Behaviour of GFRP Reinforced and GFRP Encased Square Concrete Members under Different Loading Conditions

The use of reinforcement with fibre reinforced polymer (FRP) composite materials have emerged as one of the alternatives to steel reinforcement for concrete structures prone to corrosion issues (ACI 440.1R–15 2015). However, the mechanical behaviour of FRP reinforcement is different from that of steel reinforcement. In general FRP bars have a higher strength-to-weight ratio, but lower modulus of elasticity as compared to steel. Furthermore, when subjected to tension, FRP bars do not experience any plastic behaviour before rupture. Also, the compressive strengths of FRP bars are relatively low compared to the tensile strengths and are subjected to significant variations. Therefore, due to the differences in properties, GFRP bars cannot simply replace steel bars (ISIS 2007). The level of understanding of the behaviour of FRP reinforced compression members has not reached a level where design standards are available for such members. Having said this, the current ACI 440.1R – 15 (2015) design guideline recommends neglecting the compressive contribution of FRP reinforcement when used as reinforcement in columns, in compression members, or as compression reinforcement in flexural members. Most of the findings of studies investigating FRP reinforced concrete columns have been reported based on testing under concentric loading with the behaviour of such members under eccentric axial loads not sufficiently addressed in the previous studies.