United States Department of Transportation
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Methods for strengthening reinforced concrete bridge girders containing poorly detailed flexural steel using near-surface mounted metallics.
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2015-08-01
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Abstract:Many older reinforced concrete deck girder (RCDG) bridges contain straight-bar terminations of flexural reinforcement in
flexural tension zones without special detailing. Common bridge design practice of the 1950s did not consider the additional
demands on the terminated bars from shear and flexure. Moreover, application of modern design code provisions and use of
heavier trucks contribute to insufficient bridge load ratings when evaluating flexural anchorages in existing RCDG bridges.
Replacement of bridges with poor ratings due to localized deficiencies is not economically feasible and thus strengthening
methods are necessary.
The goal of this research was to investigate methods for strengthening deficient flexural steel anchorages using
supplemental surface bonded metallic reinforcing bars. Full-scale reinforced concrete girder specimens with typical vintage
details and materials were used as test specimens. The specimens were constructed with flexural anchorage deficiencies by
terminating some of the embedded flexural bars past a 45° preformed diagonal crack. The terminated bars had only one-third of the code-prescribed development length past the diagonal crack.
A strengthening technique called near-surface mounting (NSM) was applied to the specimens. Two metallic materials were
selected for the NSM reinforcement: titanium and stainless steel. These materials were chosen because of their high
strength, ductility, environmental durability, and ability to form mechanical hooks at the ends of the bars. This study found
that the NSM strengthening technique with metallic materials increased the deformation and load capacity of all
specimens. In addition, a case study was performed to demonstrate the flexural strengthening for the Mosier Bridge
overcrossing of I84 in Oregon. The case study demonstrated that the techniques and materials applied to the girder were
able to achieve the required strength and provided good deformation capacity.
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