Which shape is stronger?

I have a few sheetmetal corners i need to add some strength to. 90ish degrees, panel about 3-4 feet long. Access to backside. 

Which would be stronger: 16 gauge 1/2 round tubing,  or 16 gauge 1/2 square? These are arbitrary numbers , but pretty close to what i have here to use. I would be stitch welding to the non visible inside corner across both planes for the length of the panel.

Square would be a little stiffer/stronger, round would be a little lighter.  Also, square puts the stitch welds to the panel farther from the folded corner which would help stiffness a little, too.  The welding would be easier with square, too.  I'd go square.

But the square would have a stress concentrator at each corner. 

A sharp 90* bend vs a 90 with a bit of a radius in the corner, radius is stronger.  So.....   one continuous radii is the strongest?

In reply to 914Driver :

If its a perfect square, yes.  Assuming he isn't working with aluminum tubing, all steel tubing I've seen has rounded corners.

It depends on where the forces are coming from.  
   Modern Trans Am cars have pretty much switched to small diameter thin wall   square tubing.  
     It actually makes a stiffer lighter chassis. 
  Back in 1954 Jaguar introduced the thin wall square tubing for their D type Jaguar.   
       With about 250 hp. They were able to go 183 mph with an engine that weighed 730 pounds bare. Their whole chassis only weighed  39 pounds. Made out of aluminum.  The next year they switched to steel and lost 17 pounds  for a total of 22 pounds.  That chassis was brazed together, not welded.  And the same basic chassis was used clear until 1974. Yes it passed the US safety crash tests!!!  
  My first wife crash tested it showing off to her mother at somewhere around 140 mph she lost control and totaled the whole car.  Her mother emerged with no damage( but scared) and my wife had a couple of minor bruises.  There are plenty of pictures of that bare chassis if you simply Google Jaguar XKEBare Chassis. 

The Pyramid.  The strongest shape ever constructed.  A shape that fits all other shapes inside of it.
 

So I guess a little more explanation is in order. This will be used to reinforce folded corners of 22 to 24 gauge sheet metal such as fenders and dashes on my race car. This is in the hope that when my fat ass doesn't think about it and leans on the fender or Dash to do something I don't bend the ever living berkeley out of it. Also would be nice for it to resist crumbling inward with a knee or a tire rolling into it. Sounds like Square tube is going to be my best bet for this.

A straight side would be best done with a sheet metal break, just bend a 90 on the edge.  Welding a tube onto sheet metal is going to give you some surface finishing issues, and creates an area for moisture and dirt to get trapped between two layers of steel.  Plus, weight.

Added bonus, you get to buy a new tool.

In reply to Streetwiseguy :

Or you can use some wood clamped together as a hack brake. 

Dusterbd13-michael said:

So I guess a little more explanation is in order. This will be used to reinforce folded corners of 22 to 24 gauge sheet metal such as fenders and dashes on my race car. This is in the hope that when my fat ass doesn't think about it and leans on the fender or Dash to do something I don't bend the ever living berkeley out of it. Also would be nice for it to resist crumbling inward with a knee or a tire rolling into it. Sounds like Square tube is going to be my best bet for this.

The square tube frames I mentioned earlier were made from even thinner steel. Probably 24-26 guage stuff yet it held a 730 pound engine.  
            Really if you want a really strong corner to lean on simply bend it 90 degrees.   Some of the "styling features on modern cars are there simply to add strength. 

I actually do have a break already. I'm trying to reinforce the 90 to make it even stronger. This may be a case of me overthinking the hell out of it though

In reply to Dusterbd13-michael :

Tack in some sheet bent Ls on the back. That would stiffen it up wo beading the sheet with a roller. 

In reply to Dusterbd13-michael :

Look at cars.  Most are unibody which is just sheet metal slightly reinforced in selected areas.