F1554 Anchor Bolt: how to design for tension + shear? 2

[hippo11]

I am having trouble finding how to design an F1554 anchor bolt, about 18" long, for tension and shear.

There is plenty of info for A325 and A490 bolts in Section J3.7 of the LRFD, but nothing for F1554...and according to the AISC (April 2002 MSC Steel Quiz) F1554 is the appropriate grade for anchor bolts > 9.5" long...NOT A325 or A490.

Can anyone help?

 

[Lion06]

Hippo-
I don't have the 3rd edition LRFD, but J3.7 in the new 13th edition is also combined tension and shear in bolts. I wouldn't have a problem using the same formulas for anchor rods (F1554) as for bolts (A325 or A490).
As a simple conservative check, I might use fv/phiFv + ft/phiFt <1.0.
The equations in J3.7 allown full strength of shear or tension if the smaller of the two is less than 20% of the available strength.

 

[hippo11]

Thanks...but if I use the J3.7 formulas, I need to know what to use for the Fv and Ft capacities of F1554, which aren't given like they are for A325/A490.

 

[jike]

ASTM F1554 has 3 grades 36, 55 and 105. I prefer the design procedure published in AISC Engineering Journal, 2nd quarter 1983, "Design of Headed Anchor Bolts" by Shipp and Haininger. You might also check ACI 318-02, Appendix D.

 

[Lion06]

hippo-
Table 2-5 on page 2-41 in the 13th edition (I am sure there is a similar table in the 3rd edition LRFD) gives the ultimate tensile stress for ASTM F1554 as 58-80 ksi. Using this information in conjuction with Table J3.2, I would use phiFt=0.75Fu*(Area of rod)=43.5*(area of rod); and
phiFv=0.40Fu*(Area of rod)=23.2*(area of rod).

 

[nutte]

This is why AISC calls them "anchor rods" instead of "anchor bolts," to keep you from using bolt equations on them. You should really be using the ACI appendix (which is awful), or the AISC Design Guide 1 for base plates, or one of the other references mentioned.

 

[UcfSE]

I agree with using the ACI appendix. I believe the PCI design handbook 6^th edition has some new information in it also.

 

[WillisV]

There is a lot of confusion on this - let me try to clear it up.

Anchor rods (yes correct terminology is rods) should be designed for both steel and concrete limit states.

AISC provides methods for the steel component, and ACI provides methods for both the steel component and the concrete component. The steel design component of ACI and AISC differ from each other in methodology but end up with approximately the same answers.

As an example take a 3/4" diameter, F1554 Gr36 rod in tension:

AISC Method: As Structural EIT described, per J9 (referencing the 13th ed manual) the anchor rods should be designed as threaded parts per table J3.2. Per table J3.2, for threaded rods Fnt = 0.75Fu. Per Table 2-5, Fu (min) = 58ksi. Per equation J3-1, Rn = FnAb where Ab is the full cross-sectional area of the bolt. So for LRFD, PhiRn = (Phi=0.75)*(Fnt=0.75*Fu=58)*(Ab=Pi(0.75^2)/4 = 14.4k.

ACI Method: Per Appendix D, the strength of a single anchor in tension, Nsa = Ase*Fu. Phi factors differ depending on if the anchor material is ductile or not, with ductile being defined as having a tensile elongation of 14% and reduction in area of at least 30% per the material ASTM standard. From the ASTM standard for F1554, Gr36 qualifies as ductile and gets a phi factor of 0.75. Ase is the EFFECTIVE cross sectional area of the rod (see commentary RD.5.1.2 in ACI Appendix D). It can be calculated per the commentary equation but is also available in Table 7-18 of the AISC 13th edition manual. For this bolt, Ase = 0.334. So the final tensile strength = (Phi=0.75)*(Ase = 0.334)*(Fu = 58ksi) = 14.53k.

So you are looking at 14.4k with the AISC method vs. 14.53k with the ACI method.

 

[Lion06]

Nutte and UcfSE-
Am I wrong in saying that the ACI appendix will only give you shear and tension values (and interactions) for the concrete breakout strengths, and not for the anchor rod?

Nutte-
The new base plate design guide #1 follows the same formula EXACTLY for tension and shear interaction in anchor rods as for bolts (as shown in equation J3-3a) in the 13th Edition steel manual. See AISC Design Guide #1 page 43 as a reference.

Hippo-
I would follow the design guide, but if you don't have access to it the formula for tension and shear interaction are identical as in the 13th edition on page 16.1-109 (Eq. J3-3a). I would get the Fv and Ft capacities as described above. Those capacities that I mentioned earlier are for loads, not stresses. For stresses, just use the phi=0.75 for tension and 0.4 for shear and a nominal stress of 58 ksi (unless you are specing a higher strength).

 

[nutte]

The ACI appendix also checks the steel anchor rod.

You're right about the AISC checks in the Design Guide 1. But when you go through the ACI appendix procedure, you'll end up checking them there as well.

A note of caution about using the AISC equations for anchor rods: You usually have super-oversized holes at base plates, so the plate might not engage the anchor rod in shear. You can resist shear through a shear lug, friction under the base plate, embedding the base plate in concrete, etc. You also often have a grout cushion between the concrete support and bottom of base plate, so if you are counting on the anchor rods to resist shear, you'll induce bending in the anchor rod. All of these issues are absent in steel-to-steel bolted connections, which the AISC equations are primarily intended for.

 

[WillisV]

StructuralEIT - yes ACI checks steel strengths - I did an example using ACI right above your post.

 

[Dinosaur]

I have used the approach indicated in the AASHTO Guide Spec for overhead signs, signals and luminares. This formula uses the square of the ratio of fa/Fa and fv/Fv if I recall. I uses the reduced threaded areas and I include bending stresses as a result of applied base shear when the anchor rod protrudes more than 1.5 x Bolt dia from the concrete. A little bigger bolt is cheap insurance against collapse as many of these connections are nonredundant.

Good Luck.

 

[minorchord2000]

nutte is right. you should be using the most unintelligable code every written, ACI Appendix D.

I hear from my spies that this appendix is a "work in progress" and that "big" changes are on the way. However, I would not wait for it soon.

It is way too tedious to use and I have reverted back to my old way of doing anchors.

 

[UcfSE]

It's not THAT bad, especially with a spreadsheet or mathcad.

 

[nutte]

I would say that it IS that bad, and even worse! I don't mean the tedious nature of the calculations and procedure (we're engineers, we can handle it). We have it programmed in Excel, and the results are often counter-intuitive, to the point that you know it can't be accurate. The most blatant example is how in certain cases, you can increase the embedment depth and get less pull-out capacity.

What irks me the most is that our anchor rods are always surrounded by rebar. This procedure neglects that, yet it's supposed to be the "best" method around. I hate it. If it's a "work in progress," they should have left it on the drawing board. It's the most backward procedure I've come across.

 

[PackerFan]

If you loads are decreasing as you increase the embedment, you may not be taking the adjusted embedment depth into consideration for situations were there are three or more close edges (usually in pier calculations). This new design method is the only anchoring code that has ever taken rebar into consideration.

 

[miecz]

Agree with Dinosaur that the AASHTO Spec for Highway Signs, etc. applies. Article 5.17.6.4 suggests bending to be considered when the clearance from the bottom of the leveling nut to the to of the concrete equals or exceeds one bolt diameter.

The bending moments are determined using a beam model fixed at the top of the concrete, and freee to displace but not rotate at the bottom of the leveling nut. For bending stresses, I use the root diameter of the thread, in lieu of the tensile stress diameter.

Finally, AASHTO recommends that the base plate be equal to or greater than the diameter of the bolts. Thinner base plates contribute dramatically to the bending moments in the anchor bolts.

 

[larryzim]

I can't pass by without a comment. In case you aren't aware, ACI 318 Appendix D is written for plain concrete, which is rarely used in structural engineering. In fact, it makes one wonder why they placed it in a code for reinforced concrete, rather than the plain concrete code. (I think they just wanted to share what they learned in their research.) For the more common anchor design in pedestals and other reinforced concrete, you need to apply the provisions of Chapter 12, using Appendix D (or ACI 349 Appendix B) to determine failure planes that need to be reinforced. Hope this helps.

 

[Lion06]

Since this thread has seemingly taken on a different life, I have two questions.

larryzim-
What you say makes sense, but where exactly does it say that appendix D is for unreinforced concrete? I can't find that anywhere.

All-
D.2.2 says that this applies to cast-in anchors AND post-installed anchors. Then it also says that specialty inserts, adhesive and grouted anchors are not included. What kind of post-installed anchor is NOT a specialty insert, or and adhesive or grouted anchor?
This statement also leads me to the conclusion that hilti and powers values are to be used from their catalogs and NOT to investigate their capacities via appendix D.

Any comments?

 

[dik]

Any literature I've seen suggests that shear and tension be combined since shear is often resisted by shear friction which often translates into tension...

Dik