Impact of structural adhesive creep on the performance of CFRP-strengthened steel beams

This paper examines the viscoelastic creep response of the structural strengthening epoxy adhesive and develops a viscoelastic constitutive model for numerical analyses to assess its impact on the long-term performance of carbon fibre reinforced polymer (CFRP)-strengthened steel beams. The numerical studies explore the behaviour of CFRP-strengthened steel beams subjected to both three-point and four-point bending over a one-year period, with temperatures ranging from −20 to 60 °C. The results revealed that the stiffeners could reduce the deflection and peak stress in the steel under four-point bending, yet they had the opposite effect under three-point bending. Furthermore, whilst the larger CFRP plates could reduce the slip at the plate ends, they provided only a limited enhancement in the strengthening effectiveness. The impact of viscoelastic creep in the adhesive is more marked and apparent, particularly at higher temperatures. Over time, the increased slip leads to a rise in maximum stress and deflection of the steel beams, thereby diminishing the effectiveness of the strengthening. A low-temperature environment can mitigate these negative impacts, whereas elevated temperatures can significantly exacerbate them. Notably, at a moderate temperature of 30 °C, the maximum CFRP stress can already be reduced by 32.25 %, which corresponds to an increase in steel stress by 4.15 %. Therefore, in practical applications at warm service temperatures, the creep of CFRP-strengthened steel beams should be carefully considered to ensure their long-term safety.