Strain assessment for the design of NSM FRP systems for the strengthening of RC members

•Effectiveness of FRP in strengthening of existing constructions is investigated.•Bond tests on different types of near surface mounted (NSM) reinforcement are showed.•Further results of bond tests available in literature are collected and analysed.•A relationship to predict debonding strain of the FRP NSM strengthening is calibrated.•The calibration is in accordance with the “design by testing approach” suggested by Eurocodes.

Recently, experimental results of bond tests performed by several researchers to measure the performance of Fibre-Reinforced Polymer (FRP) applied according to near-surface mounted (NSM) strengthening techniques have indicated that the mechanical properties of materials and the surface properties of FRP reinforcement as well as the groove geometry and the test setup can affect the bond behaviour of this strengthening system. Experimental tests also show that the NSM technique could represent a sound alternative to FRP Externally-Bonded Reinforcement (EBR) systems because it allows the FRP tensile strength to be better exploited. Herein, the results of bond tests of different types of NSM FRP reinforcement carried out by the authors and other results available in the literature are collected and analysed in terms of the maximum bond shear stress and maximum strain at failure. The results are analysed to provide an experimentally calibrated relation aimed at predicting both the average and characteristic values of the maximum strain of NSM FRP reinforcements in the case of bond failure, according to the design assisted by testing approach.