Design of Foundation for Steel Structures 1

[StrucEIT]

Hi All. I am working on a project that involves design of the foundation system for a steel frame building. The building itself has already been deisgned by a steel company.

I have an idea of work involved. However, I would really appreciate it if any of you could direct me to some references that would assist me.

Thanks a lot.

 

[SacreBleu]

I am not aware of any how-to-design books in that category. Usually, it is a simple matter of tabulating the reactions from the steel building manufacturers' calculations. Then, anchor bolts are selected to resist the shear and/or uplift. Foundations are designed to resist the downward gravity loads/uplift. The amount of foundation and floor slab to take as active for dead load resisting against uplift is a matter of some disagreement amongst different engineers (chuckle)

 

[vooter]

Principles of Foundation Design by Braja Das is a good book. If it's a metal buildng system, Newman's book Metal Building Systems has some good information.

 

[14159]

Do you have any supervisors or project managers that can give you OJT for foundation design? It's really not something that you can get from here.

There's no way that you'll go from what sounds like "I've never designed a foundation in my life -- please help." to being able to design it based on our advice.

DBD

 

[UcfSE]

Try this:

http://www.amazon.com/exec/obidos/A...9/sr=2-1/ref=pd_bbs_b_2_1/103-1081764-8229416

Metal Building Systems: Design and Specifications
by Alexander Newman
Hardcover: 576 pages
Publisher: McGraw-Hill Professional; 2 edition (November 28, 2003)
Language: English
ISBN: 0071402012
Product Dimensions: 9.6 x 7.3 x 1.8 inches
Shipping Weight: 2.6 pounds.

 

[UcfSE]

Though you'll get a lot of information in the book I showed above, it is not necessarily going to match the practice in your area. For instance, the book tells you never to found a metal building on a thickened-edge footing but around here that's all anyone will do. Also, you may be able to find some preliminary reactions from the book but ALWAYS get the final reactions from the manufacturer. Be very conservative when you assume reactions, you don't want to have to increase the footing size after the fact.

 

[StrucEIT]

SacreBleu & vooter, thank you for your advice.

DBDavis, I do have a supervisor and he can guide me well enough for me to design this foundation system. However, I was just looking to see if there were any references that could help me accelerate my learning curve. I'm sorry if I offended you by my question. I wasn't looking to leech off you to finish this project. Thanks anyway.

Also, let me make my question a little less vague. I was told that we could use "hairpins" wrapped around the anchor bolts to account for the outward thrust from the frame. Could anyone please explain the basic action of these hairpins?

Thanks again.

 

[SacreBleu]

The hairpins are selected for 2 x cross sectional area tension capacity greater than outward thrust of the main load-bearing frames. Length of hairpin designed to develop the force in concrete.

 

[SacreBleu]

postscript - usually a single #4 or #5 bar "hairpin" works.

 

[strucsteel]

You may have to be somewhat careful about the detailing of the slab if you're counting on hairpins for resisting thrust. If you have true slab separation at control joints (discontinuous WWF or greased dowels), then you should probably only count on the hairpins pulling on the section of slab they're cast into when you're figuring your friction/cohesion sliding resistance. If you have a very long, low slope span with a very short eave height (100 ft span and 12 or 14 ft eave, ballpark), you may even have to run tie beams. They would be similar to hairpins in that the bars would be hooked around the anchor bolts, but the bars would be run continuous between the bases of each frame.

 

[Lutfi]

In PEMB slabs, it is strongly recommended that joint be placed in middle of the bay not at column/frame centerlines. This is done for various and obvious reasons.

Regards,
Lutfi

 

[mrengineer]

See thread 507-84403 for much more discussion on dealing with thrust.

 

[structuraldan]

PCA notes on ACI 318 are helpful but I've found mistakes in the sample calcs in the past.

Foundation design basics: 1) determine geometry (done), 2) assess allowable soil bearing or get from a geotech, this will determine your system. 3) determine initial column support dimensions on gravity loads, then check uplift then shear. 4) design grade beams and slabs from loads and soil properties, as needed.
Hairpins shouldn't be relied on to resist base shear. Don't forget to check your anchor bolt reactions to ACI 318-02 Appendix D.

 

[SacreBleu]

structuraldan,
You are saying that PCA notes do not recommend hairpin dowels? If the bolts can transfer the shear to the slab, what keeps the slab from "tearing" out? Or is the slab bearing against the grade beam?

 

[structuraldan]

SacreBleu

PCA notes are a helpful reference for concrete design, but I'm not sure if they address hairpins.

I consider hairpins a matter of "good engineering practice" for continuity of force transfer, not needing a design calc. Adequate development of slab edge reinforcement and/or grade beams should accomplish the same thing. UcfSE also mentioned not using a slab (vs. a bigger footing) to resist column base shear, to avoid a tearout.

This also is in line with the (unfortunate) result of the ACI 02 update - use more concrete. With price and availability of each these days, I'm not sure how much it matters. Either way, I'm willing to bet a #4 with 8' long legs @ 45 degrees will do the job w/o calculation.