Strengthening of Low-Strength Concrete Columns with Fibre Reinforced Polymers. Full-Scale Tests

This article belongs to the Special Issue Selected Papers from the REHABEND 2020 Congress.Confinement of columns with externally bonded fibre reinforced polymers (FRP) sheets is an easy and effective way of enhancing the load carrying and strain capacity of reinforced concrete (RC) columns. Many experimental studies have been conducted on cylindrical small-scale un-reinforced concrete specimens externally confined with FRP. It is widely accepted that confinement of square or rectangular columns is less efficient than the confinement of circular columns. The theoretical models for rectangular sections are mostly based on approaches for circular columns modified by a shape factor, but the different models do not give similar results. This paper presents an experimental program on large-scale square and rectangular RC columns externally strengthened with carbon FRP sheets and subjected to axial load. The main variables were the side-aspect ratio of the cross-section, the radius of curvature of the corners, and the amount of FRP reinforcement. The results show that the FRP confinement can increase the strength and strain capacity of rectangular concrete columns with low strength concrete. The FRP hoop ultimate strain was much lower than the material ultimate tensile strain obtained from flat coupon tests and the strain efficiency factor achieved in the tests was less than the value usually recommended by design guides.This work was supported by research project BIA2016-80310-P, funded by AEI (Research State Agency of the Spanish Ministry of Science and Innovation) and the FEDER (European Regional Development Fund). Acknowledgments: The authors acknowledge BETAZUL S.A. and SIKA S.A.U. for performing the strengthening work and providing FRP materials. V. J. Castro acknowledges the financial support (FPI grant BES2017-080647) of the Spanish MICINN and the European Social Fund.Peer reviewe