Loose Lintel Design 3

[KootK]

I'd like some information on how to design a loose lintel using a single steel angle. By loose lintel, I mean the headers that often frame over doors and windows to carry portions of the masonry facade above. It seems odd that there is little information on the design of these members when it is such a frequently used application.

All I've been able do dig up as far as design examples are vague rules of thumb and prescriptive deflection requirements. I realize that there is an AISC spec for the design of single angle members. The problem for me is, since these lintels are laterally unsupported (I think), a lateral force of about 60% of the vertical load will go into the masonry.

How can I account for this effect in the masorny? Also how should bearing be addressed at the lintel ends? And how should I determine the capacity of the masonry wall below to carry the lintel reactions? I'd really like to have some kind of refernce on this with explicit design examples. Any assistance that you could provide would be greatly appreciated. Thanks.

Adam

 

[LPPE]

Typically, loose lintle spans are rather small, therefore, not a large angle is required. Also, if there is enough masonry above, you get an arching effect of the masonry, and the lintle loads become rather small. A typical lintel for a door opening in 4" veneer is L3 1/2x5x5/16 LLV. And thats overkill. (Galvanized, of course). As for bearing, usually you can just bear the lintel on the masonry veneer. Its not much different than that bottom brick supporting hundreds above it.
For other lintels, I would design them just as you would for a beam.

 

[ishvaaag]

http://www.bia.org/html/frmset_thnt.htm

download lintels which is the pdf item 31B

Since form the professional association, must be practical enough as to prevent most acknowledgeable failures.

FOr more you need to deepen in your stated issues, true.

 

[KootK]

Here's what I got when I posed this question to the AISC tech department. Apparently nobody has an anylitical procedure for designing these. I guess I should just relax and go with the rules of thumb.

Adam:

There are no specific AISC criteria for your design.

After speaking with another engineer in our department (who used to design these lintels), I think that there are at least three things that you should consider in your design:

1. Chapter F of the Specifications. This is the chapter on flexure.
2. Bracing. You may need to add bracing, and we agree that the blocks do not provide this bracing.
3. If your engineering judgment tells you that the flanges may be loaded beyond their capacity, you could treat the flanges (or angle legs) as a cantilevered beam (assuming a distributed load) to check whether they can handle the load. If your load is not distributed evenly across the flanges, a finite element analysis may be necessary.

Regards,

Sergio Zoruba, Ph.D.
AISC Solutions Center

 

[structuraleng]

AdamP,
I too had difficulty trying to find some design guides for loose single angle. I think this is the best that you could do or at least all that I could come up with, either way it is a pain:

You may have to use these references in combination.

Safe Load for Laterally Unsupported Angles - by Leigh, Thomas, and Lay (First Quarter 1984 Engineering Journal).

PCI Design Handbook 5th Ed. P. 6.20.

Salmon and Johnson - Steel Structures 3rd Ed. (The sample problem in here is kind of a pain to work out, but I think it's the best.)

Let me know if you can not find any of the above references.

 

[KootK]

Hey Structuraleng!

The only one of the references you mentioned that I have available to me is the Salmon & Johnson (and I'm not sure which example you're refering to--it's a big book!).

I have actually gotten some useful information regarding single angle design that I could share w/you too.

Adam

 

[structuraleng]

The example in Salmon & Johnson is on p. 436. If you want, I can fax the other references to you.

 

[KootK]

I found the Salmon & Johnson example. Thanks. If your could fax me the other References too, that would be fantastic. My fax No. is 509.275.6364. Send attention "Adam Pearson". Thanks again!

 

[structuraleng]

AdamP,
I've faxed you the references above. Perhaps you can go to

http://www.buildabout.com

and answer some questions on that forum. Keep me posted on your progress.