Say you're going to make a bridge. You can choose between a square tube or a rectangle tube for the frame. Using just arbitrary numbers for easy figuring, use a 12"x12" square, and a 8"x12" rectangle on edge. Same wall thickness.

 Both tubes have the same vertical measure, but the rectangle would have the vertical sides closer together than the square.

 Which would carry more net weight in the center of the bridge?

 Using the I beam designs, I feel the rectangle would carry more net. Am I right or wrong? What do I need to type into google to find more answers?