Multiple anchorage zones in fibre-reinforced polymer prestressed concrete structures

Corrosion in conventional steel-reinforced and prestressed concrete structures is a major durability concern within the construction industry. Fibre-reinforced polymer (FRP) materials have received widespread interest as an alternative material to steel. Due to the low stiffness of these materials in comparison with steel, it could be argued that concrete structures containing FRP should be prestressed. In doing so, this removes much of the strain capacity in the FRP so that serviceability of the structure is ensured and efficient use is made of all materials. Although relevant research into FRP-prestressed concrete is well established, the area of anchorage zones has received very little attention. The current research concentrates on the behaviour of post-tensioned anchorage zones subject to multiple anchors, with the feasibility of adopting FRP bars as equilibrium reinforcement. Over 56 anchorage zone specimens have been tested, subject to multiple loads under a strip-loading condition. Specimens were loaded vertically through square bearing plates to represent post-tensioning action, and both aramid- and carbon-fibre-reinforced polymer (AFRP and CFRP respectively) bars were used as reinforcement. Test results have been compared with predictions based on an existing design approach that has been modified for the case of FRP reinforcement. It has been found that the existing design approach is overly-conservative when low percentages of FRP reinforcement are adopted and appears to become unsafe when high percentages of FRP reinforcement are present within the specimens. Furthermore, it has been found that such FRP reinforcement generally has less of an influence on the ultimate load capacity than might have been expected at the outset. However it provides both crack growth resistance and integrity of the anchorage zone. Moreover the distance between the loading plates has a major influence on the cracking and ultimate load behaviour of anchorage zones.