Overprestressed Anchor Bolts Have Yielded, repair?
Overprestressed Anchor Bolts Have Yielded, repair?
(OP)
Pals
During pretensioning of high strength anchor bolts for a tall mast, 10% of the bolts found in base ring yielded.
Any other technique beside adding adhesive anchors?
respects
ijr
During pretensioning of high strength anchor bolts for a tall mast, 10% of the bolts found in base ring yielded.
Any other technique beside adding adhesive anchors?
respects
ijr





RE: Overprestressed Anchor Bolts Have Yielded, repair?
It would be interesting to know how you determined that some bolts yielded and others did not.
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
The anchors are cast in place.
The anchors have a strong bearing mechanism at their lower tips and have been greased to prevent bond.
Some hydraulic equipment used to provide some preloading force was not adjusted correctly when some bolts were being worked on.
The machine records pressure(correlated to prestressing force) and also the elongation.
For the case where operators did not make correct adjustments, excessive pressure(hence prestress) as well as excessive elongation were recorded on the logs.
I wasnt at site and I am not familiar with this machine. This is what has been reported to me
Analysis shows that if these bolts are assumed nonexistent, remaining bolts will work fine with a few overloaded bolts closest to the weakest ones.
It would be nice to add more bolts. I was just thinking there was a way to bring them back to elastic state.
there is a fatigue issue too.
respects
ijr
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
how do you unload bolts that have almost reached yield strains? That is exactly what I am looking for
respects
ijr
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
you mean when we unload, some permanent strain will remain but later loading will produce linear strain increase? Like in the way we test materials for repeated loading?
But is the final strain after reloading acceptable?
respects
ijr
RE: Overprestressed Anchor Bolts Have Yielded, repair?
Dik
RE: Overprestressed Anchor Bolts Have Yielded, repair?
Obviously, the ordinary way to detension (and only if you plan to reuse) the bolts is to turn loose the nut, with everything it implies for a yielded bolt. Hence to drive again to the wanted state may be at best feasible, but no one would call this a standard installation. You may try anyway for what would be a more uniform setup of the pretension, since, anyway, if non-existent you have found the structure to meet what required. I unfortunately am not an expert of bolt technology and must not give advice on what would depend on geometry of the engagement, the level of force, the chemistry etc. Since you do not lose but a present unruly situation for another, and both look mechanically acceptable to you, you might decide more than anything to see the feasibility of loosing the nut, then put it back again, satisfying technical curiosity and always learning something. If I would be in such mindset I would try to learn from the experts on bolts what to expect. If not available or not caring, likely would accept the present state of affairs, you know there's something not as well as it should be, but at least stays "controlled" and "clean". After touching the nuts we might not have these niceties.
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
ishvaaag, being not an expert should not prevent you from commenting. When you are not an expert you are more likely to be more creative, and getting out of the box.
Yes,the RCSC guide supports this reuse, though it recommends a maximum of one reuse. I appreciate what hokie mentions: the ductility
My anchor bolts are indeed alloy steels.
respects
ijr
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?
RE: Overprestressed Anchor Bolts Have Yielded, repair?