Concrete embedded bolt pullout strength

[HankVRSI]

For years I have used a procedure in CONCRETE INTERNATIONAL dated July 1981 titled “Guide to the Design of Anchor Bolts and Other Steel Embedments” which outlines how to calculate the concrete pullout strength of embedded bolts in concrete. The procedure basically uses the tension strength of the concrete applied to the surface area of a 45 degree cone that has a height measured from the top of the embedded bolt head to the top of the concrete. This gives a formula based on the height squared. The ACI code has recently added an Appendix D which goes into detail regarding bolts embedded in concrete. The basic pullout value for a single bolt is stated in formula (D-7). The constants in the formulas for the different methods are very similar except in the first, the height is squared and in the second the height is raised to the power of 1.5. Unless I am missing something, the resultant pullout strength is considerably different, especially as the embedment depth becomes larger. For this reason, many of the standard foundations I have designed will no longer pass the requirements of the latest ACI 318 code. Does anyone have any comments or suggestions?

 

[WillisV]

You are correct, ACI Appendix D is required for concrete embedment checks as of its inclusion explicitly in IBC 2000 and by reference in IBC 2003. Compared to older methods it is much more conservative, especially in larger embedments.

 

[jheidt2543]

The 45 degree angle came about from 1980's reseach at the University of Stuttgart that resulted in the Kappa K)method of designing anchor bolts. Appendix D is based on a large international research project carried out in the 1990's. One of the big differences is that the 45 degree angle is no longer used, the research showed it to be like 35 degrees.

A very good reference is Chapter 34 Anchoring to Concrete in the PCA's publication "Notes on ACI 318-02 Building Code Requirements for Structural Concrete". It is well worth the price.

 

[HankVRSI]

Thanks to both of you for replying to this thread. Your input has been helpful

 

[theonlynamenottaken]

I don't know about the PCA publication that jheidt2543 referred to, but I do have PCA's "Strength Design of Anchorage to Concrete". Do not waste money on this publication unless you DON'T own an ACI 318 with Appdx. D. This PCA publication was almost word for word adopted by ACI as the new Appdx D.

 

[epr]

HankVRSI,
I don't know if you need be overly concerned about your previous projects. The anchorage analyses and the requirements spelled out in Appendix D are for plain concrete. Most of my foundations, especially those with piers, have confining reinforcing that penetrates the shear cone and adds to the pull-out strength of longer anchors.

A very good reference for this analysis (which is allowed per ACI 318, section D.4.2.1) is Structure Magazine, July 2004, in an article entitled "Alternatives to ACI 318-02, Appendix D - "Anchoring to Concrete"".

 

[structuresguy]

Actually, there are correction factors which account for the reinforcing cage in Appendix D. I don't have my ACI here, so I can't confirm which paragraphs they are located in. I think it is possibly the Class rating, Class A is unreinforced, and Class B is reinforced. Could be wrong on that, working from memory. There are also correction factors for cracked vs uncracked in service. These are interesting to me as I design many tilt panel buildings with bolted in place bar joist seats (bolted in place when the contractor misses the embed location). Since I design my panels by the tilt panel method, which limits by flexural tension, I have to assume that the panel is cracked in service if the location in question is at a moderate or high momemt region.

Does anyone know of a software program which calculates pullout and shear based on ACI318-02 App D??? I really hate to spend the time writing an Excel spreadsheet if I can buy a simple utility.

Thanks

 

[HankVRSI]

epr I could not find your reference in the archives of Structure Magazine for that month. Could it have been a different month?

Thanks for the reminder about this magazine. I had forgotten that it existed as I am in a specialized area of structural engineering. Interestingly I could not find how to subscribe to this magazine at the website. I assume it comes with a membership to the organization but have sent an email for the information regarding the subscription.

 

[HankVRSI]

epr I am not concerned about my previous projects as they have withstood the test of time so to speak. However my company has several “standard” foundations that support “standard” structures which now do not meet the ACI code. I now have to inform my managers that the foundation is no longer adequate and must be changed. They have a hard time understanding the necessity of the changes.

 

[epr]

HankVRSI,
The article is deinitely in July 2004. It is actually under the column heading "from experience", on pp 39 and 40.
Structure is available as a specialty magazine from ASCE.

 

[HankVRSI]

Found the article and got information on the magazine.

Thanks