Rational Shear Provisions for AASHTO LRFD Specifications: Technical Report

Prestressed concrete I-beams are used extensively as the primary superstructure components in Texas highway bridges. This research intends to solve one of the most troublesome problems in prestressed concrete, namely shear. The problem arises from the lack of a rational model to predict the behavior of prestressed concrete structures under shear action and the various modes of shear failures. Because of this deficiency, all the guidelines for shear design, such as ACI Codes and AASHTO Specifications, are empirical and have severe limitations. The research work was divided into two phases: Phase One consisted of developing the constitutive laws for prestressed concrete membrane elements and developing an analytical model for predicting the shear behavior of such elements. Crack simulation tests were first performed on rectangular prestressed beams to find the same cracking pattern of post-tensioned concrete with conduits as that in pre-tensioned concrete without conduits. Ten prestressed concrete panels (two series of five panels each) were tested. The first series of five panels was tested under sequential loading. The results of these tests were used to establish the constitutive relationships of materials (concrete and prestressing tendons). The second series of panels was tested under pure shear (a special case of proportional loading) to study the shear behavior of prestressed concrete membrane elements. Finally the Softened Membrane Model for Prestressed Concrete (SMM-PC) was developed to predict the response of prestressed concrete membrane elements under shear loading. Phase Two of the research dealt with testing of full-scale prestressed concreted I-beams and developing a new simplified equation for the shear design of prestressed concrete girders. Five TxDOT Type-A beams were designed, cast and tested to study their behavior in web shear and flexural shear failures. The results of these tests, along with the constitutive laws of prestressed concrete (developed in Phase One), were used to develop a new simplified equation for shear design of prestressed girders. Results of other prestressed beams available in literature were also considered to validate the design equation. The shear capacities of all the tested and referred beams were obtained using the new design equation and compared with the shear capacities obtained using ACI and AASHTO guidelines. Four design examples were prepared to illustrate the application of the new equation for design of prestressed girders. The new design equation was thereby extended to include non-prestressed girders. An example showing the design of a non-prestressed girder using the new equation was also completed. The research findings proved that the shear capacities of prestressed beams depended mainly on the compressive strength of concrete and the shear span to depth ratio of the beams. The effect of the amount of prestressing force and the angle of the failure planes of the beams on their shear capacities is insignificant.

  • Supplemental Notes:
    • Project title: Retional Shear Provisions for AASHTO LRFD Specifications. Report Date: October 2006; Published: January 2007.
  • Corporate Authors:

    University of Houston

    Department of Civil and Environmental Engineering, 4800 Calhoun Road
    Houston, TX  United States  77204-4003

    Texas Department of Transportation

    Research and Technology Implementation Office, P.O. Box 5080
    Austin, TX  United States  78763-5080

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Laskar, Arghadeep
    • Wang, Jun
    • Hsu, Thomas T C
    • Mo, Y L
  • Publication Date: 2007-1

Language

  • English

Media Info

  • Media Type: Print
  • Edition: Technical Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 216p

Subject/Index Terms

Filing Info

  • Accession Number: 01043630
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/TX-07/0-4759-1, Report 0-4759-1
  • Contract Numbers: Project 0-4759
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Mar 5 2007 2:39PM