Discussion of Fiber-Reinforced Polymer Strengthening of Concrete Bridges That Remain Open to Traffic

This brief discussion article comments on a study of traffic loads applied to a reinforced concrete bridge during and after its strengthening with externally bonded fiber-reinforced polymer (FRP) reinforcement (W. Reed et al, 2005). The study included eight beams: seven of them were strengthened with a precured, unidirectional, carbon-fiber laminate strip that represented the materials used on an actual bridge. The variables tested included the intensity and frequency of load cycles applied during the epoxy-curing period, the thickness of the epoxy layer, and the thickness of the FRP strip. The study showed that for all of the traffic loads applied during and after installation no reduction in strengthening was seen. The experiment concluded that concrete bridges can be strengthened effectively even if they remain open to traffic during the procedure. In this commentary, Barnes reminds readers of the importance of considering the effects of traffic vibration during curing. Traffic vibration would have an effect on the strength of the adhesives typically used for this application. However, as the failure plane in an FRP strengthened concrete beam is typically within the concrete, the weakening of the adhesive does not affect the overall load capacity of the strengthened beams. Barnes concludes by cautioning that in other situations, such as steel beams, vibration from traffic loads may indeed lead to a reduction in ultimate capacity of the strengthened member.