The mechano-sorptive creep behaviour of basalt FRP reinforced timber elements in a variable climate

The use of Fibre Reinforced Polymer (FRP) reinforcement has been shown to improve the short-term flexural behaviour of timber elements. This is particularly important when reinforced elements are subjected to a variable climate condition, which is known to accelerate long-term or creep behaviour. In this paper, both unreinforced and Basalt FRP reinforced beams are subjected to creep tests at a common maximum compressive stress of 8 MPa over a 75-week period. Results demonstrated a significant reduction in total creep deflection due to the FRP reinforcement. Using matched groups, experimentally measured total strain behaviour is decomposed into the elastic, viscoelastic, mechano-sorptive and swelling/shrinkage strain components. Analysis has shown that the mechano-sorptive component is similar in unreinforced and reinforced beams. The reduction in creep behaviour of the reinforced members was primarily due to the restrained swelling/shrinkage response of the reinforced beams and was independent of the mechano-sorptive effect. This finding demonstrates the positive influence of FRP reinforcement on the long-term behaviour of timber elements and indicates a potential to describe the long-term deflection performance of FRP reinforced elements from short-term swelling/shrinkage tests.