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 AASHTO LRFD Bridge Design Specifications address the design of post-tensioned concrete bridge elements. 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 was needed to review available information, perform necessary analytical and experimental evaluations, and propose revisions to the AASHTO LRFD Bridge Design Specifications and the AASHTO LRFD Bridge Construction Specifications, if necessary. These revisions will ensure appropriate consideration of the effects of tendon configuration on the design of post-tensioned concrete bridge elements.
OBJECTIVE: The objective of this research was to propose revisions to (1) the AASHTO LRFD Bridge Design Specifications design procedures for post-tensioned concrete bridge elements with unbonded tendons or a combination of bonded (pretensioned or post-tensioned) and unbonded tendons (both internal and external tendons), and (2) the AASHTO LRFD Bridge Construction Specifications as needed.
STATUS: Research is complete. The final report (without appendices) will be published as NCHRP Research Report 1139 and the appendices will be available as NCHRP Web-Only Document 417.
