. A maximum strength gain of 18% was achieved for short columns with two transverse CFRP layers. For long columns, the maximum strength gain of 23% was achieved with three longitudinal CFRP layers applied on four sides. In all CFRP-strengthened long columns, lateral deflections were reduced. Strength gain in long columns was highly dependent on the column's imperfection. As such, no correlation was established between strength gain and number of CFRP layers. CAN/CSA 16-01 equation was modified to account for CFRP through transformed section analysis so that they could be used to predict the axial-load capacity of long columns.Key words: retrofit, steel, HSS, column, FRP, carbon, buckling, strength, stiffness.