A comparison of the influence of nonlinear and linear creep on the behaviour of FRP-bonded metallic beams at warm temperatures

Creep of an FRP-strengthened metallic beam under cyclic temperature and cyclic load

“…Differential thermal expansion between the FRP and Ibeam has a significant effect on the behaviour of the bonded structure: in the short term, DTE can be beneficial for temperatures above the temperature at which the strengthening is applied or detrimental for temperatures below this. This is known from previous studies at constant temperature [14,15], but applying a constant temperature is a very extreme case. The current work examines the magnitude of creep (and associated redistribution of stress within the strengthened beam) resulting from cyclic temperatures and load over timescales up to 50 years.…”

“…Most previous studies of the effects of creep on FRP-strengthened metallic beams have only considered the performance of the strengthened beam under constant elevated temperature and constant load conditions [11][12][13][14][15], leaving it unclear whether the long-term effectiveness of the FRP strengthening is a serious concern when subject to daily variations in ambient temperature and applied load.…”

“…The analysis in this paper uses a linear viscoelastic constitutive material model for the structural adhesive that was previously developed by the authors [14] for a typical two-part, ambient-cured epoxy resin used in FRP-strengthening (Sikadur 330) [24]. A nonlinear viscoelastic model is not used in this work, as nonlinear viscoelasticity was shown to have limited influence on the behaviour of the FRP-strengthened I-beam [15]. Using a linear viscoelastic model also allows a 2D model to be used (rather than the 3D model required for a nonlinear viscoelastic constitutive response in the Abaqus software used here [25]), significantly reducing the computationally time.…”

“…This demonstrated how linear viscoelasticity of the adhesively bonded joint can result in additional slip between the FRP and I-beam that increases with time, and how the reduced the efficiency of strengthening may need to be examined as part of the design of the strengthening. The authors went on to study whether it is necessary to examine a nonlinear model for creep [15]; however, this only caused slightly greater slips and increased CFRP stress at shorter timescales, so that a linear slip model is sufficient in most practical cases.…”

“…These studies have been constrained to lap-shear tests, however, and have not analysed the impact of temperature and load cycles on the response of FRP-strengthened beams, with its far longer adhesive joint. They did not properly consider the viscoelasticity of the adhesive, which could bring significant time-temperature related creep deformation to the bonded joint [11,[14][15][16].…”