AbstractThis study proposes a relation for the failure strain of externally bonded reinforcement on groove (EBROG) joints derived through multivariate regression analysis on the experimental results. In addition to the conventional parameters of concrete compressive strength and groove dimensions studied as independent variables, a novel descriptor variable of great effect, called width of fiber-reinforced polymer (FRP) sheet on a single groove, is also introduced for the first time. Using these descriptors and their variations, 27 specimens are strengthened via the EBROG method and subsequently subjected to the single lap-shear test. First, the proposed relation is assessed with respect to its goodness of fit using certain statistical indices, which reveals a good agreement between estimated and measured values. The relation is also verified in terms of its efficiency and accuracy through a comparison with a previous model using 65 specimens in three groups previously reported in the relevant literature. The comparisons indicate the superior accuracy of the proposed relation in estimating the failure strain of EBROG joints and its higher generality as compared to the rival model.