Key Parameters in the Calculation of the Reinforcement of Rectangular Columns with FRP. Review of Design Guidelines and Comparison with Experimental Results

It has been shown after several studies, that in view of the need to strengthen the deficient columns of reinforced concrete (RC), one of the most attractive and used techniques to increase strength and strain capacity, is the confinement of concrete whit FRP (fibre reinforced polymers). It is well known that the confinement of square or rectangular columns is less efficient than the confinement of circular columns. Most of the experimental studies focused on the behaviour of small-scale concrete circular specimens. However, in practice, the most typical findings are the square / rectangular columns of reinforced concrete (RC) on a large scale, so that there is still significant uncertainty in the models used to calculate the reinforcement with FRP and their applicability (especially in the case of columns with rectangular section). One of the key parameters in the prediction of the models is the ultimate strain of the FRP. Some models consider a strain efficiency factor of approximately 0.6, the value of which has been determined from tests on small-scale cylindrical specimens. This paper presents an analysis of the design formulations proposed in the main published international guidelines and compares them with the experimental results of larger square and rectangular section specimens (intermediate and full scale).