Pretensioned Anchor Rods into Concrete Pier 1

[efFeb]

Good Morning,
I am trying to wrap my head around pre-tensioned anchor rods; I have read a number of other threads and am still not quite there.
If I have an anchor rod pretensioned to 1500kN, and this is anchored into a concrete pier, does this add a 1500kN compression force to the concrete pier? If I then apply a 1000kN tension force to the rod, does this then mean that there is no tension force actually seen by the concrete pier?
Thanks very much in advance for your help

 

[HTURKAK]

My responds would be ;

R= The answer is yes . The concrete portion of the pier btw anchor plate and the nut will be compressed with 1500kN compression force. ( if we neglect prestressing losses such as relaxation due to the creep ..) However , the stress distribution is another story.

R= True ..provided that the prestressing force available at the rod still more than zzero.

Pls look to the following doc. for anchor design and prestressed anchor.

https://tuxdoc.com/download/sabp-q-001-anchor-bolt_pdf

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[KootK]

If I have an anchor rod pretensioned to 1500kN, and this is anchored into a concrete pier, does this add a 1500kN compression force to the concrete pier?

No, not in the global sense. The compression at the anchor head is imagined to strut it's way up to the base plate without inducing a breakout frustum in tension. I'm a bit skeptical that is the case once poisson ratio etc are considered but, then, I tend to be skeptical about a lot of things.

If I then apply a 1000kN tension force to the rod, does this then mean that there is no tension force actually seen by the concrete pier?

Yes, again in the global sense. The idea with anchor prestressing is usually simply to prevent anchor fatigue fracture by controlling the stress range experienced by the anchor rod.

You do need to consider concrete creep relieving the anchor pretension as well as provisions (sleeving, chairs etc) for appropriate anchor stretch length.

You may find this little blurb by the Williams anchor folks helpful: Link

 

[KootK]

This is good too: Link