Broken Strands

[11822]

Background:

-Cast in-situ viaduct, spans ~42m
-3 webs
-6 anchorage in a web
-31 strands in an anchorage
(all fixed at one end, ~12mm dia. each)
-Day 1, stress to 50% design stress for all anchorages

-Day 2, 5 strands in an anchorage were broken while stressing

Any suggestions to this issue?
What the redundancy in strands design(ie 20% or 40%) usually?
What are the measures to rectify the situation?

 

[Zambo]

If only one strand and it has pulled out of the anchorage wedges you might be OK. But 5 strands broken and it's not even known why they broke, I cannot see anyone accepting the tendon as a whole.

I guess you have to de-stress and replace the tendon.

Zambo

 

[flamby]

11822,

I had a similar disaster to start the year'04. Our fabricator wished me happy new year with the news about a pressure vessel item, designed by me, he was fabricating. At 50% load, during testing, a bolt just snapped into two.

Reason was found later. The guys did not torque this bolt with torque-wrench to specified value, but used their Horse Sense and Hammer. It was over overstressed and taking the load in undue proportion.

Always see that post-tension is applied uniformly and equally. Use Instrumentation, if necessary.