Behavior of EBR FRP Strengthened Beams Exposed to Elevated Temperature

Abstract

Externally bonded laminates based on high strength fibers nowadays are often used to strengthen the structures. It is possible, that some of those strengthenings are subjected to direct insolation. The paper presents the dangers appearing with the rise of temperature caused by the infrared solar radiation. Heating conditions were planned on the basis of exposition of concrete samples during the summer months in the southern Poland. The maximum recorded temperatures in the adhesive layer reached 65°C and it was therefore 20°C higher than the glass transition temperature of commercially available adhesives based on epoxy resin. Laboratory tests included a group of fifteen reinforced concrete beams in the real scale, seven of them were strengthened with externally bonded CFRP strip, seven with SRP tape. They were tested in various temperature conditions, from 20°C to 80°C. Beams were heated from the strengthened side with the use of linear infra-red radiators and when the temperature of the adhesive layer reached the predetermined value, beams were loaded to failure. Noticeable impact of temperature appeared from about 50°C. In all cases failure was followed by delamination. Differences in behavior of CFRP and SRP strengthened beams were observed. Delamination of CFRP strip appeared in unexpected way, without any specific symptoms, while SRP failed with grater deflection and lower mid-span strains compared to the beam tested at room temperature. At temperatures above 65°C appears significant bearing capacity degradation. It means that CFRP strengthening, which could be subjected to direct sun exposition, should always be protected by thermal insulation.