Structural Design and Analysis of Post-Tensioned Concrete Structures with Flexible Fillers

Grouted and bonded post-tensioning tendons are the predominant post-tensioning systems used in bridges in the United States. However recent durability issues of grouted tendons have prompted state DOT’s to move toward unbonded tendons using flexible fillers to facilitate future replacement of potentially corroded tendons. Structural members can be prestressed utilizing unbonded internal tendons (UIT), unbonded external tendons (UET), combined unbonded internal and external tendons (CUT), bonded tendons (BT) or combinations of bonded and unbonded tendons (CBUT). While flexible fillers have been used in Europe for decades, this new direction in post-tensioning requires reevaluation of the current AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) for post-tensioned structures with UIT, CUT and CBUT. The proposed study consists of three parts: (1) analysis and experimental evaluation of shear in structures with internally unbonded tendons in the webs of structural members, (2) an analytical study to evaluate the flexural behavior of structures with UIT, CUT and CBUT, and (3) an evaluation of the resistance factors for structures with UIT, CUT and CBUT. The applicability of the Modified Compression Field Theory (MCFT) for shear design of bridges utilizing unbonded tendons is somewhat ambiguous because the theory is formulated based on membrane elements with well-distributed, bonded reinforcement. In unbonded segmental construction, there is no continuous bonded longitudinal reinforcement at the match-cast joints to resist in-plane axial tension stress at the local level. External or internal unbonded tendons can only resist global elongation between anchorage points. Therefore this research is critical to determine the applicability of MCFT in shear and torsion design for structures with UIT, CUT and CBUT. The current edition of AASHTO LRFD addresses both unbonded and bonded tendons separately and includes a section that addresses components with both bonded and unbonded tendons. The unbonded tendon approach is based on grouted external tendons resulting from research performed by MacGregor. In addressing the mixed condition (CUT or CBUT), it refers to a more rigorous detailed analysis or a conservative simplified analysis. This mixed condition however, has not been adequately evaluated and recent limited research has revealed the need to further explore this condition. While grouted external tendons are common practice, the new design philosophy could utilize internal unbonded tendons as well as combinations of unbonded and bonded tendons where the majority of the prestressing steel is unbonded. Internal unbonded tendons introduce voided ducts in the webs and flanges of I- and Box girders. Voided ducts reduce the structural capacity of a web to resist shear. Concerns have been raised whether it is sufficient to deduct the duct diameter from the web thickness in determining the concrete contribution. AASHTO LRFD currently differentiates resistance factors for bonded and unbonded state, however, it does not address a combined state. The shear and flexure design procedures should account for combining bonded and unbonded tendons in the same structural member. The objective of this research is to update the AASHTO LRFD Bridge Design Specifications design procedures for bridges with unbonded tendons or a combination of bonded and unbonded tendons. The research should include the shear provisions for webs with multiple unbonded tendons (duct voids), and update the associated resistance factors.

Language

  • English

Project

  • Status: Proposed
  • Funding: $800000
  • Contract Numbers:

    Project 12-118

  • Sponsor Organizations:

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Hanna, Amir

  • Start Date: 20180619
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01672546
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 12-118
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:03PM