Manitoba has a large number of timber bridges that will be in need of rehabilitation or replacement in the near future. The estimated cost of replacement was projected at more than ;An experimental program was conducted at the University of Manitoba to test salvaged timber stringers, strengthened with GFRP laminates. A total of twenty six 130 x 330 x 4500 mm creosote- treated Douglas-Fir samples were tested in three point bending. Three groupings were investigated to study the effect of reinforcement on the increase of the stiffness of the beams. The first group consisted of 10 samples with GFRP laminates placed on the tension side only (Group T), while the second group of 10 samples were reinforced with GFRP laminates alongside both tension and compression zones (Group TC). The third group consisted of 6 samples post-tensioned with hardwire on the tension side and GFRP sheets at an angle of 45° in the shear zone (Group P).;This study found that the strengthening with GFRP laminates increased the strength and the stiffness of the beams by on average by 36% and 3% for Group T and by 31% and 3.5% for Group TC, respectively. It was also found that strengthening with the post-tensioned hardwire sheets increased the stiffness of the third group of tested beams by an average of 4%.;It was found that there is no significant increase in the stiffness of the beams reinforced with GFRP laminates, primarily because of the number and quality of the samples. All beams used in this program were salvaged beams that originated from a 60 years old bridge. Therefore, these stringers had developed defect, such as splits and checks that deteriorated their original grade. With samples of this variability, it was important to increase the number of beams for statistical analysis. Therefore a database of FRP strengthened timber beams tested by other researchers was assembled to facilitate further study on the effect of FRP on the behavior of timber.;During previous decades, many studies were performed on strengthening timber beams with fiber-reinforced polymers (FRP). This material is non-corroding, has high modulus of elasticity and strength, very low weight and, therefore, is an excellent choice for rehabilitation projects. This research will focus on the use of glass-fibre-reinforced polymer (GFRP) laminate for strengthening of existing aged timber stringers.;Analysis showed that overall there was no significant effect of strengthening on stiffness of the beams. Shorter span beams (up to 5 m length) showed some increase in stiffness with increasing the reinforcement ratio, however longer beams (10 m) showed no effect of strengthening on beam stiffness with increasing the reinforcement ratio. This result supports the current CSA S6-06 (2006) provisions that do not advocate for stiffness increase when their strengthening method is used.
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