Flexural Strength of Posttensioned Timber Beams

An experimental program was conducted at the University of Manitoba to test salvaged timber stringers posttensioned with external carbon fiber–reinforced polymer (CFRP) bars or steel guy cables. A total of 22 creosote-treated Douglas-fir beams with dimensions of 130×330×4,500 mm were tested in three-point bending. Six beams out of the 22 were control beams without any reinforcement. The remaining 16 beams were posttensioned using different reinforcement configurations. Four beams were posttensioned with draped CFRP tendons (Group CD), four beams were posttensioned with straight CFRP tendons (Group C), four beams were posttensioned with draped steel cable (Group SD), and four beams were posttensioned with straight steel cable (Group S). The experimental results found that the strength and the stiffness for Group CD were increased on average by 70% and 10%, respectively, while the strength for Group C was increased on average by 56% and showed no significant increase in stiffness. In contrast, the strength and the stiffness for Group SD were increased on average by 45% and 4%, respectively, while the strength for Group S was increased on average by 49% and showed no significant increase in stiffness.