Temperature Effects in Adhesively Bonded FRP Strengthening Applied to Steel Beams: Experimental Observations

FRP plates can be used to strengthen a steel beam in flexure, but this method relies critically upon the adhesive used to bond the FRP plate to the existing steel member. When the temperature of the strengthened beam is increased, differential thermal expansion occurs between the steel and FRP. In addition, the glass transition temperature of a typical two-part ambient-cure epoxy adhesive is typically between about 50°C and 65°C, and the stiffness and strength of the adhesive will decrease at temperatures somewhat below the glass transition temperature. This paper reports tests conducted on steel beams strengthened with CFRP plates and ambient-cure epoxy adhesive. Load was applied to the beams in four-point bending, and the temperature of the strengthening was then increased until failure occurred. Slip deformations were directly observed across the adhesive joint, giving an indication of the performance of the strengthening at elevated temperatures. The consequences of this preliminary study upon the design of externally-bonded FRP strengthening for steel structures are discussed.