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Application of titanium alloy bars for strengthening reinforced concrete bridge girders (part a: shear) : final report.

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  • Creators:
  • Corporate Creators:
    Oregon. Dept. of Transportation. Research Section
  • Corporate Contributors:
    United States. Federal Highway Administration
  • Subject/TRT Terms:
  • Publication/ Report Number:
    FHWA-OR-RD-18-01;SPR 775
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    United States
  • Edition:
    Final report
  • Corporate Publisher:
    Oregon. Dept. of Transportation. Research Section
  • Abstract:
    Large numbers of conventionally reinforced concrete bridges (RC) were constructed during the interstate

    highway expansion of the 1950’s and remain in the national inventory. Coincidently, deformed steel reinforcing

    bars were standardized. The standardized deformation requirements dramatically changed bond provisions in all

    relevant design codes and designers began to use straight-bar terminations of the flexural reinforcing bars where

    they were no longer required by calculation. This produced terminations in flexural tension zones without special

    detailing provisions. At the same time, design codes overestimated the concrete contribution to shear resistance

    and thus designs provided less transverse steel than permissible by modern standards. These poor details

    combined with heavier loads have resulted in diagonal cracking of the girders. Application of modern design

    provisions to assess vintage RC members typically results in low predicted capacity. Load restrictions or

    replacement of bridges is expensive and thus structurally effective and economical strengthening approaches are

    required.

    Near-surface mounting (NSM) of supplemental reinforcing bars has emerged as a common retrofit method for

    strengthening RC structures. In this method, bars are bonded with an adhesive within grooves that are cut into

    the surface of the member. The most common reinforcing material used in the NSM application is fiber

    reinforced polymer (FRP). FRP materials are elastic until fracture thus providing no ductility. In addition, they

    can debond prematurely limiting the effectiveness of the repair. For this reason, new titanium alloy bars (TiABs)

    were developed as a potential alternative for FRP bars in NSM applications.

    Small diameter (1/4 in.) NSM TiABS were applied to full-size bridge girder specimens that were shear deficient

    and tested to failure in the laboratory. Two different epoxy materials were considered, as well as two different

    configurations of TiAB bars (single leg and double leg stirrups). The combined effects of high-cycle fatigue

    loading and repeated freeze-thaw exposure were investigated to assess long-term durability of the proposed approach and materials.

    Results showed that NSM TiABs provided significant increases in the strength when compared to

    similar unstrengthened specimens. The TiABs were observed to achieve the yield stress prior to/at ultimate.

    Anchorage of the TiABs was sufficient to produce rupture over the main diagonal cracks. The double leg

    TiABs were easier to construct and provide additional confinement across the beam soffit. It was determined

    that some reduction in strength was observed for one of the epoxy materials due to the combined fatigue and

    environmental effects. Three methods were used to analyze the experimental results which could conservatively

    predict strength. Strength reduction factors were developed for each method to be used in design.

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