Coulmn Design with Axial Load and Moment at Base Plate

[aswierski]

I am analyzing single column, unbraced pipe supports using ASD05 (although LRFD is acceptable as well) and have a question regarding the column design. I've used the methods prescribed in Salmon & Johnson's "Steel Structures" (5th Ed.) for axially loaded columns. As you can see from my attached calc, this obviously does not account for the moment I have at the base plate. Even though it is not shown as such, assume all of the loads to be already factored.

My question is this: How do I take the moment into account? I know I should be designing this column as a beam-column, but Salmon & Johnson only give examples for W-shape columns. Per our clients standards, we can only use HSS members. Can anyone give me some advice on this? Or point me in the right direction? Thanks in advance.

 

[msquared48]

I assume you are talking about the column itself and not the base connection.

The AISC Structural Steel code covers this for the column itself, unless you have biaxial bending. I assume not though from your sketch. That would be a different animal.

Where are you located?

Mike McCann
MMC Engineering

 

[aswierski]

I'm at my desk

 

[aswierski]

In New York... But this job site is in Indiana. It is inside a building, so now wind or snow loads apply. Sorry for the sarcasm. My Bills got spanked yesterday, rough day for me...

 

[msquared48]

No worries. I needed a laugh after this weekend. Thanks.

Mike McCann
MMC Engineering

 

[ishvaaag]

http://www.steeltools.org/STEELTOOL...umentKey=e3014764-aa27-45f6-96f2-111fe0863933

Here you will find some Mathcad worksheets able to check and optimize your pipe beamcolum according to AISC LRFD 1993 flavor.

Have also worksheets for baseplate design but lack the generality required to be used without a bit of engineering judgement, so I have not posted them at steeltools. Whilst the best advice is to follow the design guide for baseplates by AISC.

 

[aswierski]

Unfortunately, I do not have MathCAD.

 

[ishvaaag]

Hmm there is I think an Excel sheet as well there that does... let's see

this others seems to work and it is AISC 13 (but it says ASD). Anyway...

http://www.steeltools.org/STEELTOOL...umentKey=8458c9f5-b4e3-4836-82b8-c297f1f18611

 

[Stillerz]

not sure what the question is here....aren't we just talking about a member subject to combined forces...covered in chapter H of AISC 13?

I have to assume you have a moment baseplate connection.

 

[Stillerz]

Mike-
What would bi-axial bending matter? Without looking in great detail, I am pretty damn sure Chapter H covers this situation.

 

[Stillerz]

there is a CD with examples that comes with the AISC 2005. See examples H.1a, H.1b, and H.2.

 

[sandman21]

You need to check the column for the combined effects per Chapter H. Then check the base plate for the moment.

 

[aswierski]

Ok guys, thanks for all the guidance so far. My problem, though, is that all of the examples I've found are for W-shapes and/or braced frames. Technically this isn't a frame, and I'm restricted to using HSS members as columns. I will read through Chapter H tonight in addition to S&J's chapter 12 commentary.

ishvaaag,

The spreadsheet you posted is great. It is exactly what I need to do my analysis/design. However, I still want/need to learn how to do this by hand so I can better understand the concept.

I will do some research tonight and post back sometime in the morning with some updated calcs. Thanks again, gang.

 

[Stillerz]

asweirski-

This shouldn't be to difficult at all, just apply chapter H. In fact, it is probably going to just be a matter of looking up design strengths from tables and using the interaction equations of chapter H. Fear not the HSS!!! You dont need an exact example as in the case of your W-shape design.

 

[JAE]

As others have said - go to Chapter H (I'm just repeating good advice above).

 

[aswierski]

Ok, I'm all set. Chapter H has everything I need. Thanks guys.