Operation Bridge Rescuse

[Mad Professor]

Was watching PBS and came upon this in a Nova episode.

Massive timber frame covered bridge destroyed by hurricane Irene, then rebuilt.  Three huge trusses.  Used an interesting "saw tooth joint" to make a beam the length of the span.

"Follow the race to rebuild the Old Blenheim Bridge in New York State, an icon of 19th century American engineering, destroyed by Hurricane Irene in 2011. Watch a team of elite craftsmen faithfully reproduce the massive, intricate wooden structure under grueling time pressure as flooding threatens their worksite."





 

https://www.pbs.org/video/operation-bridge-rescue-l8xnj0/

[Dave Shepard]

Looks interesting. I'll have to watch that later. 

[sawguy21]

It is really interesting watching those long loads being moved. 8)

[samandothers]

Thanks for sharing, just watched the show.  Really interesting to see the approach to the build and setting.  It was also interesting to see the Chinese bridges and their engineering.  

It tied right into a recent thread on Leonardo da Vinci's bridge design and that the Chinese built the design prior to his time.  The Chinese design to hold the bridge down and absorb shock was ingenious.

[Magicman]

This engineering feat was well worth the watch.  ;)

[maple flats]

Amazing for sure, I just watched it!!! 8) 8) 8)

[Greyman]

Awesome.  The exploded views at around 15:30 are nice, with the sawtooth joint.    $6.7 million!!!  Reminds me of our old family farm barn - we paid more to have it painted in the 70's than it cost to build in the 1900's.

[D L Bahler]

Thank you for the link. Interesting video, and I'm glad for the bit of world tour they have given us as well.

From an engineering standpoint, the Chinese arch is similar in concept to the Da Vinci bridge, but not exactly the same. The CHinese employ two arches woven together, whereas Da Vinci's design features a single arch locked into itself. 

I would also like to add that they spend some time talking about the impressive old bridges in China, but relatively little time on the older bridges to be found in Europe. They did briefly mention the Kappelbrücke in Luzern, but did not give it the attention this wonder deserves. It's is, for example, the oldest extant wooden truss in the world, and some consider it may be the oldest intact (original) wooden bridge in the world. The impressive medieval trusses of Switzerland's bridges and the massive laminated arches of its more modern beams are a sight worth studying. I only say this because we sometimes see our own European heritage discounted in attempts to highlight the works of the east. Both are equally deserving of our admiration. 

That said, the work shown here in reconstructing this bridge is amazing. I wish that I had the chance to take on such a project! 

[JJ]

The heavy lifting and moving of structures takes steady nerves.  Wonder what kind of insurance bonds those guys carry.  Moving an entire lighthouse was impressive.

        JJ

[Mad Professor]

I'm glad some enjoyed the link.

I was impressed both by the scope of the project and that they tried to recreate 1855 with tradition of the build.  Moving the structure was simply ingenious.

I had never heard of a "sawtooth" joint.  Anyone ever seen it in a building?  Seems awesome under tension. That bridge was 22? feet long.

Others who posted here now have me researching what the De Vinci design was and exactly what the Chinese came up with centuries earlier.  I was ignorant of both.  If you have links, please post them.

[Don P]

We were talking about it a week or two ago here;
http://forestryforum.com/board/index.php?topic=103290.0

I've seen the sawtooth joint under... nope I just looked at a pic, well, under some bridge.

I was thinking this one, the last Haupt truss, it doesn't have the sawtooth but another unique bridge design;

Edit, this link is a better description of that truss. I remember Jim helping to pull a Town Lattice truss bridge out of the drink. This is the next evolution on that truss.
https://northcarolinahistory.org/encyclopedia/bunker-hill-covered-bridge/

[Mad Professor]

Hi Don,

Those NCSU links don't seem to get me to the place you're thinking of?

Regardless thanks for the help

[Don P]

I think I fixed it above.

[D L Bahler]

The outer trusses on this bridge make me think of this: 


     

Seeing the wooden arch (Holzbogenbrücke) caught me by surprise. I wasn't familiar with its use in America. Of course the wooden bridges in Indiana where I live are built much differently. 

Also the sawtooth joint I found a pleasant surprise. This, too, I am familiar with from European bridges. 
For a variation of this family of joints, look at the timbers comprising the arch in picture two on this post. 

[D L Bahler]

I wanted to go back and double check my information before I said this next bit. 

The sawtooth joint shown here is a simpler execution of the sort of sawtooth I'm used to, and appears to be turned 90 degrees in relation to how I'm used to seeing this joint. I have seen this as a sort of primitive means of laminating timbers together, allowing a single large cohesive beam to span a great distance. This would be a method whereby the beam is constructed of at least 3 timber layers, joined to each other with the sawtooth joints along their entire length. Doing this requires that no single timber need be very long to construct a very long beam. The joint is usually keyed with a small wedge in each tooth to drive it tight, before the whole assembly is bolted together. Examples of this sort of joint go very far back, perhaps to the late 17th century on wooden bridges in Switzerland and southern Germany, certainly it was in widespread use by the middle of the 18th century. 
One of the more remarkable situations where I saw this joint was in a saw shed built in 1841. The front wall had a beam constructed using this sort of primitive lamination technique to allow to construction of a tremendous free span without the need for a large truss above it. 

I'd be curious to learn anything more that any of you know about the laminated timber arch. It would be interesting particularly to me to learn how the original arch was constructed in the 1850's

[Don P]

Research Burr arch truss bridges and words around that.
It is different in that the arch and truss work somewhat independently.

I was bumping around and found a good timber bridge design manual from LSU;
http://www.ltrc.lsu.edu/ltap/pdf/timber_bridges_design_construction_inspection_maintenance.pdf
There is a picture of a Burr arch being dismantled in chapter 1, it looks like severe rot in the end of the arch. Chapter 2 is a good description of some timber bridge types.

edit;
This manual calls the sawtooth a bolt-of-lightening joint, fig 108;
https://www.fhwa.dot.gov/publications/research/infrastructure/structures/04098/index.cfm

[D L Bahler]

Thanks for the info. 

I'd guess you're a bridge fan! 

I've been analyzing a few differences between these different approaches to arch supported spans. 

A bridge like the old Blenheim bridge and the Burr arch trusses you show are primarily trussed spans with a reinforcing arch. 
In contrast bridges like the Horbenbrücke are supported only by their massive arch assemblies. 

This is best illustrated in the bottom chord of the bridge. The American bridges, being long trusses, require long bottom chords that act as single continuous structural units, hence the use of the "lightning bolt" or "Sawtooth" or whichever name you wish to use (Schräger Hackenblatt?) 
The Swiss arch, in contrast, completely lacks a true bottom chord. Instead cross beams are hung from the arch, into which the deck-supporting beams are laid. There is no single structural unit, aside from the arch itself, spanning the length of the bridge. 

Older Swiss bridges were king post trusses that had a relatively small limit on how far a clear span they could manage. Thus bridges like the Kappellbrück in Luzern or the Neubrück just outside of Bern had to have piers constructed under them. This made them susceptible to flood, and as such not many survived into modern times. The Kappelbrück benefits from being on a lake which does not change height drastically in floods, or have rapidly flowing water. The Neubrück was built very high above the Aar river, and as such managed to escape the damaging floods that destroyed most of its counterparts. 

The Horbenbrücke was the first arched bridge to be built in Switzerland. This was done because they decided, when replacing the old truss bridge, that they wanted no piers in the middle -a clear span. This bridge was built in 1834. Just 4 years later a terrible flood ravaged the Emmental, destroying bridges and many houses along the banks of the River. Only the Horbernbrücke survived in all of the upper valley, because it stood so high above the river that the flood waters simply passed under it (it's about 16 feet over the normal river level). As such, it became the prototype for all bridges built from that point on, culminating in the 68.7 meter (225.4 feet) long bridge of Hasle-Rüegsau in 1839, Europe's longest wooden arch.

 

 

 

 

 

 
(Pictures are of the 225.4 foot bridge of Hasle-Rüegsau)

[D L Bahler]

The German term for the sawtooth beams stacked atop one another is "Verzahten Balken" or toothed beams. 
The splice joint of similar design is called a "Schräger Hackenblatt" which might be translated sloped stepped splice. (Litterally word for word, crooked chopped-blade) But with more than one step, it might also be called a "Verzahter Hackenblatt" 

[D L Bahler]

My research has brought a few surprises. 

I assumed the advent of the wooden arch to probably be an American invention, or possibly German. I was wrong. 

It turns out that the wooden arch evolved over time from simple kingpost bridges in Switzerland. The earliest "Massivbogen" or heavy arch bridge, where the arch bears all of the structure, known to date was built in Switzerland over the Limat in 1766, with simpler versions of the wooden arch found throughout the country as far back as the mid 16th century. The kingpost truss evolved first into polygonal arches, and finally to true curved arches with the advent of the "Verzahnung" joint, or rather the realization (which the Germans appear to have never caught on to) that you can use this joint with more than 2 layers of timber stacked vertically. 

The same storm that flooded the Emmental in 1838 wrought havoc throughout Central Europe. Apparently this gave rise to some widespread misconceptions about Swiss bridges before that time, as the only survivors into the modern age of pre 19th century bridges are generally late medieval truss bridges. 

Here is a fascinating article. Even if you can't read the German, the pictures are worth looking at

https://www.ethz.ch/content/dam/ethz/special-interest/arch/idb/holzer-dam/images/Lehrveranstaltungen/Fallstudien/2017_HS_Bruecken/Download/Fallstudien_HolzBrueckenSkriptum.pdf

[Runningalucas]

Awesome thread!!!  I was enthralled with the Da-vinci bridge, and these are adding to my desire to build some sort of bridge on my land; somewhere..... I've got a pond I've been working on for a while, that would be neat to have a bridge over it!