Permissible deviations of indirect reinforcement in anchorage zones of prestressed structures

Abstract

Regulatory standards for permissible deviations in anchorage zones of prestressed elements often fail to account for the dimensions of indirect reinforcement, the geometric parameters of anchors, or the actual loadbearing capacity of the zone transferring forces from the anchor to the concrete.
This article presents a case study on determining the permissible misalignment tolerance between spiral indirect reinforcement and the OS-55 (55-strand) cup-type anchor supplied by STS Ltd., a prestressing system provider. The anchor is used in the prestressing system of nuclear power plant (NPP) containment structures. Additionally, the study examines the permissible deviation of indirect reinforcement in the OS-19 (19-strand) anchor, commonly found in bridge structures. A real-world example of anchorage zone failure in a prestressed concrete beam from a civil engineering project is provided, demonstrating how excessive misalignment between the spiral reinforcement and anchor led to structural damage–highlighting the relevance of this research.
A review of domestic and international regulatory documents is presented. Finite element analyses were performed to evaluate load transfer zones from prestressing anchors to concrete under varying degrees of spiral reinforcement misalignment relative to the anchor axis.
Analysis and comparison of calculation results for the OS-55 anchorage zone, implemented in actual projects, showed that the permissible misalignment tolerance could be more than doubled compared to current regulatory limits. For the OS-19 anchorage zone, finite element analysis confirmed the permissible spiral displacement limits specified in standards. Any increase in this tolerance is only permissible if rigorously justified by additional verification.