Walsh and Kurama 2008
The authors discuss the results of an experimental study on the behavior and design of anchorages for unbonded PT strands in seismic regions. Single strand/anchorage systems were subjected to monotonic tension loading, considering various design and construction parameters which could affect the performance of a strand inside an anchor. The primary purpose of this research was to investigate the ultimate strength and strain capacity of different strand configurations while developing guidelines for testing and design. Therefore different strand samples were tested and strand stress and strain data, elapsed time, applied load, crosshead displacement, and strand elongation were recorded.
System Concept
This structure is composed of unbounded PT tendons, PT anchors, and concrete. High strength PT tendons were used between precast beam column and wall members to provide lateral resistance under seismic loading. The gaps at the joints between structural members govern the lateral displacements of the structure. Use of the unbonded tendons is intended to reduce concrete cracking and delay the yielding of the strand. Moreover, this structure offers self-centering capability through the PT force. These kinds of unbonded PT strands yield a wide variety of applications and could be used in frames, shear walls and coupled walls.
Experimental Study, Results, and Discussion
Cast anchors, barrel anchors, and anchor wedges seven wire strands were tested in this study. The dimensions and properties of the anchors were varied. From test results; the maximum stress and strain capacity of the strands is controlled by the fracture of individual strand wire inside the anchor wedges. Moreover, the strand wire fractures resulted in a reduction in the self-centering capability of the subassembly upon unloading as well as a reduction in the lateral stiffness of the structure during the subsequent loading cycles.
Ongoing Work
The authors plan to conduct a series of tests with the two ends of the strand specimens embedded in concrete blocks to develop more realistic strand strength. Tests on selected strand/anchorage systems under cyclic tensile loading conditions simulating a seismic event will also take place.
Reference
Walsh, K.Q. and Kurama, Y.C. (2008). “Behavior and Design of Anchorages for Unbounded Post Tensioning Strands In Seismic Regions,” Proceedings of the Structures Congress 2008, Vancouver, BC, Canada, April 24-28.