Analysis of doubly loaded end blocks in FRP-prestressed concrete

Abstract

Corrosion in conventional steel-reinforced and prestressed concrete bridges is a major durability concern. Fibre-reinforced polymer (FRP) materials have received widespread interest as an alternative material to steel. Owing to the low stiffness of these materials compared with steel, it could be argued that concrete bridges containing FRP should be prestressed. In doing so, this removes much of the strain capacity in the FRP, so that serviceability of the bridge is ensured and efficient use is made of all materials. Although relevant research into FRP-prestressed concrete is well established, the area of post-tensioned anchorage zones has received very little attention. The current paper concentrates on the analysis (and the design) of post-tensioned anchorage zones subject to multiple anchors, with the feasibility of adopting FRP bars as equilibrium reinforcement. Using an elasticity-based model, both the position and load at first cracking have been predicted with good accuracy compared with the experimental results. Further, a plasticity-based model has been developed, in which equilibrium of the failing wedge formed underneath the bearing plates at ultimate load is considered, and which has also shown good correlation compared with test results. It is concluded that both the serviceability and ultimate limit state behaviours of post-tensioned FRP-reinforced anchorage zones subject to multiple anchors are predictable. The pre-cracking behaviour can be predicted using an elastic finite difference method, while a plasticity-based analytical solution can be used to predict the ultimate capacity.