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Shear/Tension capacity of rebar?

Shear/Tension capacity of rebar?

I think is this probably a stupid question, but I'll be damned if I can't figure it out or find it anywhere in my texts.  I think it would simply be As x fy.  But that seems too simple.  I guess maybe you need to multiply by a phi value as well...0.7, 0.8?

I am asking because I am trying to determine the pull out strength of a rebar grouted into rock, as well as the shear capacity of that same rebar, grouted into rock.  What about a bolt, threaded rod, etc...?  Same idea as rebar?

It's been a long week....

RE: Shear/Tension capacity of rebar?

It is shear, so the ultimate shear stress is not ASfy but 0.6fy, also I think there is a shear lag factor of 0.6, then you multiply it by phi.

Usually dowels are limited by bearing with the concrete rather than shear.

What is the situation?

RE: Shear/Tension capacity of rebar?

I would think the bond between the grout and the rebar and the grout and the rock would be the key.

Don Phillips

RE: Shear/Tension capacity of rebar?

There are simple interaction formulas for combined shear and tension in this type of situation.

My Ramset anchoring book gives this:

N*/Phi_Nu + V*/Phi_Vu < 1.2

There are non-linear interaction formulas too.

As noted by the other posters, you are unlikely to fail the bar.

RE: Shear/Tension capacity of rebar?

On page 5 of the 2006 Simpson Anchor catalog, there are notes for the allowable shear and tension capacity for rebar that they use.  You should be able to find the catalop online.

RE: Shear/Tension capacity of rebar?

The situation is a concrete retaining wall that is supported on rock and I am trying to justify decreasing the width of the foundation by tying into the rock with grouted rebar to take up tension loads caused by overturning moment and shear loads from sliding.  We have a detail showing #9@18oc with "kelgen gold" grout, but I can't find anything on kelgen, which makes me think it's a really old detail, and I'd lke to verify why #9's are ok.

But more than just that I am trying to learn how this actually works, and to find the "correct" way to determine these types of things.  I am somewhat of the loan structural engineer in my office and there isn't anyone in to discuss this kind of stuff with, so I am forced to figure it out on my own and it can be quite daunting at times.  Thank gooodness for the internet.

RE: Shear/Tension capacity of rebar?

I would use 0.6Fy for the shear yield of the rebar.  You may need some additional data to make sure your rock won't crush or spall before the rebar can reach yield.  

RE: Shear/Tension capacity of rebar?

I forgot yo mention, the 0.6 coefficient is not a safety factor.  You will need to apply a safety factor on top of the 0.6.

RE: Shear/Tension capacity of rebar?

For shear yield, I would "start" with 0.4Fy for Billet, A615-85.

I emphasize "start", since, as previously stated, this is a coeff, not a safety factor.  Also I am basing my "start" coefficient on AISC 9th 5-148, F4, which is for carbon steel, not for rebar.  To my knolwedge there is not a specification for shear in rebar.  Why?  I don't know!  Threrfore, if I were to do this, proceeding with caution, I would compare my results with that of mechanical fastener specification and design manual data.

So, to elaborate on the original question, how do mechanical fastener manufacturers, come up with shear values?  i.e. Powers Fasteners Specification and Design Manual, 5th edition p. 189.

RE: Shear/Tension capacity of rebar?

I think you need to design this according to ACI 318 Appendix D.

First, factor your shear forces to get your design shear, Vu.

Your resistance, is this case, will be limited by the steel shear strength and the pryout shrength of the anchor.

The steel strength, phiVs=phi*0.6*As*min(fu, 1.9fy)
for ASTM A615 Gr60 rebar/ phi=0.65,  fu=90 ksi,  fy=60ksi

Depending on your geometry, the shear strength could be limited by the pryout strength.  The "nominal pryout strength" in shear is governed by Eq D-28.  To get the pryout strength, To get the pryout strength, multiply the "nominal pryout strength" by the phi factor covered in article D4.4c.

RE: Shear/Tension capacity of rebar?

Anchoring into rock is rather speacialized work and you might want to contact "Williams" or another manufacturer that makes rock anchors.  Regardless of what the numbers say I would also do a pull test on a couple of installed anchors just to be sure the rock, grout & anchor are all working together as planned.

RE: Shear/Tension capacity of rebar?

4wilmar is right. So, my earlier post applies to the required steel area and the embedment to the concrete footing, not the rock.

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