Application of Fiber Reinforced Plastic (FRP) in the construction industry is desired due to its advanced properties such as high resistance to corrosion, high tensile strength and low density. Many researchers have conducted various investigations on application of FRP for retrofitting, reinforcing and prestressing of concrete structures. As tendons work at high stress levels, fatigue will be a detrimental factor influencing their performance. This project was aimed at investigating the fatigue behavior of Glass Fiber Reinforced Plastic (GFRP) tendon prestressed concrete beams....[ Read more ]

Application of Fiber Reinforced Plastic (FRP) in the construction industry is desired due to its advanced properties such as high resistance to corrosion, high tensile strength and low density. Many researchers have conducted various investigations on application of FRP for retrofitting, reinforcing and prestressing of concrete structures. As tendons work at high stress levels, fatigue will be a detrimental factor influencing their performance. This project was aimed at investigating the fatigue behavior of Glass Fiber Reinforced Plastic (GFRP) tendon prestressed concrete beams.

The research included three parts, bond strength, prestress loss and fatigue behavior of prestressed beams. In the first part, the bonding properties between GFRP tendon and concrete were studied. Circular specimens with GFRP rods embedded in center of cement mortar discs were prepared and tested to determine the bond performance of GFRP tendon. The second part was to study the prestress loss of GFRP when used as prestressing tendon. It is generally assumed that prestress loss of GFRP tendon would be smaller than that of steel due to its lower stiffness. Beams with GFRP rod as prestress tendon were made and tested to verify this assumption. The last part was to investigate the fatigue behavior of GFRP tendon prestressed beams by comparing with steel tendon prestressed beams. Beams prestressed by GFRP tendon and steel tendon were prepared and tested at various loading levels for comparison.

Test results showed that surface condition has great influence on bond strength while mortar composition only has limited effect. Comparing with smooth surface steel rod, smooth surface GFRP rod possessed slightly smaller bond strength. While sand blasted rough surface GFRP had great improvement for about 100% increase in bond strength. However, reinforcement was required to be added in the rough surface GFRP specimens to prevent the formation of radial cracks during the push-out test.

Two beams prestressed with rough surface GFRP tendon and smooth surface steel tendon respectively were monitored for prestress loss. The results showed that the rough surface GFRP tendon had a slightly higher strain loss than the smooth surface steel tendon. However, with a much lower Young’s modulus, in the scale of about one fourth of the steel tendon, the rough surface GFRP tendon had only about one fourth of prestress loss of steel tendon.

Fatigue behaviors of GFRP tendon and steel tendon prestressed beams are similar, especially in lower loading levels. Fatigue tests showed that the GFRP tendon prestressed beams had a lower fatigue strength than steel tendon prestressed beams. The GFRP tendon and steel tendon prestressed beams failed quickly when loaded at 60% and 80% of their ultimate strength respectively. All prestressed beams loaded with maximum cyclic load not exceeding more than 10% of their predicted cracking loads had fatigue life more than two million cycles.