Mechanically Fastened CFRP to Retrofit Existing Prestressed Concrete and Steel Bridge Beams

Prestressed concrete C-channels and cored slabs, and steel beams of various shapes and forms make up a significant percentage of the common bridge superstructure systems used by North Carolina Department of Transportation (NCDOT). Many such bridges are in varying states of distress and require retrofit to extend their useful service life prior to major rehabilitation or superstructure replacement. The challenge is to develop retrofit techniques that are durable, easy to install, monitor and maintain, and that may be applied to the range of prestressed concrete and steel beam types. Critically, NCDOT must also be able to rate the proposed retrofit using approved American Association of State Highway Officials (AASHTO) methods before it may be applied in the field. In many cases the retrofit may be considered temporary since the bridge may be scheduled for replacement in the near future. Temporary strengthening is intended to provide the ability to maintain a sufficiently high operating rating to keep the bridge functional while replacement is scheduled. In lieu of an acceptable retrofit, the bridge may need to be load posted or closed, often resulting in significant detours and disruption. Previous collaboration with NCDOT (TA-2014-05) demonstrated analytically that mechanically-fastened (MF) carbon fiber-reinforced polymer (CFRP) plates may be used to restore the ultimate flexural capacity of deteriorated prestressed C-channel beams. The use of mechanical fasteners eliminates the need for an epoxy adhesive bond typical of common FRP strengthening systems, which means that the MF-CFRP strengthening system is effective immediately upon installation, and simplifies the installation, field inspection and monitoring of the strengthening system. The shortcoming of the existing system is that it does not increase the cracking moment resistance of the strengthened prestressed concrete beam and hence, the operating rating remains unchanged and the strengthening technique is not approved for use in the field. It is hypothesized that a similar mechanically fastened strengthening system could be applied to damaged or deficient steel girders, and that rating steel girders might be less complicated since there is no "cracking moment" to consider in load rating. Two effective alternatives, which form the basis for this research project, are available to address the current inability to increase the operating rating using the otherwise desirable MF-CFRP system which include: (i) the ability to prestress the MF-CFRP plate during the installation process which will have the effect of closing existing flexural cracks and increasing the cracking moment by effectively inducing a camber in the existing beam in the same way that internal steel prestressing does - the same may be achieved by propping the beam prior to installing the MF-CFRP; and (ii) the development of software analysis tools for use by NCDOT load rating engineers that will enable a complete sectional analysis of a (strengthened) prestressed concrete beam for any generic cross-section, which has proven to be a limitation of existing software tools used by the NCDOT. It is the development of these two tools, which were not recognized prior to NCDOT Technical Assistance No. TA-2014-05 and hence, was beyond the original scope of work, that will finally enable the use of FRP strengthening systems by NCDOT. Research products will include: State-of-the-practice reference document; guidelines and specifications covering the analysis, design, installation and field inspection of MF-CFRP retrofitted beams; a complete solution to extend the service life of deteriorated prestressed concrete and steel beams using a durable FRP strengthening system considering both operational load rating and flexural capacity; a cost benefit analysis of the proposed MF-CFRP retrofit technique; and a user-friendly analysis tool to facilitate load rating calculations for any prestressed concrete and steel beam sections.


  • English


  • Status: Active
  • Contract Numbers:


  • Sponsor Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Project Managers:

    Kadibhai, Mustansir

  • Performing Organizations:

    North Carolina State University

    Department of Civil Engineering, Campus Box 7908
    Raleigh, NC  United States  27695-7908
  • Principal Investigators:

    Seracino, Rudolf

  • Start Date: 20170801
  • Expected Completion Date: 0
  • Actual Completion Date: 20200731
  • Source Data: RiP Project 41775

Subject/Index Terms

Filing Info

  • Accession Number: 01641217
  • Record Type: Research project
  • Source Agency: North Carolina Department of Transportation
  • Contract Numbers: 2018-16
  • Files: RiP, STATEDOT
  • Created Date: Jul 19 2017 1:00AM