2x6 joist span for simple foot bridge

[ArlyA]

If you care, your railing posts will wobble quite a bit attached to the 2x8 stringers. Even with the 4x12's we used in our last structure, the posts wobbled much more that I thought they would.

 

[LD1]

Need blocking between the joists where the handrail posts are. The wobble is typically only because the joists is twisting. Blocking or x- bracing like you commonly find in basement ceilings for the floor above, resists the torsional force on the joist

 

[RobA]

So far I have several 2x4 braces screwed width wise to the bottom of the 2x8's to stiffen them. The 4x4 railing posts are fairly stable without much wobbling. I plan to add 1 more 2x4 in the middle of the span that extends about 2 feet wider than the bridge. From that I will add braces to the middle 4x4 posts.

 

[ArlyA]

What you call "blocking" are called diaphragms by the engineer dept. We of course added them because the stringers loose strength as they begin to collapse or twist and eventually fail due to that. For the bridge I posted photos of above, the railing is not connected at its center, because the bolts holes at a beams center will create stress raisers right where the beams stress is greatest. Even with the "blocking" these overly large beams twist and allow the railing to wobble more than I appreciate. Nonetheless we jumped up and down on it and this structure felt rock solid.

Need blocking between the joists where the handrail posts are. The wobble is typically only because the joists is twisting. Blocking or x- bracing like you commonly find in basement ceilings for the floor above, resists the torsional force on the joist

 

[Larry Caldwell]

I would flip the truss on the railings if I was to do something like this. But I wouldn't want to rely on an exposed wood truss for support. Too much shrinkage and movement of the wood o er time for me to trust it.

My dad built a steel truss foot bridge in the '60s that is still in excellent shape. Materials were 1"x2"x0.125" tubing and 2"x2"x.185 angle iron for the deck supports. The deck is 2x6 pt, but they don't let you buy penta any more, so new stuff probably would need replacing every 20 years.