An Experimental study on behavior of circular reinforced concrete columns enclosed GRP casing and FRP sheets

Nowadays, strengthening of column by using fiber reinforced polymer (FRP) composites is considered as the strengthening technique of these loading elements in a structure. In this technique, increasing the surrounding pressure on radial levels of the concrete column increases the compressive and tensile strengths of the concrete element, reduces slenderness, and increases the buckle load and ductility of this element. Moreover using glass-fiber reinforced plastic pipes (GRP) as the concrete column casing in addition to the independence of the need for framing leads to confinement effect on the concrete, high ductility and energy absorption, reduction in shrinkage and creep of concrete, lack of contact of the concrete with the corrosive factors, high construction speed, and proper loading capacity. In this research, compressive capacity test was conducted on 6 cylinder reinforced concrete columns (RCC) of 150 mm and diameter 600 mm height, with and without GRP casing, and the effect of FRP wrapping was studied on them as the confining factor. The research results showed that using FRP wrapping and GRP casing improves the compressive capacity and ductility of RCC. Adding one or two FRP wrapping layers increased the compressive capacity by 18.5% and 26.5% on the average, while using GRP casing increases the compressive capacity up to 300% on the average and this shows that although FRP wrapping and GRP casing are both confined, GRP casing is more effective in increasing the compressive capacity due to its higher confinement and similar ductility with RCC.