Considerations for the Design and Construction of Bonded and Unbonded Post-Tensioned Concrete Bridge Elements (2025)
Chapter: 1 Introduction
CHAPTER 1
Introduction
1.1 Background
Grouted tendons (bonded and unbonded) are predominantly used for post-tensioned concrete bridge elements in the United States. However, because of potential durability issues with grouted tendons, some highway agencies recently opted to use ungrouted tendons for post-tensioning to facilitate replacement. Combinations of bonded and unbonded tendons, as well as internal and external tendons or combinations thereof, are used for such applications.
The LRFD [Load and Resistance Factor Design] Bridge Design Specifications (referred to herein as LRFD BDS) addresses the design of post-tensioned concrete bridge elements (AASHTO 2020). However, some design aspects pertaining to this variety of tendon applications are not adequately addressed or evaluated (e.g., shear and torsion for elements post-tensioned with unbonded internal tendons, combined unbonded internal and external tendons, or combined bonded and unbonded tendons; and shear and flexure for elements post-tensioned with combined bonded and unbonded tendons). Research is needed to review available information, perform necessary analytical and experimental evaluations, and propose revisions to the LRFD BDS and LRFD Bridge Construction Specifications [(AASHTO 2017a) referred to herein as LRFD BCS], if necessary. These revisions will ensure appropriate consideration of the effects of tendon configuration on the design of post-tensioned concrete bridge elements.
1.2 Objective
The objective of this research is to propose revisions to (1) the LRFD BDS design procedures for post-tensioned concrete bridge elements with unbonded tendons or a combination of bonded (pretensioned or post-tensioned) and unbonded tendons; and (2) the LRFD BCS as needed. The research shall address both internal and external tendons.
