Steel Angle Axial Capacity

[NewEngineerHere]

Hello Everyone,

I have a simple question about the allowable axial load (Compression) capcity of a steel angle.
I have a steel angle used as a brace ( so the load applied to it as column... axially) What is the maximum capcity?
the angle is 4x4x1/2 and its 6 ft long.

Thank you in advance

 

[KootK]

The AISC manual has some great tabulated values for this that account for the fact that the load is almost always applied eccentrically through a connection to one of the angle legs. It's a serious time saver. For the background theory:

1) AISC spec obviously and;
3) Google Trahair + Single angle.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[andriver]

See tables 4-11 and 4-12 in AISC manual. Or follow chapter E in the AISC manual to do the calculations yourself. Will depend on whether it is eccentrically loaded or not.

 

[NewEngineerHere]

Many thanks for Kootk and andriver for your replies. That's what I did, I went to AISC manual table 4-11 and took the ASD number for this angle. But one of the engineer works here told me my number is wrong and it should be half of the value. So, of course being a fresh graduate, I needed to hear a second openion.

 

[KootK]

Maybe your colleague was under the impression that you were looking at the double angle tables. Although, half that value would still be wrong. Senior people tend to make quick assumptions and listen poorly when dealing with juniors I'm afraid.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[andriver]

First, you need to determine if its is concentrically loaded or eccentrically loaded.

Also, the tables are for 36 ksi steel, would need to make sure your material matches.

But, the left column corresponds to KL not just L, I'm assuming you used a KL = 6 ft but you need to determine what your K is. If he gets half of what you got, I bet he is using a K=2.0 which corresponds to a buckling shape e or f. See table C-C2.2 (AISC 13th pg 240).

 

[NewEngineerHere]

KootK, I also believe this is the case as well.

Andriver, I also looked into that, but the angle is simply supported by bolt connection at both ends so k value should be equal 1.0 (if I am correct...) So I used KL=6.0.
The angle is connected to beams flanges at each end at different elevation. The load is applied to the angle by jamb connected to a beam flange and the angle is connected directly at the jamb location.
I will also run hand calculation and read the referece Kootk suggested for my own understanding...

Thanks alot

 

[Hokie93]

Additional, useful references for design of single angle members are:
1.) Guide to Stability Design Criteria for Metal Structures, 6th edition (Chapter 11)
2.) Single Angle Design Manual by Whitney McNulty, P.E.
3.) Various AISC Engineering Journal papers (free downloads for members at

http://www.aisc.org)

 

[JStructsteel]

Why not just ask him why its half? If you dont agree then, you can discuss.

 

[wannabeSE]

NewEngineerHere,

If the connection eccentrically loads the angles (bolted connection through one leg), Table 4-12 should be used. This may be the table that the senior engineer is using.

 

[NewEngineerHere]

Thank you Hokie93 for these information. I will study them.

WannabeSE;
You are correct, thats what he later told me was using, also was using an older edition of AISC so when I was searching for his number I could not see it anywhere in my 14th Ed. AISC.

Would you please tell me what is the best way to know when to use either tables 4-11 or 4-12 ? Is it mainally by the connection detail ?

Many thanks everyone

 

[KootK]

Is it mainally by the connection detail ?

It is. You're essentially just giving consideration to how the load is actually delivered to the angle.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.