I built a footbridge to cross the ditch next to the house probably 25 years ago. It's showing it's age and Mrs. PHPaul wants me to build a new one.

I'm going to build a variation on this one:



Main differences are that it will be longer (16 feet) and I'll use pressure treated lumber.

To get the arch in the base, I'm going to layer at 2x4 on top of the 2x6 stringer and cut an arc in it from 0 at the ends to the full 3-1/2 inches at the center. Scratching my head trying to figure out how to lay out the arc as it's too big the use the ol' "nail, string and pencil" technique.

A little surfing got me to blocklayer.com and they have a calculator where you can plug in the length and height at the center and they will print out the height at any spacing you desire - ie, 0 at the end, 13/16ths at 1 foot, 1-17/32nds at 2 feet, etc.

I'll do a little rounding on the 32nds and it's gonna get cut freehand using multiple straight lines so it won't be perfect but it'll be plenty close enough for a footbridge.

Pretty cool project, be sure to post pics.

As far as your arced lumber problem, I'm pretty sure the Lowe's closest to me has all the bowed boards you would need in stock to knock that out

quote:

Scratching my head trying to figure out how to lay out the arc

Just head on down to the local Menards or Lowe's...mine always seem to have an excellent selection of curved lumber...the trick will just be finding the gradient you're looking for. Me, I'm usually looking for "straight", and I typically end up having to dig halfway down into the stack before I find any of those .

ETA: MattW beat me to it, lol

Hah! I should've thought of that. Deep Homo has plenty of pre-bent lumber too.

Do you think a 2x6 is strong enough for 16 feet? That 2x4 on top will not add any strength.I would go with a least a 2x10 and maybe a 2x12.

quote:

Originally posted by 9mmnut:
Do you think a 2x6 is strong enough for 16 feet? That 2x4 on top will not add any strength.I would go with a least a 2x10 and maybe a 2x12.

Normally, for a load-supporting header, I'd agree - rule of thumb is 1 inch of depth per foot of span.

It's a foot bridge that'll be 4 feet wide with 3 stringers. If it feels bouncy, I'll "T" another 2x4 on the bottom to make an L-girder.

Edit to add another thought - I think the uprights and double side rails will also act as a sort of suspension bridge type of bracing. Pretty sure it'll be fine.

Just a thought, but you could put a nail in each bottom corner, and one in the middle at 3-1/2 inches use them to form long piece of small diameter pvc or pex to make the curve template.

quote:

Originally posted by KDR:
Just a thought, but you could put a nail in each bottom corner, and one in the middle at 3-1/2 inches use them to form long piece of small diameter pvc or pex to make the curve template.

That'd likely work. Not sure I could find a piece of PVC 16 feet long and suspect a 16' piece of PEX wouldn't give me a consistent curve. I'll keep that in mind for other projects.

Did a sample layout on one 2x4 using the technique described in the OP and it looks pretty good. Probably cut that and use it for a pattern for the other two.

redwood bridges

I think this is where I got a bridge. Easy to assemble, solid.

I was in Home Depot this afternoon, I'm building a potting bench and need a little more lumber.

Good gosh, it's crap. Lumber is more crooked, twisted, bent, cracked up and around in every direction and warped than the california politicians.

I dug through a whole stack of 1x4's and it's junk. Just junk.

I think I'll look for someone tearing down an old house. I want the old lumber. That's something very much worth recycling.

Any lumberyards where they let you select the wood?

Got a good start on the new bridge today. Got the stringers cut and assembled. The layout technique from blocklayer.com worked very well. My old Makita worm drive had no problem following the slight curve. The 2x4 is screwed to the 2x6 on both ends and fish-plated in the middle.



The sod was removed and the ground leveled for the "abutments" which are 2x2 concrete pads, 2" thick. Only about 12 feet of the 16 foot bridge will be unsupported.



The stringers are installed and blocked and a couple of the decking boards nailed on just to keep things square.

I'll work on the decking tomorrow. So dang hot I get a couple of hours in the morning and a couple more in the evening before I poop out. Bulled through the heat until noon-ish today, had to take a shower before I could take a nap...

Posts and railings installed. Bowing the 2x4's to match the arch of the deck was MUCH easier than I feared. Placed the center in the middle post dado, put a screw in to hold it, put one end in and screwed it and then just leaned on the other end until it popped into place. Occasionally, being a fatass has it's advantages...

Wouldn't have believed it if I hadn't seen it with my own eyes. I was envisioning all sorts of ropes and pulleys and jacks and shit to get them in place.

All that's left is to put the stiles on the railings. Roughly 100 of them. Pre-drilled and screwed to the 2x4's. Job for another day. I can pre-drill them in the relative comfort of my shop and then screw them on in the cooler part of the day tomorrow. Or whenever.

After the treated lumber has a chance to weather and dry out a bit, I'll stain it to keep things from drying out TOO much and cracking. Especially the post caps.

Wow Paul. That looks outstanding! When I see projects like this, there are times I wish my backyard was more than 800 sq/ft.

Great job! Looks awesome.

Finished product. Caught a nice breeze this afternoon and was able to finish up.

Looks like a fun project - Well done!

Hey that looks nice, well done!

Bravo! You very artfully concealed the drawbridge mechanism.