Experimental Evaluation of Flexural Strengthening of Reinforced Concrete Girders with Near-surface Mounted Titanium Alloy Straight Bars

The installation of near-surface mounting (NSM) titanium alloy bars (TiAB) has become an emerging method for strengthening strength-deficient reinforced concrete (RC) bridge girders to extend their service life. As a result, several studies have been conducted using NSM TiAB. Most of these studies focused on flexural strengthening using hooked-bonded TiAB because the American Association of State Highway and Transportation Officials (AASHTO) guide for NSM TiAB design allows only hooked-bonded TiAB for strengthening. Therefore, an experimental program was undertaken to investigate the behavior of full-scale RC bridge girders strengthened with straight-bonded NSM TiAB for both positive- and negative-moment flexural-strengthening purposes. Four beam specimens were tested for positive moment strengthening including one unstrengthened specimen for comparisons, while evaluating two TiAB types with different surface deformation. Additionally, three beam specimens were tested with a single type of TiAB for evaluating negative-moment strengthening, including one unstrengthened specimen. The bonded TiAB lengths used for specimens were determined according to the guidance available in i) the AASHTO guide for the design of NSM TiAB or ii) ACI 440.2, to achieve the nominal flexural capacity of the strengthened beams with TiAB yielding. The experimental results revealed that use of straight-bonded NSM TiAB for flexural strengthening is effective when ACI 440.2 provision is considered to prevent the concrete cover delamination failure mode. Additionally, the two TiAB types that were evaluated exhibited similar flexural behavior and either type can be used for the flexural strengthening of bridge girders.