Behavior of unbonded posttensioning monostrand anchorage systems under monotonic tensile loading

Abstract

This paper presents an experimental study on the ultimate behavior of unbonded post-tensioning monostrand anchorage systems under monotonic tensile loading. New types of seismic precast concrete structural systems using unbonded post-tensioning have emerged in recent years. While unbonded post-tensioned gravity systems (for example, floor and roof slabs) are common throughout the United States, the use of this construction technique for seismic resistance can put the anchorage regions (where all of the post-tensioning forces are transferred from the strand to the structure) under extreme demands. Strand-wire fractures can occur inside the anchorages, limiting the lateral strength, stiffness, ductility, and self-centering capability of the structure. The research described in this paper focuses on the strand stresses and strains at wire fracture, considering the following design and configuration parameters: strand diameter, anchor type (cast-type and barrel-type anchors), number of anchor wedges (two-piece and three-piece wedges), presence of a binding ring around the wedges, and cast-anchor date code and metallurgical properties. The test results are used to make design recommendations and to evaluate strand/anchor configurations that may provide a better probability of reaching higher strand ductility. In addition, current industry requirements for the acceptance testing of post-tensioning monostrand anchorage systems are assessed.