Square Tube VS Formed and welded profile?

[BRHMFG]

I'm building a structure from steel to support multiple columns as an alternative for concrete. Currently I am using a profile of (3) 5" square tubes spaced 5" inches apart. In this case I have 12 columns in a circle, so imagine a 12 sided polygon. Columns are on the joints and there is a heavy plate on top and a vertical plate that the tubes are welded to on each side. I'm considering eliminating all the tubing and rather using plate to form my own profile with CNC plasma and press brake. I'm not sure it will be more cost effective.
With the tubing, its hard on our saw to cut accurately mitred corners to eliminate gaps when welding 3 separate tubes on each side of a joint. With CNC cutting I would at least have accurate mitres and lengths.
My question is: what shape of profile could I make that would be as strong or stronger than 3 square tubes? Has to be quite basic as my tooling is limited and it's only an old mechanical press brake. The length would only be from 5' to 6' span each section.
Essentially I could make a giant rectangle tube but I imagine I would need a few more vertical uprights than only the edges. And If I would have the top and bottom a solid plate how many less verticals could I get by with? That would create one closed profile versus 3 separate profiles. I'm not versed in stress analysis or that type of thing so if anyone can point me in the right direction I'd appreciate it.
Here is a screenshot:

 

[gbent]

Anytime you need strength, depth of section is your friend.

You have given us about zero to go on as far as loads. We need to know both the supporting loads from the bottom and the loads that are being supported from the top.

GIGO

 

[BT Fabrication]

concrete is mass......... much different then just ground pressure. mass keeps things from moving.

 

[Scottl]

One possible issue I see is that no matter how accurately the flat stock is cut any discrepancy in bending could still cause gaps at the miters.

Are you using a cold saw to cut the tubing or a horizontal bandsaw?

 

[memphisjed]

Tube is a lot cheaper and easier. Hard to grasp what you are really after. Rolling tubes would eliminate a lot of the welding. Gaps are not deal breakers in structural. Most large section call out 1/16 to 3/16 gap for easier back gouging.
“If you can step across it you can weld across it.”

 

[cyanidekid]

wow, well not sure ive got any freakin idea what the hell you are trying to do from the rambling, vague post, but unless you have free labor and machine time, its virtually impossible to bend up a section that is cost competitive with factory made tubing.

that shit is made literally by the mile per week, how exactly, unless ^ the above, are you going to compete with that economy of scale? oh, and WHY? what exactly is the advantage that you think your going to get?

id suggest from your post you get some advise regarding any structure that could fall on anything even remotely important.

 

[Luke Rickert]

Putting on my engineer hat, you need professional help! This isn't that complicated but you need some basic knowledge and given the costs of building something this size a few hours of engineering isn't really a big deal.

Luke

 

[BRHMFG]

Hey thanks for the input, ya I'm guessing tubing is the simplest way to go. Just thot I'd ask seeing that tubing is usually the highest price per pound. We use vertical bandsaw.

 

[Scruffy887]

I would form my own tube shapes only for a few reasons. 1st is that the formed shape has many holes, tabs, funky extra flanges. Because I have a fiber laser to cut them.
2nd is because I have a CNC press brake to precisely form needed parts.
3rd reason, laser flash, form, maybe TIG flash or spot weld, then done.

 

[metalmagpie]

Not to say the emperor has no clothes, but has a real welder looked at those plans and said it's all weldable? Looks like a ton of super tight out of position welding.

That said, if you want to make a nice bend in square tube, use a torch or whatever you like to cut out a triangle that reaches nearly to the other side. Then heat the bend line until red and pull the free end to the desired angle and tack it. Keep doing that, butt welding on new square tube as needed, until you have gone all the way around. On the outside there will be no visible weld on the corners. Best to make your cuts kind of sloppy and leave gaps to weld up.

Don't forget to add weep holes so rainwater can escape.

This reminds me of building the bow of a ship.

metalmagpie

 

[Cole2534]

Anytime you need strength, depth of section is your friend.

Structural design is a lot like real estate- it's all LOCATION, LOCATION, LOCATION. Depth of section is the best place to get it.