Nonlinear viscoelastic analysis of reinforced concrete cross-sections strengthened with externally bonded or near surface-mounted FRP reinforcement

Strengthening and retrofitting of existing structures is often preferred to demolition and reconstruction due to economic and preservation reasons. In addition to traditional techniques, externally bonded (EB) and near surface mounted (NSM) fiber-reinforced polymer (FRP) composites represent an effective strengthening solution particularly for reinforced concrete (RC) members. When strengthening or retrofitting is performed due to an increase in the applied load, the long-term deformation of the RC strengthened element should be studied accounting for the cracked reinforced concrete long-term behavior. In this paper, the evolution over time of the curvature of an RC cross-section strengthened with FRP composites at an early age is studied. A numerical approach is proposed to obtain the time-dependent cross-section response considering pure bending, viscoelastic behavior of compressed concrete, concrete cracking, and concrete shrinkage. In addition to the accurate numerical approach, an approximate approach is also proposed to simplify the analysis. The accuracy of this approximate approach is evaluated by comparison with the general numerical solution. Three case studies are proposed. They show that the approximate approach provides accurate estimations of the temporal evolution of the cross-section curvature, which can be used to obtain the deflection of the associated structural member.