How long can I span with a white oak 6x12 (for a foot bridge)

[burdman_22]

Im wanting to build a pretty simple foot bridge with a couple of loooooong beams. I need to span about 50 feet. Can white oak 6x12s span this and still support the weight?

I assume even if there is SOME sag it's ok, since it is just a foot bridge...I think we'll just be covering it in planks and putting a railing. Can make the beams for the span a little larger if needed.

Thanks for any tips/advice.

[doc henderson]

I do not know the math, but maybe the railing can be trussed and offer some rigidity, so it is not bouncing up and down with every step.

[chep]

Why mill them into beams? Just skim flatten the tops and put decking on leaving them almost complete. That will retain the most strength.  Whether or not it is strong enough to span 50 ft I don't know, but certainly stronger then the stated beam

[Rhodemont]

I like Chep's idea.

You can mill 50 feet?  If so 6 x 12 is small.  How high above ground/water will you be?  A couple PT posts drive in along side and screwed to your  beams will add a lot.

[Stephen1]

I think Doc has the best idea and that you use your railings to create a truss system that  will help support the beam

[doc henderson]

Is it over water?  You can span that but if there is dirt along the way, some pilons will also stiffen the beams.  At camp we made one 36 feet and put pilons set in concrete in the middle as is only saw much water after a rain, but the ground was muddy.  6 feet wide and can drive 4 wheelers across it.