FRP reinforcement is an alternative to conventional steel reinforcement as it combines high tensile strength and resistance to corrosion. However, the compressive strength is still subject to research.

Some researchers have found out that FRP reinforcement can have a negative effect on the concrete/FRP-composite compressive strength (see Bochmann, J.: Carbonbeton unter einaxialer Druckbeanspruchung [2019]).

For RC columns reinforced longitudinally and transversally with FRP, scientists observed an increase in load-bearing capacity (see Afifi, Mohamed & Benmokrane: Strength and Axial Behavior of Circular Concrete Columns Reinforced with CFRP Bars and Spirals [2013]).

The question arises therefore on how to evaluate the effect of FRP reinforcement in the compression zone of a concrete member subjected to flexural loads. One can argue that as long as ultimate compression strain at limit state (and elastic modulus) are higher than that of the concrete, the FRP reinforcement would increase the overall load-bearing capacity. On the other hand, the risk of a negative effect for example due to the transversal isotropic material behaviour and spalling of the concrete cover should also be considered.

How are your thoughts about this? Do you know of any research articles regarding this topic?