30 ft Bent Lamination

[Brett Bauman]

Hello everyone, this is my first post on here. I am looking to build a 30 foot bridge over a pond and was wondering the best way to do it. I would like to use arched beams, but was not sure the best approach. I was thinking of doing it two different ways; the first way would be to bend the boards in 4 sections and then attach them with possibly a bridle joint with bolts. My other thought was to make one big form spanning the entire length and staggering the seams on the glue up. Are either of these methods possible or am I way off? Also, it's just a pedestrian bridge with light traffic and the arch would be low.

[Jim Matthews]

It will work, if the footers are stable on either end of the span. If the arch isn't constrained, it will try to "splay" under load.

[Brett Bauman]

Ok, I already have the footers in actually.

[Tom Bain]

A 30’ lamination seems simultaneously daunting and awesome, but please do it and post pictures!

[Matt Day]

My gut says to use bolted and glued bridle joints, making the sections at your shop and assembling on site. But I don’t have any experience with this or anything. Sounds fun!

[Lee Schierer]

You don't say where you are located, but there are companies that make exactly what you are looking for. If you figure the cost of a 30 foot form and the labor to glue up two beams you might be ahead to have them made for you. Curved Glulam

[Bradley Gray]

Whether built in sections or made as one lamination at some point you will have to set the arches in place. I can't picture a way to assemble sections over the water. It will take some experimenting to determine how thick the lams can be and cold bend. I would use plastic resin glue and tack layers with a nail gun then use every clamp I have.

Maybe you could borrow a pontoon boat or two.

I wanna see pictures too!

[Steve Rozmiarek]

Fun! I've done much smaller bent lam, it worked surprisingly easily in my instance. Wax paper is your friend to keep the glue off everything else. It turned out much heavier than I expected to, yours will definitely require some equipment to place. Around here there are some old quonsets with bent lam framing, of about the size you are thinking, they are really strong buildings.

[Brett Bauman]

I do have access to some equipment to set these in place, thankfully. The bridge is actually over a dam. I am located in Ohio btw. I'm very excited for this project and will post pictures as I progress. I was thinking of using 1x6 pressure treated lumber, would plastic resin glue be the best?

[Phil Mueller]

Brett, I have no experience in what you are doing, but just wanted to say welcome to SMC and look forward to seeing pictures as well! Go Blue!

[Steve Rozmiarek]

I do have access to some equipment to set these in place, thankfully. The bridge is actually over a dam. I am located in Ohio btw. I'm very excited for this project and will post pictures as I progress. I was thinking of using 1x6 pressure treated lumber, would plastic resin glue be the best?

I don't know the answer to the glue exactly, but I do know that the glue companies are usually pretty helpful on picking. There will be a rep you can talk to. They don't want your project to fail from wrong glue either. If I had to guess, I'd say Recorsinol, but I may be wrong. Keep in mind that pressure treated wood is notoriously wet and moisture content may dictate glue choice.

[Bruce Wrenn]

My concern isn't the glue, but rotting of wood. In summer of 1967, I worked for Koopers Co in their laminating plant in Morrisville ,NC. Any wood exposed to the weather was treated to resist rot (Pelon treaded,) and glued using resin glue. Interior stuff was glued using Casin glue (made from milk.) You may want to add a truss rod to bottom of arch to prevent spreading. Where bolts from truss rod enter beam, you probably need to add TECO rings to reinforce the area. I surprised I can remember this as it's been 53 years now! Now where did I put my glasses that I just took off?

[Erik Loza]

You don't say where you are located, but there are companies that make exactly what you are looking for. If you figure the cost of a 30 foot form and the labor to glue up two beams you might be ahead to have them made for you. Curved Glulam

I would vote for this solution. ^^^^ Not that it doesn't sound like an awesome project but for the possible liability issues if it were to collapse under load. Also, the most stable outdoor woods (Ipe, teak, etc) would probably be a huge challenge to bend. Good luck in any case.

Erik

[Alex Zeller]

I think gluing will be a challenge. Pressure treated lumber would need to be dry before trying to glue it otherwise bonding and shrinking could be an issue. The exotic woods, like Ipe, don't glue all that well. The glue not only needs to hold the arch together it's also going to be subject to what ever load the bridge is carrying. The last thing you want is a failure. You could use something like white oak. I might even think about creosote on the ends to give them better rot resistance.

[Andy D Jones]

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