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Five reinforced concrete bridge bents constructed in 1963 were obtained from the demolition of I-15 in Utah and one bent was newly constructed to the specifications of the existing bents. The bents were retrofitted using varying methods. The methods included concrete patches, epoxy crack injection, and carbon fiber reinforced plastic (CFRP) wraps. After the bents were repaired, their cantilevers were tested to failure. For the bents tested, the concrete patches did not conclusively affect the capacity of the bents, and were therefore unnecessary for structural purposes, but served more of a cosmetic and visual confidence need. The epoxy crack injection did not restore the strength or stiffness of the bent, but it still is a viable repair method of sealing cracks to protect the reinforcement from corrosion. The CFRP wraps were successful in strengthening and stiffening the bridge bents. The CFRP wrapped bents were about twice as stiff as the other bents tested.
Summary available via the World Wide Web as of 8/29/2002 from the Bridge Research and Information Center web site,
Large numbers of reinforced concrete deck girder (RCDG) bridges were built during the highway infrastructure boom of the 1950's. The advent of standardized deformed steel reinforcing bars during this time allowed for straight bar terminations in flexural tension regions. Designers of the time terminated reinforcing bars where they were no longer required by calculation and did not account for additional demands from the combination of shear and flexure. The design provisions of the time allowed higher shear stresses in the concrete than allowed in standards today which reduced the required quantity of transverse reinforcing steel. In addition, heavier trucks and higher traffic volumes on roadways today have greatly increased the service loading on these bridges. Engineers evaluating these older RCDG bridges often determine unsatisfactory load ratings due to flexural anchorage deficiencies in the girders, especially when the influence of shear is considered. These deficiencies result from inadequate capacity compared to current design standards due to poor cutoff details used in the initial design. Strengthening methods are necessary because comprehensive replacements of the large number of bridges are not economically feasible. Experimental research was conducted to evaluate the behavior of poorly detailed flexural anchorages and to develop methods to strengthen them. Realistic vintage girder specimens were constructed, retrofitted, instrumented, and tested to failure. The specimens reported in this thesis were full-scale inverted-T (IT) beams. Some of the specimens contained straight bar terminations crossing a preformed diagonal crack in the flexural tension region to investigate the influence of shear on the retrofit schemes. Instrumentation focused on measurement of the reinforcing steel stresses surrounding the diagonal crack and along the development length of the cutoff bars. Using results of past research to quantify the behavior of girders with straight-bar flexural anchorages in flexural tension regions, an innovative strengthening technique was developed using either near-surface mounted (NSM) stainless steel or titanium. Results from the NSM strengthening technique demonstrated the ability to delay or prevent flexural anchorage failures, with increased deformation capacities and increased strengths from 17% to 39% over baseline specimens. To show the success of this research and the immediate need for strengthened flexural anchorages, this research has already been implemented on a bridge in Mosier, Oregon. This groundbreaking research is described in detail in Appendix F.
Typical reinforced concrete (RC) bridges built prior to 1970 were designed with minimum seismic consideration, leaving numerous bridges highly susceptible to damage following an earthquake. In order to improve the seismic behavior of substandard RC bridges, this study presents the seismic performance of reinforced concrete bridge bents retrofitted and repaired using Buckling-Restrained Braces (BRBs) while considering subduction zone earthquake demands. In order to reflect displacement demands from subduction ground motions, research studies were conducted to develop quasi-static loading protocols and then investigate their effect on structural bridge damage. Results suggested that subduction loading protocols may reduce the displacement ductility capacity of RC bridge columns and change their failure mode. The cyclic performance of reinforced concrete bridge bents retrofitted and repaired using BRBs was experimentally evaluated using large-scale specimens and the developed loading histories. Three BRB specimens were evaluated with the aim of assessing the influence of these components on the overall performance of the retrofitted and repaired bents. Additionally, subassemblage tests were conducted in an effort to study the response of these elements and to allow for refined nonlinear characterization in the analysis of the retrofitted and repaired systems. The results of the large-scale experiments and analytical studies successfully demonstrated the effectiveness of utilizing buckling-restrained braces for achieving high displacement ductility of the retrofitted and repaired structures, while also controlling the damage of the existing vulnerable reinforced concrete bent up to an operational performance level.