Arched Garden Bridge

I have a lava-lined ditch dividing my yard with a garden and compost bin on the far side of it. The old 4x6 plank was a bit sketchy for wobbly seniors to use so replacing it was rather important. For this project I used 2 4x12 x 10' as the main beams and covered those with 2x6 x 4' planks. Here is how it went. 

Always looking for a deal, I picked up the 2  4x12's from the reject pile at the local lumber yard. These 2 were in that pile because they were curved - which suited my plans just fine. Fitting within the rectangular confines of 12" x 10' of the beam face, I pieced together a 22' pole that I used to scribe the inner and outer arcs. These are concentric and yielded about a 4x6 curved beam. 

To cut the curves, I bought a very nasty Diablo carbide tipped sawzall blade and started cutting. Working slowly I was able to get OK curves that I smoothed out with planes. The concave edge required I make a radiused plane body but I just rounded the bottom of a conventional kanna dai that I had. Worked fine for this rough task.  

Surely I did not need to cut dovetails into the beams for cross members, but my irrational ways have been on display on this blog for a long time. I wanted my cheapo beams to be parallel and not roll under load. I laid out the dovetails before I cut the curves. I used my Skilsaw to cut one side of each dovetail groove at 15 degrees but it only tilts to one side and these were stop dovetail grooves so I had to hand cut the other side and chisel the waste out. Slow. 

The cross beams were all resawed and ripped from some hefty cutoffs I had around. They are overkill but I wanted to get those cutoffs out of my shed (to make room for more cutoffs). 

Test fit. Getting heavier...

Next up was to notch out recesses for the eventual handrail posts. There would be 3 on each side of the bridge. A bit sparse and not what you would see at Nikko. 

These vertical posts are also from an old cutoff. While the bottom is square, I did taper the upper portion of the sides of each post. 

For the handrail itself, I ripped some strips of western red cedar and laminated those together with Gorilla Glue, using the beam as the form to create the curve. It sprang back a little after unclamping but that is actually welcome since it effectively increases the radius of the handrail curve. Tenons on the tops of the posts were transferred onto the handrails, which were then mortised. More Gorilla glue fixed the handrails to the posts. 

At this point I caulked and painted the bridge because we live in a rain forest part of the year. After that I had to wait until a stout visitor was able to help me carry the bridge up to the concrete abutments I had poured earlier. Some #4 rebar pins secured the bridge to the abutments. 

To plank the bridge I cut a bunch of 2x6 x 4' pieces of construction grade DF and took a 3" propane torch to them to make them "age" quicker and to match an adjacent shed. A couple coats of Copper Brown preservative made them very dark and able to shed water, but a few months will pass and they will lighten back up. 

I also cobbled together some rock and cement ramps to ease the transition to the bridge. I have since tried to hide the exposed concrete and that blue drain pipe but this is how it looked right after installation. In a few years it will be all dark and mossy.