Time-dependent behavior of RC members strengthened with FRP laminates

Strenghtening of concrete structures with fiber-reinforced plastic (FRP) composites epoxy-bonded to their tension faces appears to be a method with a high potential for increasing the strength and stiffness of existing members. The writers aim at developing a fundamental understanding of the time-dependent (creep andshrinkage) behavior of reinforced-concrete beams strengthened with FRP laminates. An analytical procedure is given first for the deformation of cross sectionsbased on the age-adjusted effective-modulus method for concrete, Findley's model for composite materials, and a stress-relaxation procedure to yield the cross-sectionalstresses and strains as a function of time. Parametric studies assessing the effect of the type and the area fraction of composite material and of the area fraction of steel reinforcement on the long-term response of strengthened elements are also presented. Finally, the analytical model is used to predict the deflections of concrete beams strengthened with FRP laminates of different thicknesses, and an experimental program is described confirming the analysis.