I need to create a 15 feet span beam for kid swing (300 lbs load / 150 lbs and 2 swings assumption). One end will bolt to the tree (just for convenience).
What "treated lumber" lumber size and material I should use? Or is it better / cheaper to use metal pipe (from the plumbing department)?
I guess 4x8x16 or two (2) 2x8x16 would do it according to this website http://www.justanswer.com/structural-engineering/7vgxr-building-swing-set-16-ft-span-bolt-2x6.html. But I do like a clean look of metal. My wife would concern about big piece of lumber running on top of the kid (that looks heavy visually).