Bond behaviour of Steel Reinforced Polymer strengthening systems

Steel Reinforced Polymer (SRP) systems, consisting of Ultra High Tensile Strength Steel cords and epoxy resin, are emerging as an effective and cost efficient solution for the externally bonded strengthening of structures. Their applications in civil engineering are more recent than those with Fibre Reinforced Polymers (FRP) employing carbon, glass or aramid textiles, and their mechanical properties still need to be deeply investigated. This paper presents an experimental study on SRP reinforcements comprising textiles with 4, 12 and 18 cord/in density. First, the mechanical properties of both textiles and SRP composites were derived through direct tensile tests. The shear bond behaviour, which is crucial for the effectiveness of most applications, was then investigated on strong and weak concrete, tuff, clay brick and brick masonry substrates, providing information on bond strength, failure mode, load-slip response and effective transfer length. Finally, test results and data available in the scientific literature are collected to calibrate the tuning coefficients for the estimate of the bond strength according to the design relationships provided by the Guidelines on FRP.