Experimental Evaluation of Concrete Bridge Girders Flexural Strengthened with Near Surface Mounted Titanium Alloy Bars

Abstract

This research presents findings from a comprehensive study evaluating the feasibility of using Near-Surface-Mounted (NSM) Titanium Alloy Bars (TiAB) to strengthen structurally deficient reinforced concrete (RC) bridges in Alabama. The research aimed to provide a cost-effective, efficient solution to extend the service life of aging and strength-deficient highway bridges, focusing on a flexurally deficient bridge in Cullman, Alabama. An experimental program was developed to evaluate the behavior of large-scale, reinforced-concrete bridge girders using three NSM TiABs anchorage methods: i) hooked-bonded, ii) straight-bonded, and iii) hooked-unbonded; and two different types of TiAB. The experimental program included full-scale testing of 14 girders representative of the Cullman bridge, assessing both positive- and negative-moment strengthening. For hooked-bonded strengthening, the specimens were strengthened in accordance with the AASHTO NSM TiAB Guide for the design of NSM TiAB, and the requirements of ACI 318-19 were evaluated to handle the effect of stress concentrations at TiAB termination locations. For straight-bonded strengthening, the specimens were strengthened following the AASHTO NSM TiAB Guide for the design of NSM TiAB, and the requirements of ACI 440.2 were used to prevent the concrete cover delamination failure mode. The specimens were strengthened using the hooked-unbonded anchorage mechanism using the total strain theory and ACI 440.2 provisions. The test results indicate that flexural strengthening using NSM TiABs with hooked ends is effective when the effect of stress concentrations at the TiAB termination locations and the potential formation of inclined shear cracks in the flexural tension region are considered in the design. ACI 318-19, which has provisions to account for the impact of stress concentrations at internal reinforcement termination locations, should be used in addition to the AASHTO NSM TiAB Guide for the design of near-surface mounted titanium alloy bars. The experimental results of straight-bonded NSM TiAB revealed that flexural strengthening using straight-bonded TiAB is effective when the ACI 440.2 provision is considered to prevent concrete cover delamination failure. The hooked-unbonded method indicated that this method might be suitable for temporary use but it is inadequate for permanent strengthening. Two TiAB types that were evaluated exhibited similar flexural behavior, and either type can be used for the flexural strengthening of bridge girders. In addition, a strengthening implementation plan was proposed for the strength-deficient Cullman Bridge.