broken strands

huangyhg

broken strands
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?
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
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.