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! :D

[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 (https://www.americanlaminators.com/proj/curved.html)

[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! :D

[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 (https://www.americanlaminators.com/proj/curved.html)

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

[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/lostempires/china/builds.html

[Roger Feeley]

Another link with a better description.
http://support.sbcindustry.com/Archive/2004/jun/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]

438973
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.

[David Gutierrez]

If the abutments and arch are adequate a simple arch would carry pedestrian traffic full span for ages.
how do you reach that conclusion with no design load, bridge width, beam depth or arch height info? 30' feet is a decent span and should really be looked at by a engineer. typically bridges have higher safety factors and design loads then buildings.

[andy bessette]

https://sawmillcreek.org/images/misc/quote_icon.png Originally Posted by Mark Bolton https://sawmillcreek.org/images/buttons/viewpost-right.png (https://sawmillcreek.org/showthread.php?p=3045658#post3045658)
If the abutments and arch are adequate a simple arch would carry pedestrian traffic full span for ages.


how do you reach that conclusion with no design load, bridge width, beam depth or arch height info? 30' feet is a decent span and should really be looked at by a engineer. typically bridges have higher safety factors and design loads then buildings.

It is like saying: "If we had ham, we could have ham and eggs, if we had eggs." :)

[Steve Rozmiarek]

Andy and David, seriously, engineers are useful but they are by no means the only ones capable of determining the soundness of a structure. Lots of skilled tradesmen are just as capable or even more so because of a vast amount of real world experience. The reason engineers are used in construction is liability indemnification, it has usually has little to do with a tradesman's ability to design a solution on his own.

[jim sauterer]

I am in northeast Ohio.where is this in Ohio would be interesting to see.best wishes on your project.

[andy bessette]

... The reason engineers are used in construction is liability indemnification...

Actually the reason engineers are used is because it is they who are best qualified to design a safe structure without an inordinate waste of materials.

[Matt Day]

....waste of materials.

They make up for the wasting of materials by charging the client up the wazoo. Maybe I should have my next coffee table designed by an engineer to, in case someone decides to drive a car over it.

[Steve Rozmiarek]

Actually the reason engineers are used is because it is they who are best qualified to design a safe structure without an inordinate waste of materials.

Umhmmm. At no regard to the extra cost of labor or real world cost of materials in my experience. Example, needed a load bearing beam engineered into a recent build. I wanted to use a simple steel 12" I beam that was already on site. The engineer wanted to custom order a smaller beam because the one I had was more than necessary. Custom order, $$, shipping time $$, stopping progress, $$. I threw a bit of a fit, and he signed off on my beam. What's the sense in that?? I'm sure there are some fantastic engineers with experience enough to not get in the way, but this guy was not.

Another example, one of our shop builds had 18' sidewalls. Actually the one on my avatar. Code says that even though its on a foundation, because it is framed like a pole barn, the "poles" had to be engineer stamped. They are a horrible product, the ones we site build are far superior for straightness and structure. It's just three 2x6 stacked together with glue. Stupid to pay more for an inferior product because an engineer is getting a cut.

[johnny means]

Just gonna leave this here.
https://youtu.be/PYkgEf3eWqA

[John Ziebron]

Years ago I built a bridge on a smaller scale for a step-daughter and son in law. I used all clear cedar except for the planks which were a lower(cheaper) grade with some knots. I think cedar would be a good choice for the rot resistance and lighter weight, especially for a 30 foot span. My 2 beams were simple cold bent laminations using 3/4 thick stock glued and screwed. I had to transport this to Ohio so I designed it to be completely taken apart using all stainless steel hardware. This bridge was almost 10 feet long, but as someone suggested, staggered joint lamination would work well, especially since yours would be also only be a pedestrian bridge.

[Steve Rozmiarek]

Just gonna leave this here.
https://youtu.be/PYkgEf3eWqA


That's pretty cool, I like the small scale rails.

[Mark Gibney]

Great video! Man, he just makes it look so natural and easy.

[David Gutierrez]

just by the nature of the question it is apparent that the original poster needs help understanding what is required. A 30' span, while tiny for a bridge, is beyond many peoples experience. this is not something you can take out of building code span tables. He needs some ones help to design the bridge, logically that is a engineer. my point was that one cannot know if it will work with out knowing the parameters of the bridge. the 10" bridge above can be done by someone with experience in carpentry, a 30' bridge is a different animal.

[William Hodge]

I started out my woodworking career in a laminated beam shop. We were doing interior work, but we made the beams out of southern yellow pine, untreated. We would rip 2 x4 stock into 1/4" x 3 1/2" strips on a gang rip saw, apply barrels of glue, and wrap them around a steel frame. The "wrapping" involved 1' threaded rod, steel plates, and a pneumatic wrench. It was loud.

I learned several tings there, one of which is don't stick your hand in a running planer. But that's not what I came here to write about.

All the beam designs, and their applications, were passed by an engineer. This was to make a better product that would be safe on site. I learned that when you make stuff, you bear a special responsibility to the people of the future to make sure you aren't doing something that will injure them.

What is the purpose of the 30' bridge over a dam? Is it open to the public, or just for family and livestock use?

Or, is it going to be there for a drunken wedding party in high heels?
439364
Elm Park Bridge, Worcester, MA
The bridge is steep, many brides have gone for rides.

In New Hampshire there are covered bridges with arch supports. The arches I have seen are protected from the weather. I don't know what they are made out of, but there was no waterproof glue back then.

439365

Coverered Bridge in New Hampshire

[Andy D Jones]

While I'm certain knowledgeable tradesmen have had poor experiences with engineers, the opposite is undoubtedly common as well. And I bet stories arising from the latter (or failing to consult with an engineer) are much more entertaining, if not horrific.

First off, engineers (should) work from the requirements given them. Poor requirements in, poor results out. Sometimes, an engineer will make inappropriate assumptions, not based in fact, especially if not given the facts in the first place. If the request given the engineer is "design a beam that will work for this" vs "design the support for this existing beam, to span this", the answers will likely be very different.

That said, there are poor practitioners in every discipline, including engineering. I don't think we would judge the skill of woodworkers in general based on the least capable woodworker. We should not judge engineers likewise either.

Disclosure: I am a retired electrical engineer, specialized in electronic design. I am NOT a Licensed Professional Engineer. I am also not nearly as talented a woodworker as I am an engineer.

-- Andy - Arlington TX

[Mel Fulks]

I would ask whoever it was that wanted to build that "bridge to the twenty first century" WE GOT HERE!
Only problem with some engineers is they delight in clever material saving at high cost. Like the defunct twin towers.
I would look at pics and sizes of old bridges and copy.

[Steve Rozmiarek]

While I'm certain knowledgeable tradesmen have had poor experiences with engineers, the opposite is undoubtedly common as well. And I bet stories arising from the latter (or failing to consult with an engineer) are much more entertaining, if not horrific.

First off, engineers (should) work from the requirements given them. Poor requirements in, poor results out. Sometimes, an engineer will make inappropriate assumptions, not based in fact, especially if not given the facts in the first place. If the request given the engineer is "design a beam that will work for this" vs "design the support for this existing beam, to span this", the answers will likely be very different.

That said, there are poor practitioners in every discipline, including engineering. I don't think we would judge the skill of woodworkers in general based on the least capable woodworker. We should not judge engineers likewise either.

Disclosure: I am a retired electrical engineer, specialized in electronic design. I am NOT a Licensed Professional Engineer. I am also not nearly as talented a woodworker as I am an engineer.

-- Andy - Arlington TX

I think you are talking to me, so I'll offer my $.02. I hate red tape. If I'm spending time dealing with unnecessary bureaucratic steps in building, then I am not making money. In fact when I'm dealing with red tape, someone else is taking money from me for often bogus reasons. The local building code is full of unnecessary stuff that does just that. For example, a shop building over 3000 sqft here requires an architect stamp. However, if I were to build a 88x36 building (3168 sqft), and add a firewall in it that divides the space in increments less than 3000 sqft, I can skip the architect stamp and save a pretty considerable amount of money. It's the exact same building, just that the more complicated one is cheaper. Some industry lobbyist got that into the code I'm sure, and that is the problem. It dilutes the value of the engineering trade to builders because we get to the point where it's a minefield of irrational regulations and the best strategy to get through it unscathed is just to avoid anything that mandates engineers or architects as much as possible.

That being said, I do definitely agree that engineers are useful and valuable in lots of things. I actually intended go into the field many moons ago, and if I was smarter I would have finished that career path.

[Jim Barstow]

I did a 13' bent lamination and although I love the result I don't think I'd ever want to do it again.

I really think you need to have an engineer's input. For those who have complained about engineers, they probably didn't specify what they wanted up front; if you just throw plans at an engineer, they'll treat it as carte blanche. ("I have an existing beam. Can I use that?" vs "What kind of beam should I use", for example.) I built a deck for a yurt that required the beams to be carried over 100 yds down a trail by just my wife and myself. I specified that fact to the engineer and he figured out how to do it with smaller dimensioned, lighter materials.

With a 30 foot bridge 5 people standing in the center there's a pretty big load 15' away. I'd be thinking, "What if I guessed wrong and it drops people, and maybe kids, into a pond."

439410

[Andy D Jones]

I think you are talking to me, so I'll offer my $.02. I hate red tape. If I'm spending time dealing with unnecessary bureaucratic steps in building, then I am not making money. In fact when I'm dealing with red tape, someone else is taking money from me for often bogus reasons. The local building code is full of unnecessary stuff that does just that. For example, a shop building over 3000 sqft here requires an architect stamp. However, if I were to build a 88x36 building (3168 sqft), and add a firewall in it that divides the space in increments less than 3000 sqft, I can skip the architect stamp and save a pretty considerable amount of money. It's the exact same building, just that the more complicated one is cheaper. Some industry lobbyist got that into the code I'm sure, and that is the problem. It dilutes the value of the engineering trade to builders because we get to the point where it's a minefield of irrational regulations and the best strategy to get through it unscathed is just to avoid anything that mandates engineers or architects as much as possible.

That being said, I do definitely agree that engineers are useful and valuable in lots of things. I actually intended go into the field many moons ago, and if I was smarter I would have finished that career path.

That building size limit is not the issue. You'd only need to create a 13x13' storage room in a corner (fewest feet of firewall) to escape the requirement. Or you could just build a 83x36' building in the first place.

No matter what the limit is, there will always be cases that are just under it, and realistically just as risky, but not needing an architect, or just over it, and not significantly more risky, but needing an architect. No matter where you put the limit, there will always be cases, near the limit, on either side, that don't make perfect sense.

The customer needs to decide whether they really need that extra 168.1 square feet.

There's always politics, in EVERYTHING. And that, most assuredly, is not the fault of the engineers (or architects)!

More importantly, in any market, for any product, there are always steps in the cost curve, artificial or not. The smart customers (and smart builders like you) know where the steps are, and can advise or act accordingly.

In electronic design engineering, it was our job to know where (and how big) the steps were, and design accordingly, for each "cost" curve (not just $, but also weight, size, maintenance, production volume, etc.)

-- Andy - Arlington TX