MINIMUM REINFORCEMENT RATIO FOR TIMBER BEAMS REINFORCED WITH GFRP

摘要

An experimental program was conducted at the University of Manitoba to investigate the flexural strength of timber beams reinforced with glass-fibre reinforced polymer (GFRP) bars and determine whether the minimum reinforcement ratio of 0.2% specified in the CAN/CSA-S6-06 (2006) could be reduced. This ratio was specified in the code to ensure that the strength of the timber beams will be increased in flexure by at least 20% due to FRP bars crossing the existing defects in the timber beam. Fifty-eight untreated Douglas-fir timber beams with dimensions of 75x250x2400 mm were tested in three point bending till failure. The grade of all the beams was uniformly reduced to No. 3 by introducing artificial defects (38mm diameter holes) into the beams using a statistically random process. Of the 58 beams, 18 were control beams, 20 were strengthened with 1-5mm diameter GFRP rod, and 20 were strengthened with 2-5mm diameter GFRP rods. Shear reinforcement was used with some success to prevent shear failure of the samples that tend to dry out and develop splits before testing. The results showed that the minimum reinforcement ratio outlined in the CAN/CSA-S6-06 can be reduced from p = 0.2% to p = 0.1% without a significant change in bending strength. The control and strengthened beams carried an average load of 39.2kN and 51.9kN respectively with a strength increase of 24.5%. The minimum failure load increased from 20.6kN to 36.0kN, a 42.8% increase, demonstrating the ability of the GFRP to effectively increase the beam strength for the lower strength beams.