On rare occasions, the ironworker/installer will need to detension an already-stressed post tensioning tendon. The reason may be due to a repair procedure or re-stressing due to out-of-range elongation readings.
- During the detensioning process, the post-tensioning tendon will have to be “over-stressed.” The PTI Field Manual recommends that the hydraulic jack and pump gauge pressure should not be taken more than 5% over the normal stressing gauge pressure (at 33 kips of 0.5? tendon).
- The jack should be opened at least 4 inches so that it does not get “hung up” in case the wedges fail.
- The detensioning procedure be performed shortly after the normal stressing operation. Over time, the wedges deformed inside the anchor cavity and form a “lock” with the strand and anchor. (Refer to the PTI Field Manual 3rd Edition section 10.9).
The pictures below show an example of how to detension the tendons with a Detensioning Tool.
Failure to use the proper parts or equipment could result in damaging the anchor, strand, equipment or harming the operator/by-standers. This procedure should be carried out by a Post-Tensioning Institute Certified Ironworker (level 2). This post is not a complete procedure for detensioning PT tendons. Proper jobsite precautions should be taken to restrict personnel during stressing and detensioning processes.
– Neel Khosa, Vice President, AMSYSCO
Copyright © 2011 by AMSYSCO, Inc. All rights reserved.