Steel Column Reinforcement

[cvandenham]

So I have a steel (A36) box column 3x3x3/16" it is 63" tall and will have a 3000lb load applied at the top perpendicularly (its for a guard rail). As of now the column is not strong enough and needs to be reinforced. I was treating it as a simple cantilever beam with the load on the end. This resulted in a max stress at the floor of 101.5 ksi. I was thinking of adding a brace from the floor to the middle of the column but I am having a hard time finding any resources explaining how to calculate the max load or stress the new reinforced column could handle. Any suggestions?

 

[bookowski]

If you add a brace to the mid-height of the post then your 'L' will be 1/2 your original L, since your moment is M = PL this means that your moment will be cut in 1/2 as well. Doesn't look like that is going to get what you need. Bigger post + brace maybe?

 

[BAretired]

Your box column should be roughly equivalent to HSS 6x6x3/16. The maximum stress is not 101.5 ksi with the loading you have described. Check your calculations.

BA

 

[paddingtongreen]

If your brace is in tension, the bottom of your post will be in compression as well as bending. If your brace is at 45^o to the post and hits at mid-height, this compression will be twice the applied load, making it 6000#. If your brace is in compression, the added force will be tension, and that will probably overload the base connection. If the brace hits lower, the added forces will be greater, if higher, they will be lighter.

See what a replacement would be.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[BAretired]

I misinterpreted your meaning. I thought you were boxing four angles 3x3x3/16 to form a 6x6 column. Please disregard my post.

BA

 

[slickdeals]

What code are you using and where do you get the 3000 lb load for a guard rail?

 

[cvandenham]

so this column is part of a machine so I'm not worried about any building code at the moment. I thought i'd post it in structural though as it is a statics problem.

They don't want to replace the column but obviously it can not handle the moment caused by 3000lbs at the free end. I could add another 3by3 column behind it and then a brace? Would that work out essentially to making it a 6 by 3 column?

 

[BAretired]

It would work if you weld them together adequately to develop the shear flow, but welding at rounded corners requires special welder qualification.

Why not add a C6x8.2 each side and cut them off where the existing shape can carry the load by itself?

BA

 

[TDIengineer]

HSS6x3x3/16: Zx = 5.59in3. Factored Moment capacity of = 0.9*36*12 = 15.1 kip-ft.
Mr = 3*63/12 = 15.8 kip ft.


Factored or allowable load?

 

[TDIengineer]

And I would be worried about the base moment, if you use a 3/16" fillet, the effective throat is .707 of .1875 unless you can do a complete penetration weld.

You can't fully develop the 3/16" material with a maximum 3/16" fillet.