Long-term and fatigue behaviour of carbon fibre reinforced polymer prestressed concrete beams

Corrosion of steel reinforcement in civil engineering infrastructure is costing the North American economy billions of dollars annually in rehabilitation and replacement. The most severely affected structures are bridges and parking garages. In recent years, fibre reinforced polymer (FRP) reinforcements, developed for the aerospace industry, have been considered as a viable replacement for steel reinforcement in civil engineering infrastructure.; This thesis presents two separate experimental programs: one designed to examine the long-term behaviour of carbon FRP pretensioned concrete beams under sustained load conditions, and another to study the fatigue behaviour of unbonded carbon FRP post-tensioned concrete beams. The long-term test program consisted of three beams pretensioned with CFRP rods and one beam pretensioned with steel prestressing strand. The CFRP pretensioned beams had different prestress force levels, while the prestress force in the steel pretensioned beam was designed to be equal to that of one of the CFRP pretensioned beams to allow direct comparison. The experimental results show a satisfactory behaviour of CFRP prestressed beams compared to the steel pretensioned beam.; The fatigue test program consisted of a total of five unbonded post-tensioned concrete beams. Three of the beams were post-tensioned with CFRP rods while the remaining two beams were post-tensioned with conventional steel prestressing strands. The fatigue load limits were chosen to produce stress ranges of about 100 MPa in the lower prestressing reinforcement. During fatigue testing, prestressing reinforcements fractured at the prestressing rod-anchor junction. In the steel post-tensioned beam, fracture of wires of the prestressing strand resulted in redistribution of stress to the unbroken wires. In the CFRP post-tensioned beams, on the other hand, fracture led to splintering of the rod between the anchors and total loss of prestress force. The non-prestressed steel reinforcements fractured after about 54,000 fatigue cycles. No fracture of the GFRP non-prestressed reinforcement was observed during fatigue testing. This was attributed to the higher modulus of elasticity of steel reinforcement, which resulted in higher stress ranges during fatigue testing. The CFRP beams performed satisfactorily in fatigue as long as premature failure of the rods near the anchor could be prevented. (Abstract shortened by UMI.)...