Experimental study and numerical simulation of long-term behavior of timber beams strengthened with near surface mounted CFRP bars

The near-surface mounted (NSM) fiber reinforced polymer (FRP) method has been proven effective and is increasingly applied to strengthen timber beams. However, few studies on the long-term response of such FRP-reinforced timber beams are available. This paper presents the experimental results of three full-size timber beams tested under sustained load for 1200 days, including an unstrengthened reference beam and two CFRP NSM-reinforced timber beams. The strengthened timber beams exhibited similar creep responses as the reference beam. However, the creep-induced strain and curvature at the mid-span section of the strengthened beams were lower than those of the reference beam, which reflects the restraining effect of the CFRP bar. At 50 % of the ultimate load capacity, the strain distribution at the mid-span section of each specimen remained linear, following the plane section assumption. The strain measurements were observed to increase with increases in ambient temperature and relative humidity. The parabolic model, Burgers model and a five-parameter model were employed to predict the long-term deflection of the reference specimen and equations were fitted for these three models. Comparison between the prediction and experimental results shows that the five-parameter model has the greatest accuracy in both the primary and secondary creep phases. Finally, a numerical model was developed using the creep equation available in ANSYS to simulate the long-term deformation of each specimen. The coefficient in the creep equation was defined as being constant at each time step. Good agreement between the simulation and experimental results was observed.