Multiscale viscoelastic analysis of FRP-strengthened concrete beams

A multiscale framework with an elastic reinforced concrete (RC) beam bonded to a fiber reinforced polymer (FRP) plate (connected by an adhesive layer with viscoelastic properties) is established in this research; this framework is proved to be fast and efficient in avoiding time integration and complex meshing in existing FE models. The FRP plate is composed of elastic fibers and surrounded by viscoelastic polymers whose effective properties are generated by the locally exact homogenization theory. According to the correspondence principle, the viscoelasticity problem can be solved in the Laplace domain as an elasticity problem. This leads to solutions that can be transformed back to the time domain through Zakian's numerical method. To validate the present method, comparisons with the simulations reported in literature are presented. The effects of cracks, prestress in FRP plates, microscale fiber content, and temperature on the long-term behavior of FRP-strengthened RC beams are effectively investigated using the present method. Through the recovery of stress relaxation within the ad-hesive layer, the present technique is found capable of conveniently predicting the long-term behavior of FRP-strengthened RC beams, providing a robust tool for structural design and maintenance.