RISA - Column Axial Results 2

[tft2001]

I have a simple question concerning the results of RISA analysis as follows. I have a single story framing system and the axial load between the top of the column and the bottom of the column is consistently 3.245 kips; however, my column only weighs .431 kips and there are no other additional loads being applied along the length of the column. Any thoughts?

 

[msquared48]

I assume your question is "Why is the difference between the top and bottom not .431 kips?"?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[WWTEng]

Double check your load cases, you may have loads applied. Also take a look at load combination, you may have a factor much larger then 1 in your load combination under your dead/self load case.

 

[BAretired]

My guess is that you added the column weight to the top node of the column which, by the way, is what I would have done.

BA

 

[steellion]

It could be from P-delta effects.

 

[JLNJ]

That may be the RISA default for self-weight. I'm guessing Josh will be along shortly to confirm.

You could play around with a small model and see what results you get. You might answer your own question.

 

[JoshPlumSE]

If you're not seeing a change in the axial force of that column then you are probably not including self weight in your analysis.

RISA does not include self weight automatically. Normally, you want to create a seperate basic load case where you set the Y gravity entry (if that's the vertical direction) to -1. If you do that, then the program will include self weight whenever you include that load case in one of your load combinations.

 

[weab]

Do you have perhaps X-bracing? Depending on your other loads, diagonals might apply axial loads.

 

[PMR06]

You must be picking up load from whatever is framing into the top of that column. Check the end forces of the members framing into the top of that column. Even if its a braced bay, break the brace axial load into the correct vector. The load is coming from somewhere...

 

[msquared48]

Josh has it.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com