Investigation on the behaviour of reinforced concrete columns made of high-strength concrete, enclosed with GRP casing and CFRP sheets

This paper presents the results of an axial pressure test on reinforced concrete columns made of high-strength concrete, which are encapsulated using a glass-fiber reinforced plastic pipes (GRP) and also with fiber reinforced polymer (FRP). The purpose of this study was to investigate the load bearing behavior of concrete columns enclosed with GRP casings and CFRP composites under compressive loads. In this research, the effect of using the GRP casings, CFRP sheets, and also the number of CFRP layers has been investigated. In this research, six circular reinforced concrete columns were manufactured from high-strength concrete, half of columns (group 1) had a GRP casing and the other half (group 2) without casing. From each group, a column had no CFRP reinforcement layer, a column with one layer and another column with two layers of CFRP reinforcement. All columns were tested under concentrated compressive force. The results showed that the use of CFRP sheets and GRP casings improved the compressive strength and durability of the reinforced columns. The addition of a layer and two layers of CFRP increased an average of 10.2% and 24.8% in compressive strength, while the use of a GRP casing increased averagely 3.83 times in compressive strength of the columns. The results indicate that although the CFRP sheets and the GRP casings are both enclosed, the GRP casings, due to their greater enclosure, have a much greater effect on the compressive strength and the ductility of the reinforced concrete columns.