Testing Post-Tensioned Anchors
Testing Post-Tensioned Anchors
(OP)
The following is part of a Technical Memorandum:
"...water has intruded on the existing post-tensioning strand anchorages. The amount and degree of water present is unknown, but the presence of water can cause corrosion of the post-tensioned strand and anchor material.
If water is present, it is only a matter of time before the strength of the post-tensioning strands is compromised. If a post-tensioning strand fails, then the anchorage and structure associated with the strand may also fail. To minimise an untimely failure of the trunnion anchorage, remedial work should be undertaken.
Two approaches are prescribed. The post-tensioned anchorages can be 'proof loaded' on a regularly scheduled basis. When anchorages are identified with insufficient load capacity, then they should be replaced with the solid bar system noted earlier."
Is there a technical resource that has a prescribed manner and schedule for testing? I was thinking of taking the strands up to 1.25 times the 'real' design service loading, but less than 0.8 X fpu...
Any suggestions or comments?
Dik
"...water has intruded on the existing post-tensioning strand anchorages. The amount and degree of water present is unknown, but the presence of water can cause corrosion of the post-tensioned strand and anchor material.
If water is present, it is only a matter of time before the strength of the post-tensioning strands is compromised. If a post-tensioning strand fails, then the anchorage and structure associated with the strand may also fail. To minimise an untimely failure of the trunnion anchorage, remedial work should be undertaken.
Two approaches are prescribed. The post-tensioned anchorages can be 'proof loaded' on a regularly scheduled basis. When anchorages are identified with insufficient load capacity, then they should be replaced with the solid bar system noted earlier."
Is there a technical resource that has a prescribed manner and schedule for testing? I was thinking of taking the strands up to 1.25 times the 'real' design service loading, but less than 0.8 X fpu...
Any suggestions or comments?
Dik






RE: Testing Post-Tensioned Anchors
Are these ground anchors?
Are these post-tensioned strands through concrete?
Do the strands already have any corrosion protection? Grease and sheath? Grouted Encapsulation? Epoxy coating?
Are these bare, grouted strands?
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RE: Testing Post-Tensioned Anchors
Stretching it later to x1.25 service load could be great idea, as this, in conjunction with measuring the elongation, will give some indication of section losses.
RE: Testing Post-Tensioned Anchors
Dik
RE: Testing Post-Tensioned Anchors
Some of the early greases used in the post tensioned systems emulsified after only a few years, providing little or no corrosion protection to the cable. I recall one case in Calgary where strands in an apartment slab were said to be lashing out of the floor when the cable broke. One lady was exercising in front of the TV, went away for a few minutes and a cable ripped up out of the floor in the exact spot where she had been exercising. So much for exercising that day.
BA
RE: Testing Post-Tensioned Anchors
www.PeirceEngineering.com
RE: Testing Post-Tensioned Anchors
In my limited experience, tendon/anchor emergence is a relatively rare event that typically only occurs when concrete cover is low. However, it can be dangerous when it happens. I have been involved in the destressing of hundreds of strands and it was rare to see a strand emerge from the slab upon destressing .... although there was that one time the contractor had uncovered a live set of anchorages .... and yes, the anchorage did fly quite far when destressed. I learned never to stand behind a stressing jack during testing (lift offs) and/or tensioning the new tendons.
I can't help with any insight on the proof loading. Once the wedges were set and the strand was trimmed, there was never enough length left for the stressing jack to grab onto for any retests.
RE: Testing Post-Tensioned Anchors
I've been in touch with Dywidag already and will be in contact with VSL after Easter... been using Dywidag for 40 years... neat product
thanks Dik