Bond Tests of Short NSM-FRP and Steel Bar Anchorages

Performance of near-surface mounted (NSM) bars as additional reinforcement in strengthening of existing reinforced-concrete construction largely depends on the development capacity of the bar inside the groove. This is controlled primarily by the surface characteristics of the bar and its interaction with the surrounding groove filler and the cover concrete. In this paper, the bond strength of short NSM-bar anchorages is explored experimentally, using a modified eccentric pullout test specimen designed to alleviate some of the deficiencies associated with bond testing. A total of 45 tests were conducted to study the influence of the most important technological parameters of this upgrading method, namely the groove dimensions, the embedment length, and the surface pattern of the bars. NSM bars were 12mm diameter rods: CFRP bars used had a sandblasted surface and winding helical lengthwise indentations. Steel bars were either standard deformed bars or smooth reinforcement. The variety of bar type considered was intended to highlight and to quantify through the tests the bond strength that may be mobilized by postinstalled reinforcement according to surface profile and stiffness. Test results are used to establish a limit-state bond-slip model for near-surface mounted bars, so as to enable implementation of this emerging technology in practical design.