Building an arched bridge

[mysticokra]

I would like to build an arched bridge over our stream. I need to span about 20 feet and think a rise of about 2-3 feet would be sufficient. Has anyone seen plans on how to do this?

This bridge will be for foot traffic.. and maybe a riding mower. I plan to build it out of wood. It's an aesthetic delight as much as a functional device.

It's the curve in the support structure that I could use some direction on. I suppose I could build laminated beams that attach to sunken posts. That's why a set of plans would be helpful.

[GaryM]

The one in your photo looks to be about 12-15'. It's a lille shorter than what you wanted. Looks like the side are one piece. I'll bet you could make the side out of plywood sections laminated with the joints staggered. I'd use a good water proof glue. Maybe a marine epoxy such as West Systems. Two or three layers of 3/4" ply might be strong enough for each side piece.

Is it only to have supports at the ends, or can you support maybe at the 1/3 point? That would take a lot of stress off the sides.

[egon]

For "FOOT TRAFFIC"you could laminate or use solid stock with plate's on the joints.

For looks the laminated may give a nicer look as it could be made with a continuous arch. Consider fabricateing a one piece gluelam type beam from solid stock. Say 1x3 inch material that does not have to be full lenght but has stagered joints. Suggest about 10/12 inches deep using resorcinol or best; epoxy glue. Thouroughly paint the finished beam with a wood presrvative.

To make the beam build a frame to which the first few layers could be clamped and the arch set. Then screws and clamping for the remainder.

The beams may be easier to fabricate than you think. The base frame is the important part. Construct it on the flat at a convienient location. For a natural curve fix the end points and set the mid height desired. use some very thin material to bend over this to define the curve and then set up some braces that the can be used as clamp points. Make it at least a foot longer on each end so it can be trimmed.

Most of the bridge could be built offsite and then moved into position. Consider concrete for the end support piers

Please note: I have never done this so the advice and technology may/is questionable.

Egon

[fivestring]

<font color="green">"Please note: I have never done this so the advice and technology may/is questionable.
Egon " </font color>

But you did stay at a Holiday Inn Express one time, didn't you?
[img]/forums/images/icons/smirk.gif[/img]

[egon]

Gary:
If I was paying it was the backseat or a hostel. If the company was paying it was first class.

Egon

[kcbarnes]

Sorry it took so long to reply but here is a bridge I built about 10 years ago.It is 17' long and 40" wide built from tulip popular cut from our property. I built a jig from 2 sheets of osb set end to end and attached an arch support to it and then started bending and glue/screwing the 3/4x4" boards to it staggering the joints and screwing the first layer from below and all others from above untill I reached about 12"tall. they will hold me and a push mower with no problem but the deck boards have not held up so they need replaced.

[dummy]

Rather than using smaller stock and bending, why not use larger 2x material and cut the arch out of the laminated beam?