Reversible techniques for FRP-confinement of masonry columns

Heritage buildings worldwide are primarily masonry construction. Over the centuries, these structures have demonstrated a high vulnerability in seismic events. The seismic protection and retrofitting of these historical structures require an effective structural solution, without compromise, cover or loss of architectural and artistic value. For these scenarios, the use of Fiber Reinforced Polymers (FRPs) is discouraged since removability of the intervention is often a mandatory requirement, and the polymeric adhesives bond the fiber to the masonry substrate, eliminating the possibility of preserving the underlying material during a replacement operation. In FRP-strengthening, the force transfer from the substrate to the FRP occurs by means of bond stresses. However, in the case of column confinement, while full bond is nevertheless developed through the adhesive, it is not necessary for the effectiveness of the confinement. Instead, the confining pressure is applied by the FRP when transversal dilatation of the column is mobilized. Thus, with the exception of the overlapping regions, an FRP retrofit for column confinement works due to a contact phenomenon instead of bond. In this context, new FRP-confinement techniques, based on contact rather than adhesion, can be developed. This paper presents research on fully-reversible contact-based techniques for FRP-confinement. Three different techniques were developed and demonstrated by the authors. Each technique was experimentally evaluated through compression tests of small-scale limestone cylinders. The reversibility of each technique was verified through comparison of the substrates before the FRP-confinement and after the testing. The effectiveness of each technique was evaluated by comparing the compressive strength and the deformability with those obtained for unconfined specimens. The concepts show promise as effective and reversible strengthening techniques.