Numerical analysis of behaviour of concrete beams with external FRP tendons

The use of FRP (fibre reinforced polymer) composites as external prestressing tendons is expected to be popular. A numerical investigation is conducted to evaluate the short-term behaviour of external FRP tendon beams, and the results are compared with those of external steel tendon beams. The analysis shows that beams prestressed with external CFRP and steel tendons exhibit similar behaviour, and that external GFRP tendon beams have lower flexural strengths but better ductility behaviour than do external steel tendon beams. The type of external tendons has no important effect on the redistribution of moments in continuous beams. The amount of prestressing reinforcement significantly affects the member behaviour, including cracking and ultimate loads, ductility, neutral axis depth and reinforcement stress. The crack pattern is greatly improved by providing a minimum amount of bonded reinforcement. The analysis also indicates that the ultimate load decreases linearly with increasing deviator spacing, provided that failure happens at midspan. A method for determining the optimum deviator spacing is proposed.