Single Angle Columns

[krus1972]

I am using Enercalc to check the capacity of a single angle
to be used at a lightly loaded column.

After selecting the proper angle Enercalc immediatly replies with "Single Angle not Allowed"

If the minmum KL/r = 200 is met and you can get the capacity Fa, I do not see why a single angle cannot be used as a lightly loaded column. Is there an AISC ASD provision that prohibits the use of Single Angles to be used as a lightly loaded column or is Enercalc not correct?

Thanks,

Jeff

 

[aggman]

Single angles are used all the time for lightly loaded columns, particularly in industrial applications. Just make sure that you are accounting for all eccentricities and follow AISC's Design of Single Angle members pg 5-309 of ASD 9th edition. The example calculations on pg. 3-55 - 3-58 are useful in understanding what must be considered.

 

[aggman]

By the way I don't use Enercalc so I don't know what or why its telling you "single angle not allowed". I would warn you that we are typically somewhat conservative with single angle columns just to be on the safe side with them.

 

[oth1]

AISC allows the use of single angles as beam and columns, however, the check is more complicated than for other shapes, see the AISC spec included in the green handbook on page 5-309 also see some worked examples starting on page 3-55. The LRFD version of the spec is available for free download from AISC at ...

http://www.aisc.org/ContentManagement/ContentDisplay.cfm?ContentID=4208

 

[mrMikee]

krus1972,

Here's another discussion with info on single angle columns that might be useful. My guess is that your program doesn’t get into the complexities of single angle struts.

thread507-131758

In short, the problem is that an angles major and minor axis are not the x and y axes. An axial load that is not thru the cg (and most of the time they aren't) will cause bending that needs to be transformed to the z and w-axes. This is tedious process considering the relatively complicated allowable stress formulas. In addition to the section in the ASD that aggman suggests you should also check out pages 3-55 thru 58 for two examples.

It was mentioned in the other thread that the new combined spec has changed concerning single angles. I'm not sure exactly how at this point, so if you are interested check it out.

http://www.aisc.org/2005spec.

Regards,
-Mike

 

[mrMikee]

Now that I have read thru the posts again, I notice that both aggman and oth1 did mention the examples on page 3-55.

Oops.

Just a momentary lapse of reason.

-Mike

 

[14159]

Look at the new AISC Specification which is a free download. It includes updated information for single angles. One key issue is that many of those weird eccentricities can be ignored in many cases. So much for the new Spec being all bad!!!

14159

 

[bjb]

There is an article in the AISC engineering journal from the second quarter of 1991 by Wayne Walker that has tables for allowable column loads for single angles. To use it your eccentricites should be about the same. For unequal angles, there is an article from the third quarter of 2001 that gives DESIGN STRENGTH for unequal angles, by Sherief S. Sakala. For rough estimating purposes when using allowable stress design, I have found that if you take the allowable compression stress based on the Z axis and divide by 3, you get something that is in the ballpark for equal angles. Again, that approximation is only for rough estimating. When I use a single angle column (which is rare), I use the tables above and detail so my eccentricties match the assumptions. You can get these articles from the AISC website, for a fee, but they're free if you're a member.

 

[mrMikee]

The new combined spec has some different assumptions for single angles. Would it be advisable to use the logic of the new spec with the old ASD?

Has anyone noticed whether the old ASD is still acceptable in the new IBC 2006?

I'm just trying to hang on a little longer.

Regards,
-Mike

 

[bjb]

That's a good point. I think you can still legally use the old spec until your building code recognizes the new one. In my state we're still 2000 IBC so I can still use it. On the other hand, we know that the old spec has a proven record of safety, so from a purely engineering standpoint, I wouldn't have a problem using the referenced journal article.

 

[transmissiontowers]

It is probably huge overkill, but I use GTStrudl and it has the capacity to do a buckling analysis of a FEA plate element model. I have seen a wideflange modelled up as a bunch of plate elements and loaded up with an axial load and the program will give the buckling factor for the member. You could do the same with a single angle. If you want a simpler solution, check out ASCE 10 which has formulas for single angles in compression.

_____________________________________
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