Glass transition effect of adhesive in timber beams strengthened with CFRP overlays

Silesian University of Technology, Department of Civil Engineering, Akademicka 5, 44-100 Gliwice, Poland

^* Corresponding author: rafal.krzywon@polsl.pl

Abstract

There are situations when timber structure requires strengthening caused by environmental deterioration or changes in load conditions. Its mechanical performance can be increased by use of externally bonded high strength fibre reinforced composite (FRP). The place of application increases the sensitivity of this technique to environmental effects, including heating by the sun rays. Surface temperature can exceed 70 °C, while usually as safe is considered 45 °C. Paper describes the tests of timber beams strengthened with two types of composites: unidirectional CFRP sheet and CFRP strip. They were heated at various temperature ranges and tested in bending. Out of the nine tested beams, only one heated to 95 °C was not damaged by the delamination of the composite overlay, remaining beams have not been destroyed due to achieved deflection exceeding the press cylinder range or were failed due to rupture of carbon fibres. The influence of the temperature was better recognizable in differences of deflections and strains caused by the creep in the adhesive layer weakened by temperature. It should also be emphasized that got results are much better than for commonly tested reinforced concrete beams, where delamination caused failure slightly above 65 °C.