Investigation and comparison of capacity and ductility of elliptical RCC's with GRP casing and CFRP wrapping under pure axial load

Bridges are behaviorally special compared to conventional structures. The uncertainty of bridges is much less than that of buildings, so the failure of columns in a bridge can lead to complete failure. The use of fiber reinforced polymer (FRP) composites into wrapping as one of the methods of strengthening of reinforced concrete columns (RCCs) of bridges has received much attention in recent years. High stiffness and characteristic strength, long life, corrosion resistance and controllable thermal properties are important advantages of FRP over conventional materials. The use of glass-fiber reinforced plastic pipes (GRP) as casing for bridge piers, removes molds, reduces costs, increases energy absorption and ductility, and reduces water-washing around bridge piers. In this study, compressive strength tests were performed on six samples of oval RCCs with diameters of 200 and 120 and height of 600 mm with and without casings and the effect of carbon-FRP on them as an enclosing was investigated. The results showed that the wrapping and casing increases the strength and ductility of the columns. Addition of one-layer and two-layer wrapping averagely increased the strength by 19.7% and 28.7%, respectively; while the use of casing resulted in a 4.15-fold increase in the strength. Although the wrapping and the casing both create the enclosure, the casing has a much greater effect on increasing the strength and ductility of the columns due to its greater enclosure. Comparison of wrapping enclosure with casing in the final axial deformation of these columns showed that the casing is much more effective.