Splicing Anchor bolts with pier Reinf?

[BurgoEng]

I have looked on this site and almost found my answer but it was completely discussed. I'm sure there is a way to justify how uplift load would transfer from an anchor bolt into the reinf of a pier, but I am not sure how to go about figuring it out.

My particular situation is that my pier is limited to 12"x12", with 3/4"dia AB's and 20k uplift. According to my ACI App D calc, I only get a capacity of pull-out, roughly 11k. Someone had mentioned to me that you could lengthen the bolts to act as a splice connection to the pier reinf, but neither of us were sure how to determine that length, considering the different steel grades (36ksi bolt, 60ksi reinf)

Anyone know?

 

[PackerFan]

App. D uses a 35 degree angle cone for the breakout capacity, use this to figure out where the cone will intersect the rebar in the pier. Then, make sure the rebar extends the lap length beyond the intersection.

 

[BurgoEng]

So you saying.... if my reinf is 3" from my bolt, then the "cone" intersects the reinf about 2.1" above the bottom of the bolt. So, I simply have to have the required lap/splice/development length below this intersection point?

Or, in other words, the length of reinf needs to be equal to development length + 2.1" beyond bottom of the bolt?

 

[SteelMover]

The rebar needs to be developed where the crack crosses the rebar. So Your embed depth is Ld +2.1"

To shorten your embed length you can also develop your rebar faster by using 180deg bends, 90 deg hooks, or they make mechanical heads that attach to the end of the rebar to fully develop it over the length of the head, like a stud end.

Check out the link for more:

http://www.erico.com/public/library/Concrete/LT0434.pdf

 

[SteelMover]

Oh yeah, don't forget that you have a fully cracked section so you need enough rebar for the full 20k. Keep your crack widths to a minimum by providing extra anchorage if this is underground or corrosive.

 

[DaveAtkins]

And remember that rebar always needs to be developed on BOTH sides of a plane of failure--so the rebar needs to be developed above the intersection point as well.

DaveAtkins

 

[jike]

Calculate the development length of the pier reinforcing and then multiply by 1.3 for the lap length. Proportion that length down (normally the capacity of the pier reinf is greater than the anchor bolts)by the ratio of the anchor bolt capacity to the rebar capacity. The embedment of the anchor bolts then should be that reduced length plus the horizontal distance between the rebar and anchor bolt plus 2". (The 2" is the clear distance of the rebar to the top of pier). This assumes that the anchor bolt is fully developed by a heavy hex nut or head on the bottom.

Note that if there is shear on that same connection, you need to increase the tension in the anchor bolts to account for shear friction.

I hope this helps!

PS Check out the article about anchor bolts in AISC Engineering Journal, 2nd quarter 1983 by Shipp and Haniniger.

 

[miecz]

See the article on page 39 in the July 2004 issue of Structure Magazine.

 

[dik]

The AISC has a publication on the design of anchor bolts and the length of development of the pier reinforcing steel is dependent on the proximity of the anchor rod to the vertical pier reinforcing.

Dik