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

Abstract

Metallic beams can be strengthened using fibre reinforced polymer (FRP) plates that are adhesively bonded to their soffit. This relies critically upon the bonded adhesive joint, and because the adhesives are viscoelastic it is known that creep at warm services temperatures can potentially result in large slips that can reduce the effectiveness of the strengthening. This paper examines the impact of adhesive creep upon the performance of an FRP-strengthened metallic beam when subjected to daily temperature cycles and daily load cycles. A finite element (FE) study was conducted that incorporates a linear viscoelastic constitutive model for the adhesive, temperature and load cycles of up to 50 years were considered, and the behaviour of the strengthened beam was examined. Differential thermal expansion between the FRP plate and metallic beam is shown to be significant because it results in both (a) additional instantaneous shear stress across the adhesive joint and (b) the shear stress due to sustained differential thermal expansion results in additional creep of the adhesive that can further reduce the effectiveness of the strengthening. An equivalent cumulative time approach is demonstrated to predict the creep response of the strengthened metallic beam without the need for a complex cyclic analysis.