Strength, Ductility, and Prestress Losses of Unbonded Post-Tensioning Strands in Self-Centering Structures

Unbonded post-tensioning strands have been employed in numerous research studies for precast concrete bridge piers to provide restoring force under seismic loading. When designing these systems, premature fracture of strands due to stress concentrations at anchorages and post-tensioning losses should be considered. Previous studies on unbonded strands between post-tensioning anchorages under cyclic loading are limited to 12.7-mm and 15.2-mm diameter strands and have been largely based on small-scale testing. Only a few of these studies reported post-tensioning losses. This research assessed the behavior of post-tensioning strands under cyclic loading to fill these gaps. The experimental program included 12.7-mm, 15.2-mm or 17.8-mm diameter, seven wire, 1860 MPa ultimate strength, low-relaxation strands between standard anchorage chucks. Stress-strain relationships and the anchorage wedge-seating of post-tensioning strands under cyclic loading were obtained. Post-tension losses were predicted based on the small-scale results and compared to the loss of a large-scale case study.