Confining concrete members with FRP systems: Predictive vs design strain models

Several analytical models are available in the literature to predict the compressive strength and the ultimate strain of the FRP confined concrete. The reliability of such models is often affected by an inaccurate definition of the “effective” confining pressure exerted by the FRP jacket and/or by an incorrect evaluation of the reduced confinement effectiveness in the case of square and rectangular cross sections. In this paper, following a previous study on the compression strength, an investigation on the ultimate strain of the FRP confined concrete is presented. To this aim, a large database including results from compression tests performed on over 450 FRP confined concrete cylinders was considered, and some of the most accredited predictive strain models were recalibrated through best-fit analyses of the experimental data. Finally, a probabilistic procedure was applied in order to define design models; for this purpose only data sets for which the unconfined concrete strength was below 40 MPa were considered.