30 ft Bent Lamination

[Bob Jones 5443]

Why bend at all? If you have access to an 8" jointer and a bandsaw, you could give the entire span the same radius (probably at least 60'). You could mill several 2x8s flat and square, and then trace and saw the arc on every board. These could be triple laminated and staggered, creating a mechanical bridal joint at each juncture. You'd need to crosscut off the ends radially to the circle to make clean butt matings.

If it's not too sacrilegious to your design concept, the use of bolts would produce strong joints and the only glue you'd need to be concerned with would be in the laminations. While I'm at it, you could bolt the entire span if that wouldn't clash with your vision for the structure. To me this seems easier and more consistent than bending thinner stock. Also, no forms required, just a long trammel string or wire to draw the 60' radius.

If, like me, you're stuck with a 6" jointer, you can still do the job with 2x6 boards and use a longer radius. Note that a longer radius would produce less waste in the stock, but there is a limit: the "straighter" your bridge, the more bending stress you put on it, whereas a higher arch (smaller radius) would provide more vertical load support. Somewhere in the middle will be the sweet spot aesthetically, too.

Like others here, I eagerly await your documentary photos! Good luck.

[Roger Feeley]

If you feel gutsy, skip the laminations and go for some ancient Chinese tech.
https://www.pbs.org/wgbh/nova/lostem...na/builds.html

[Roger Feeley]

Another link with a better description.
http://support.sbcindustry.com/Archi.../Paper_016.pdf

[Brett Bauman]

I was also considering using white oak and I think that I will use that instead. I live on a farm where my county does not require permits if it is on a farm.

[Frank Drackman]

I have nothing to add except to say what a fantastic first post! Sounds like a great project, & look forward to reading more about it.

[Mark Bolton]

What is the vertical rise in the arch? If its not much I would just build your large forms and lay up with either 2x or 1x material to form your beams with epoxy and simple staggered joints. Most of the treated material out there now is like a wet noodle when you buy it. Springing 16' 2x's over a form with a modest arch would be pretty simple. No joinery needed at all just a lot of clamps.

[Roger Feeley]

My cousin (a 1%’r) built a house in Hilton Head and spared no expense. He told me about having 30 foot curved beams built. Some months later, I read a short article in FWW by some contractor about having to make 30ft curved beams for this uncompromising (jerk) client in Hilton Head. His solution was to suspend his 16” bandsaw on an air cushion and push the bandsaw through the beam instead of pushing the beam through the bandsaw.

So all you have to do is turn your bandsaw into a hovercraft, put on a re-save blade and go for it. No bending.

[Bradley Gray]

Brett, where in Ohio are you? Sounds like my part of the state. I'm in Adams County.

I live on a farm where my county does not require permits if it is on a farm.

[Mark Bolton]

I live on a farm where my county does not require permits if it is on a farm.

Also keep in mind that permitting and following building code typically means the MINIMUM ALLOWABLE STANDARDS. All too often people thing "the code" is over the top overkill. In actuality the minimum code is pretty much the bare minimum to keep your structure standing for a period of time. Most anyone or any locality will exceed that code based on local conditions.

My guess is without a doubt anything you build without an engineer will likely be 9 miles of overkill that could support a sherman tank.

[Mel Fulks]

Agree with Mark on that code thing! My image of routine code overkill is the Boy Scout who digs the latrines ....an inch
deeper than the "manual specs" !

[Steve Rozmiarek]

Also keep in mind that permitting and following building code typically means the MINIMUM ALLOWABLE STANDARDS. All too often people thing "the code" is over the top overkill. In actuality the minimum code is pretty much the bare minimum to keep your structure standing for a period of time. Most anyone or any locality will exceed that code based on local conditions.

My guess is without a doubt anything you build without an engineer will likely be 9 miles of overkill that could support a sherman tank.

Farm guys could certainly build a tank bridge! Ditto on the codes being minimum. In fact yesterday a building inspector asked me why the foundation we were discussing was an extra foot deeper than the code, while standing beside a cracked code compliant old foundation. Code plus common sense usually equals pretty good results.

[Curt Harms]

The fact that you are asking help here tells me at least you understand that this is at the edge of, if not beyond, your current capability.

Seek at least design support from a professional firm.

When people are to be suspended over water, on an inadequate structure (or even an inadequately maintained one) there is a significant chance of serious injury or death, almost regardless of how high the structure is. This is a liability issue for which you need professional engineering, if not also professional fabrication.

Are you in an area where local building codes and inspections are required?

-- Andy - Arlington TX

I think this is good advice. If you were fabricating a short footbridge over a usually dry swale it'd be one thing. A 30 foot span over water isn't DIY territory to me.

[David Sochar]

Pergola Arch.jpg
We made a 36' long laminated box bean, non- structural for a poolside project. 12" wide Cedar, 1/4" thick, joined with scarf joints for length, bent on a form of sorts, and then placed into the upper and lower 'faces' of the beam. Epoxy, Western Red Cedar, KD, and scuffed faces on the laminations.

I have recently learned that about 20% of W R Cedar has so much oil/resin that TB 1/2/3 and other water based glues are failing to set. The practice of wiping with acetone may help, but is hit or miss. How will you do that with mortise and tenon joints?

I also learned that a freshly cut surface glues better than one that is a day old. I'd scuff each ply just before gluing. Epoxy is a rare glue in that it is a true gap filling glue with strength even in the gaps, and it does not like/require lots of clamping pressure.

If I were where you are, I'd build the form for the one piece beam. Plan on 3/4" W Oak. Scarf them together, staggering the joints. Buy lots of epoxy.

[andy bessette]

A 30' span would suit itself to a truss. It should be engineered by someone with experience at designing this sort of thing. A curbed beam does not lend itself to this application.

[Mark Bolton]

A 30' span would suit itself to a truss. It should be engineered by someone with experience at designing this sort of thing. A curbed beam does not lend itself to this application.

If the abutments and arch are adequate a simple arch would carry pedestrian traffic full span for ages.