Apologies for the low audio output on this video. We switched editing over to a new system and changed some of the ways we record audio. Unfortunately this led to lower-than-expected volume on the video output. Given the way YT works, it doesn't make sense to re-upload the video, but I promise to have corrected audio levels on all future videos. Thanks for watching!

I think they meant that people would be using this bridge for 100 years, but as a lesson, not a bridge.

A couple of things to point out: (greetings from Norway btw) - The old bridge was a single lane bridge and had to be updated to support two lane trafficking. (one in each direction) The choice of material fell on glulam combined with steel because of the weight limitations having to use the old bridge foundamentation and aesthetics. (NVE - Norwegian waterpower and electricity didn't want the river to be reduced to build new fundamentations) - The first bridge that collapsed, the Perkolo bridge (strange name in Norwegian also, almost sound finnish), was actually underdimensioned in the middle joint. It was bouild in two parts and joined on site. The two joints in the middle should have had 80-90 dowels, but it only had 24. Making the bridge only support 27% of the bridge planned capacity of 65.000kg (143.300 pounds). - After the collapse of Perkolo bridge all 13 glulam bridges was checked and there where some flaws in some of them. Tretten bridge was one of two (i think) to have recommendations for improvements regarding the joints.If I don't recall wrong it was something to do with the dowels. - The one thing that concerns me the most is what i have read in a master thesis written in 2018 after the colapse of Perkolo bridge with guidance from engineers in Statens Vegvesen (norwegian public roads administration). The different ways of calculating the stresses, the area to distribute this stresses and the general dimensioning of this kind of joint leads to widly different results. (The codes that are mentioned in the master thesis: EN 1995-1-1 (Eurocode 5 - Design of timber structures), NDS 2005 (North American Timber Design Codes) and a development sugestion for an improvement in Eurocode 5 from Statens Vegvesen.) For me thats kinda concerning, because it makes me belive that we don't have the greatest understanding of this kind of joint.

If you look at very old wooden bridge construction you will find that they would have inserted rectangular keys across the timber connecting scabs on both sides of the joints. The keys do not promote splitting of the wood along the lines of the wood fibers as the numerous pins certainly do. I supervised the fabrication of timber trestle bridges in the Army...we never had a tank end up in the gap. This was an outstanding presentation - thank you for sharing.

I live in Oregon, and we have a lot of old wooden covered bridges. The "covered" part is literally a wooden structure built over the actual wooden bridge to protect the wooden bridge from rotting under Oregon's rainy skies. The use of copper plates on top of this bridge's wooden beams looked shockingly inadequate, even for gluelam construction. However, Oregon's covered bridges have another interesting feature that this bridge lacks: steel tensioning rods. Since wood is not very strong under tension, the covered bridges use steel rods to tie the wooden beams together under compression. The steel rods take the tension, and the wood takes the compression. I'm not an engineer, but I'm wondering if the steel present in this bridge was providing enough compression for the wooden components.

The truck is being held by it's "pup" trailer, which is being stopped by the section of road lying on the river-bed. I don't think any tire could adhere the road at that angle.

14:05+ Drilling a series of holes one near the other is exactly how long lengths of wood used to be split. I've done that exact same thing building Inuit wood frame kayaks in the traditional manner and it's a very effective way to split a long length of wood.

This KZfaq channel is quickly becoming a favorite of mine. I'm a structural engineer and sometimes worry if my designs are safe enough, even if they strictly adhere to codes and regulations. This channel helps me learn a lot about how materials behave in real situations. Forensic engineering is awesome!

I "rode" suspended in a tender house on a bridge 2 days a week for 11 years, and noticed that any heavy vehicle, or one with a heavy load, pushes the bridge into a wave as it first gets onto the bridge deck. Additionally that wave compresses as the vehicle crosses. I cannot imagine any wood joined to metal surviving long-term waves like these.

I've used similar wood to steel connections in my construction. The one thing to double the strength of that connection is to have a steel compression ring wrapped around the area where the dowels are both located. And most definitely at the butt end of the wood where it directly touches the steel. The compression ring prevents the wood from splitting. Also aligning the holes in the wood in a half triangle shape (Arrowhead) with the point facing towards the wood helps reduce splitting instead of all holes in a line.

Great analysis. Regarding the truck and no skid marks, I believe the collapse was extremely fast and there was not enough reaction time for the driver to hit the brakes. Essentially the truck/trailer combination rolled backwards and stopped as the trailer bottomed out in the shallows of the river. This was very quick and not much gravitational energy was generated to jack knife the unit, therefore it stayed inline.

A new update today: "SINTEF has retrieved bolts from the river and examined them. All of the bolts have fractures caused by stretching/bending movement in the longitudinal axis of the bolts. There are no signs of fatigue or previous damage to the bolts. Overall, this indicates that the bolts have broken as a result of overloading when the bridge collapsed, the preliminary report states." They also show pictures of several rusty looking bolts that have completely snapped in two.

Yeah, my parents had to replace their balcony because whoever built it decided to put metal around the wood, so once water got in it held it there. One side had carpenter ants and was rotting away. It was VERY unsafe. It was sagging under anyone's weight, and was perilously close to collapsing.

The driver of the truck said that the roadway on the bridge suddenly looked like it had waves and then it was like an Earthquake. He had to remain there for a couple of hours until lifted with an ambulance helicopter. The driver of the other car could apparently get out herself and climb back to solid ground. Gudbrandsdalen is the valley, not a town.

Gosh, it's like we've forgotten the last several thousand years of timber building techniques and all the effort and clever techniques people invented to stop splitting wood beams under tension. Real Picard Facepalm moment ngl.

i life near the bridge i used it a couple of times( due to the near tunnel with roadtoll, i drive the more scenic road around it) thank you very much for the thoroughly analyses, as a carpenter this is quite interesting and informative greetings from norway

I'm a bit surprised they didn't consider this mode of failure.. until now I thought this is one of the most common ways that a DIYer learns that wood grain direction matters when choosing structural lumber.

A few random things occur to me: 1) The initial failure was at joint A on the A-B side. When this separated, the lower deck of the bridge dropped at point A. This caused a rotation counter-clockwise around the column support at C. Since the upper truss was still sound A-B-C, this put a huge strain on the upper and diagonal trusses C-D, combined with twisting the pins of the C end of the upper truss C-D. This caused the immediate failure of the upper truss connection. All that was holding C-D in tension was now the diagonal truss, and it then failed. 2) The truck has not rolled or slid backward primarily because the rear of the trailer has penetrated the collapsed decking and is now resting against the fractured edge of the deck and on the bottom of the river. The trailer is stiff, and so is the tow bar, which is now propping the truck up in it's current position. I would guess the truck was moving fairly slowly, and probably did not move backward by more than 2-3 feet, if that. 3) Since at least 1500, people in Europe have been building roof trusses and bridges out of oak timbers with rabbited and doweled connections. Up to the late 1800s there was a considerable body of knowledge on how rabbited and doweled joints worked (which is essentially what these joints are). I guess that knowledge has been lost. Also, when wooden wagons were constructed it was common to use iron end hardware on wooden poles. These poles were riveted to the iron fixings, in essentially the same manner as this bridge. But the problem with splitting at the pins was well known, and thus a cross rivet or two were installed to force the wood into compression around the pins. I guess this knowledge has been lost too. 4) While the idea of using gluelam with pins in tension on a bridge over a river gives me the shivers, I'm not convinced that this was a glue failure. The test specimens shown all seem to have been single timbers, and they failed along the outer pin lines. If the pin line was on a glue boundary, then glue deterioration could have contributed, but I'm not convinced that a glue failure was necessary to get this result.

I think the biggest mistake here was using wood to build a bridge to make it look like it was made of steel. Huge mistake. Wood can be used successfully to make a bridge that will carry a lot of weight, but it will look extremely different. If designing a wooden bridge, it needs to be designed to mimic the natural strengths of trees, and minimize their weaknesses. If you want to build a bridge that looks like a metal truss bridge, then use corrosion resistant steel with good quality epoxy based paints with several coats of primer underneath, and forget the wood. Using wood under the asphalt was to construct the bridge deck was another extremely bad idea. Every engineer should know asphalt paving always develops cracks over time. Then rain water penetrates the pavement, resulting in wet spots in the wood under the cracks. This results in uneven swelling of the underlying wood, creating more cracks in the pavement. Even if this truck hadn't broken the supports, the bridge deck would have eventually failed anyway. Like you said Josh, putting a bad waterproofing layer over wood isn't good, because once the wood gets wet, it stays wet, leaches out the treatment chemicals, then it starts to rot quickly.

Regarding the rusty steel, it's special weathering steel (Corten) made to get a thin layer of rust but it will put up very well in outdoor use without any paint.

Just come across this although it is a little old ...... Interesting. I work as a carpenter - some of it on structural frames (though not on this scale !). One of the basic rules that every carpenter learns and constantly looks out to ensure is observed is that "Wood can be strong in compression but is always weak in tension". You just don't design anything that puts wood in tension. These failures are something I remember demonstrating in college tutorials and practical experiments - that was thirty years ago. I've worked on glulam structures (smaller and less critical ones!) and spent time with the designer discussing how they have done it to avoid wood in tension. You just don't put wood in tension - it will fail. Especially under the effect of moisture, mould and time.

It's instructive to look at railroad trestles built in the 1800s. Steel was expensive and as little as possible was used. The bridges were primarily built out of wood, but they never let the wood be in tension, only compression. Steel (or maybe iron) eyebolts were used to keep the wood in compression. I built a model railroad bridge where they faked the eyebolts, but it at least showed all the places where the eyebolts would be, and it was based on a real railroad bridge. Of course, the pressure treatment equivalent then was creosote.

Keep in mind wood softens when wet, and end grain will allow deep penetration of water (that's how trees live). There is nothing but multiple points of end grain exposure in these joints. Also, all of the pins are aligned along the grain direction. It's basic woodworking to stagger them to resist splitting. I think it is unlikely this is a failure of the steel pins due to corrosion. The wood is more prone to failure due to exposure than steel is.

This seems to me to be the same stresses which led to the collapse of the I-35 bridge in Minneapolis. In that bridge it was failure of lower chord gusset plate and rivets. Analysis demonstrated that thicker steel was needed for the plates, with more rivets. Weathering was also a factor. Wood structural elements under tension fail at the end-attachments, as you have demonstrated very nicely. Thank you for this excellent analysis, explanation, and demonstration!

I designed and built a bunch of small bridges in the 1980s and early 1990s. My oldest glulam is now 37 years old. On bridges with good abutments and an under 30 foot span, glulam was the best solution. I had all of my glulam pressure treated with creosote to 12 pcf retention. I was in the middle of a bridge project in 1991 when I was called up for Desert Storm. When I got back, it took the road crew 5 1/2 hours to install a glulam kit. That saved a lot of money. Another good video. 50+ years ago we used shear rings in connections. Bearing failures with wood are usually a slow progression from repeated loading. It sounds like they can't believe that the software is wrong. I have to wonder if post-tensioning the wood to steel connections is going to be necessary. Good Luck, Rick

Something came to mind very quickly looking at the pinned connections. The designers seemed to be going for something like a pinned box joint or lap joint (to borrow a term from woodworking). However, the pins were positioned between lamination layers while the fingers were perpendicular. This is exactly opposite to how you want to set up your connection! The pins should go perpendicular to the lamination to anchor in as much solid wood as possible. The plates would then be coplanar with the laminations and have much better contact surface. They went with an incredibly weak connection that would also weaken the wooden members themselves. In addition, the leverage of those pins through the weakened members would then peel them apart along the glue. Another thing is that laminated wood can be very susceptible to damage from humidity. The splintered deck looked like MDF or fiberboard that got wet. You never use those outside. Edit: Watching the video further seems to confirm some of my suspicions. Also, around 22:50 you're talking about the connection failure mode(s). I think the paper is trying to say that because they didn't properly account for deformation of the connections, the actual loadings differed greatly from those of the models, hence they overestimated strength. It comes as no surprise that the connections tended to split the wood. That's the primary failure mechanism for any wood joint. Ask any woodworker and they tell you that splitting is the number one concern in any connection because weakest direction is perpendicular to the grain (i.e. the lignin holding the wood fibers together). You almost never see a connection fail across the fibers, hence why pinned joints always need plenty of material outside of the pin. Also, any good wood joint uses glue on all of the faces. The pins are never the primary holding force. It's the massive surface area contact between pieces. I don't see that at all in the steel/wood connections here.

One idea is to have the wood grain in multiple orientations, at least where the bolts are applied. The beam itself can still be lengthwise along the grain, but at these junctions there needs to be fibers going in more than just the lengthwise direction. Also, compressing the wood to squeeze the fibers together might be another helpful option - so that the fibers don't have room to part.

Just for accuracy ;19:00 no error in translation here, it is exactly as it is written . At the beginning of the loading, the timber hole increased in size to the point where the wood was broken by tension perpendicular to the grain when the bolts acted as wedges and separated the fibers along the grain by that perpendicular force exceeding the strength of the links between fibers. You can see in the picture the wood is split and open by forces perpendicular to the grain not that it broke perpendicular ,the tension is perpendicular.

Glue lam beams are a strong building material, until they get wet and stay wet , especially the tension connections I had a structural engineer tell me once when he was designing a job for me “ it’s always the connections that will kill you “

I have over 20 years of experience as a framer of custom homes with basic math skills. This design gives me the chills. Excellent presentation, as always.

Very odd that these lovers of wood (I am a wood lover too!) don't take lessons from a bajillion years of carpentry and instead try to use wood like it's a homogenous metal

Interesting to see students and engineers learning things carpenters and woodworkers have understood and discussed for centuries

it appears that pre-tentioned cables (like the ones used to hold box girders together) would be a way to retrofit any remaining bridges that have trusses built in this manner

After that collapse on Aug 15, 2022, they closed FOURTEEN other similar truss bridges! Looks like they bet big on glue lam and it came up snake-eyes.

If you have a chair that has crossrails that are mortise and tenon with a couple of nails through the joint, then rock back and forth on the chair, the joints will loosen, and eventually pull apart If a simple woodworker can understand that, why couldn't professional engineers !!

Fantastic video! I really like technical engineering videos like this, and you do a great job of explaining things in an easy to understand manner. Will definitely be checking out more of your content!

Glue lams are very common in residential construction, but generally don't have vehicles driven over them, nor are they exposed to weather, wood and weather not exactly being the best of friends (the old wooden railroad bridges were made of solid oak beams soaked in pitch). Also, where wood and steel meet, generally the wood is "wrapped' by the steel and bolted though the wood and the steel, or at least large washers are used on the bolts to help compress the wood (wood does love to swell and shrink, especially in harsh weather conditions).

15:45 ANYONE who has ever worked with wood could have told them that is how wood is going to break.

When they sat "tension perpendicular to the grain" I believe they are referring to the axe head effect that is taking place between the bolts and the wood. The grain is put into tension as the bolts are pulled through it causing a splitting action rather then the wood pulling apart in the direction of force.

I'm impressed how well the glue laminate kept the water out When you said wood my head went straight to "what happens if the wood soaks in water then freezes" but it seems to have kept it out quite well

Boatbuilder and wood-engineer here. When I was in my lab-phase in uni back in the nineties, I initiated some tests of all-glued multidirectional connections in comparison to these metal-multidowel load-bearing connections because we had, obviously, exactly that form of malfunction (splitting) every time we tested dowel-patterns and dowel dimensions. As a trained boatbuilder before I started university in wood-technology, wood in connection with changing water/humidity contents thus changing dimensions in all three deciding dimensional directions differently was someting I had in mind automaticly whenever looking at a connection point, as well as the idea of "how gets water in, and how does it get out again"? What I built in testpieces from "cheap, inferior" wood (fir/spruce, construction grade only, no tropical hardwoods, not specially sorted/improved) basically followed the wooden dimensions of the customary connection wood/steel, while I glued everything, no holes, no slits, no cavities, with changing directions by overlaying different directional wood layers, glueing those into one inert lump of wood like a grown tree crotch, thus creating the directions, dimensions and the number of pieces/"load outlets" we wanted/needed for the very detail. Results in comparison to inferior wood-steel connections with pins were stunning, to say the least, not only in wood/epoxy with vacuum pressurized curetimes, also for "conventional" resorcin-formaldehyde glue under vacuum, pressurized for its reaction time, the latter to circumvent the not-yet finished research for "creeping" in epoxy glued connections in wood over time. "Too specialized", "not doable in situ", "not repeatable enough over a three month build for hundreds of joints" and so on was what I heard by many many professors and pros from the building industry over the time I tried to "implement" a bigger research project, because they all simply were not able to imagine something like a big construction from inert, multidirectional, multidimensional glued wooden limbs with glued, inert loadbearing connection points ("load knots"), built and finished in situ, of course. Our university's administrative building even was a gluelam-metal-dowel steel-knot building with a lot of visible failing points, some of those failing already in the building phase, in the most pittoresque manner, which would have made my uni the absolute prototype to try something completely different, some never tried-before fancy ideas - they couldn't even understand it, let alone actually try something different. My fellow students and I, we developed industrialized CNC-routed storey-high dovetails for timber-frame housbuilding with prefab elements to put those together like Lego on the building site, we put together a prefabbed three-bedroom family home in a day including the roof that way, with ten people and one crane as a prototype and test-piece - still not widely used in the industry to date, despite its many benefits for structural statics and physics. Them woodheads wanna nail things together like they ever did. Where I had learned as an apprentice in boatbuilding, we did all kinds of fancy repairs in the field under vacuum with epoxy, wood-only as well as carbon-glass composites, wood-glass composites, sandwich and massive constructions, partly even with special heating for the glue joints only in subzero (celsius) temperatures to make sure epo cured properly, especially needed with carbon prepreg of course, and "not doable in situ" never ever was the reason it failed, if our repairs did fail at all ... usually the next failure was in the neighboring original material. My master, mentor, employer in that apprenticeship had a deep disdain for engineers for exactly that reason of their extremely confined imagination and their even worse lack of "balls" when it came to trying new solutions once the traditional approach repeatedly failed. It became pretty obvious for my why he thought so when I started to deal with my profs and their donors from the building industry.

This was interesting. I just a dumb old carpenter from Maine. When you frame a building and are using plain old fashion planks as beams, you lap the joints to help hold everything together. Look at 200 year old barns. Yes, they were post and beam not planks laminated together, but where 2 beams meet on a post, they are half lapped and doweled, not just butted. I have seen pinned joints in many construction details, but they also have a bolt running perpendicular to the pins to hold the wood together. Some of these joints are over a hundred years old.

“..He turned the front wheel- he or she- whoever was driving that..” 😂 he OR she? 🤣 👌 good one!

Okay, I have to say, I love that you give the full explanation. It's not just "here's the simple version". You consistently deliver relevent background, detailed information with laymans explanations, and then a solid conclusion. The time taken to explain why you drew the lorry where you did is a perfect example of what makes your videos work so well.

I highly suspect water damage at the lower connections. I understand the deck was paved with asphalt. Where does all of that runoff go? I suspect right to those connections.

Ten years is an interesting failure time. Wood typically fails through significant creep at around 1/3 of the ultimate momentary stress in a decade. Elasticity also MATTERs. If your wood cannot load ALL the pins equally (which requires matching the stiffness of the steel perfectly). These two factors can work together to lead to unzipping over timescales of a decade, even in the absence of glue deterioration or moisture. Moisture of course makes creep worse a _LOT_ worse.

Subbed! This was an EXCELLENT breakdown of currently known information on this unfortunate (and likely avoidable) incident.

great work, thanks. Your thorough descriptions assisted my understanding

As a civil Inspector retired after almost 50 years it has been my observation that design Engineers tend to blame deficient materials, fabrication, and construction for failures. They dismiss the design as the cause because of liability, and insurance and bonding.

When you say, “It’s seems very strange to me.” That’s an extremely polite way of saying…, “I can’t believe how GD stupid they were to do such a thing.” And IMO… you’re not wrong.

Some things to consider as possible fixes: 1) A tight wrap/sleeve (that CAN'T expand very much) around each doweled joint to make it much harder for the wood to fully wedge apart. This way, the dowels themselves would have to shear or the wrap would have to explode BEFORE the wood can split across the wood grain. If the wrap were made of thin steel (arbitrarily,

Anyone who has ever worked with wood, knows it works best in compression, not tension - and this is even more important if the wood is expected to get wet (especially saturated for long periods of time). Even cantilevers have to be done with exceptional care. There's a reason headers over a door or window will be 12" tall when the jack stud supporting it might only be 3.5" on the largest dimension. Much like single direction carbon fiber, wood has a very different strength with and against the grain due to the bond of adjacent parallel fibers versus the combined stregth of those fibers in tension endwise. This is why plywood is designed with various angles of grain in-plane with the sheet, and carbon fiber intended for mutli-directionla loads has a cross weave and additional layers in the correct orientations. It's also why we put fasteners through the plywood perpendicular to the plane - with the in-plane crossed grain, one layer of splitting would put the next layer into tension+compression. Chip board aka Oriented Strand Board (OSB), is like taking plywood to the completely random grain orientation limit. If they really put their pins through the glue-lam parallel to the glue layers - IMO they should just be sacrified on the alter of license revocation for other Practicing Engineers to see as a warning against using materials they have no experience with, without an exceptional amount of due dilligence (not just reading a few research papers and copy pasting unverified numbers). When wood gets wet, the fibers swell and this parallel adjacent bond is even sketchier - and some of the detailing they did on that bridge with the copper flashing, looks - well suboptimal I'm going to say diplomatically. A lot of that flashing appears to direct shedding water INTO the joints where the strength would be most challenged by removed fibers to insert the fingers.

I know nothing about engineering, although I’m pretty good with Lego’s, but I love these videos. They are always fascinating and well presented.

26:00 the rear trailer is on a part of the deck that bottomed out. It is now a deadweight anchor. I believe there is water inside the trailer box. The pulling beam is actually holding the truck in place. That is why the truck did not skid downwards. The aggregate on the truck DID slide down.

It is likely helpful to remind people working with wood that a transversal dowel always is a wedge and thus very good at splitting the wood. To properly use the properties of wood the side bars of the bridge should have been dual overlapping segments so that loadtransfer would primarily been via a contriguous connection next to each assembly point. Doing it like that had probably doubled the pull load capability that the bridge failure seems to be the result of. Strange that all they knew when building dragon boats with their incredible hull strength has been forgotten .....

Thanks again for another wonderful educational video. Your analyses are always excellent. :)

One retired bridge engineer from statens vegvesen who worked certifying Tretten bridge said in the media that he thought the collapse came as a result of different thermal expansion of the wood and steel, causing the wood to crack in the points where the two met.

In Australia, that 'double truck' is called a 'tipper and dog'. Its called a dog trailer because it follows your truck like a dog. Also a dog of a thing to back up until you're used to it because they're short.😉👍🇦🇺

I'm a BIM Coordinator for a structural engineering firm and the second I started this video and heard that there was glulam connected to steel I immediately thought: "Oh it's gonna be a connection failure, probably with some water intrusion." I feel like anyone with a basic understanding of materials should have known that this was a bad idea.

One point: You *CAN* make a GlueLam arbitrarily long, by staggering the ends of the constituent boards. You can then upsize the beam so that there is always sufficient contiguous wood fiber at any given point to carry the entire load, and then make every non-end joint run continuous. The problem is that you can't *transport* an arbitrarily long gluelam - you'd have to do the lamination on site - and then you'd have to do all the assembly in situ at height rather than safely on the ground. These two things make your cool inexpensive building technique into 'The steel bridge won the bid'.

What immediately jumped out at me was exactly as you also noted, why was the bottom lamination horizontal instead of vertical? I really like your analytical logic. Thanks for another great video.

Anyone that has spent any time building and working with wood would tell you that was a bad idea. It could be designed much better using similar methods IE you would have to have beams that overlap the joints as the end connections have no real strength over time. And to do those joints somewhat decently you would have to wrap the end of the beam in basically a metal tube to constrain it so when the wood splits it has nowhere to spread. I used to play with pinned joints etc playing with ideas of construction when I was doing lots of woodworking but in the end the only reason I was doing it was to come up with a cheap way to get something usable and no it would never last in the long run. All those saw cuts for the plate joints invite corrosion and water intrusion where it will freeze and expand and break the wood. Lots of other issues that would take too long to type out but needless to say the woodworker side of me says run away from that project. Clearly the engineering company didn't have people familiar with woodworking or consult anyone. A quick call to a few ship builders would have answered their questions really fast and changed their minds.

Amazingly detailed analysis. Very interesting! Thank you.

Love seeing the beautiful original column and abutment, completely unfazed.

Great video. Never knew your channel before Surfside but glad to see you covering engineering failures. My favorite topic. I too work in the industry but have zero motivation to make videos. Sometimes i wish that wasn't the case but i just can't get into it. Glad you did! Great video great content as usual and great speaking voice and cadence. I've been a fan and will continue to be.

Especially in winter weather with the roads being treated for snow & ice plus the constant splash of the river. Any wood held together with glue was doomed. Treated lumber 🪵 rots. It just moves as a slower steadier pace. Great analysis Josh!

Nice detail presentation again 👍Think this is gonna be my new favourite project to follow.. loved the Surfside series.. cheers 😎

When I saw your diagram, the first thing I thought of was mass produced house trusses where the 2x4s are butt joined using plates and nails just like in the bridge, only smaller. Watching those things wobble, bobble, and flop when being installed, I'd never trust that to hold in a member exposed to weather and dynamic loading.

There was a reason that wood bridges are covered bridges. The bridge would have failed covered or not. This bridge should never have been built. Engineering is at fault.

Around here, there used to be many steel truss bridges. Every single deck was made of wood covered with asphalt. They were all very old. The difference? The wood was large monolithic boards. 3”x 14” or so. Single 4’ boards from old hardwood trees. They were attached together, but not to the bridge. The deck just floated. They had to remove them due to the inability of big truck to go through them, not because they were bad. The good thing is all of them were salvaged repurposed out west somewhere. It was very impressive process to watch when i was young. Huge equipment and big trucks. Nirvana for a ten year old boy..

Josh; find your analyses thoroughly engaging, even though it's nothing to do with what I do for a living or in my hobbies. Thank you for the content you make.

Protection from the weather is a good point. One successful example is the Superior Dome in Marquette Michigan. It is an all-wooden dome that is sealed from the weather and has held up well.

I am pretty sure that analysis engineers pointed out many things that you said during this project. All of this seems quite obvious to me. The recurrent problem that I have in my job is to stop my boss to cling on any good result that would make things cheap, and neglect any warning that I have on the limitations of my simulations.

5:04 We call that a combination 4-axle rigid truck and two-axle (dog) trailer in NZ, although few people outside of trucking would differentiate between a dog (articulated) and pig (simple) trailer. I wasn't aware Norwegians used 'lorry' - I actually thought that was exclusively a UK term. You can learn something every day, if you're paying attention.

Maybe there is another thing to consider (I am not a construction engineer / architect though, so if somebody knows how this is considered/calculated IRL, let me know): When the connections are made IRL, there is not only the tension in the direction of the truss itself, but there might also be a torque component from the load of the bridge. I would say this torque may greatly increase the chance of the wood splitting. When you show the interlinking of the fingers (12:50)... try squeezing the fingers hard and pull the hands apart (it's not that easy). Then try the same, but with the hands twisting. The twisting action of one hand will open the fingers a bit and it gets much easier. That's what might happen with the wood as well. If the dowels apply some torque, they might be opening the wood grains. Wouldn't it help to have the joints wrapped in tightened steel hoops to prevent the opening? Edit: 35:30-ish - the way you drawn the two truck beds around point A is kind of consistent with my theory. If both objects are pushing the bridge down around point A, the two horizontal trusses experience opposite torque, meaning the bottom A want to split open. If it wasn't one piece of wood, but CJ like on the top, that's it. Also, the top A (32:02) shows result of torque (although that might be result of the already-falling bridge after bottom-A failed.

For hundreds of years ships were built of heavy wood members which had grown in that shape. The builders knew how to join planks to ribs that were expected to withstand heavy seas for decades.

You have a real knack for explaining these things in detail and in just one take.

There is a large historical N-truss wooden bridge near where I live. The ends of the beams which make up the trusses are surrounded by steel casings and I think the joints are steel. So the casings help support the wood and prevent splitting. The truss structure is also a straight design. The bridge which collapsed has sections which vary in size which looks pretty, but compromises the strength of the truss. The unsupported length of the Norwegian bridge is also very long. I wish I could post a photo of the historical bridge here, but I'd have to make a video. You spoke about splitting along the laminations, but I don't think that the laminations run that way?

I think the diagonal piece between A and B would have been in compression in this instance, at least whatever proportion is carried by the new steel columns would have been carried in compression there. All the diagonals are slanting the same direction, so they can't all be in tension.

Great analysis. Keep up the good work.

Wood will absorb water. That water then makes contact with the pins in those connections. Bad things then happen. Boatbuilders know better than to use ferrous metals in construction - they use bronze if the boat is intended to last. And never, never put wood under tension.

I'll nitpick a tiny bit - the "wind truss" doesn't just transfer wind loads to the other truss. It's adding moment rigidity in the horizontal axis because it is a truss. If it was just beams straight across, it would load share horizontal loads.

Looks like a bridge I'd make in Poly Bridge 2, praying as the heavy truck crosses it.

Great report. Fascinating.

36:40 every treated lumber I’ve worked with only gets the treatment to the exterior of the wood. Nothing makes it into the center. I’ve seen treated posts rot from the center out.

35:00 -- "The Lorry and the Load"... Sounds like the title of a bedtime storybook for parents who want their children to become engineers 😂 Seriously, though, great video. I really enjoyed your analysis and explanations.

30:14 what you want there is a gusset plate on each side spaning that point and some sort of screw or thermal mechanism to tighten it to pre stress the wood on bother sides a bit

Something about those construction joints reminds me of the classic Kansas City hotel bridges: for practical reasons a joint was modified that subtly changed the load path. Different details, maybe assumed in design, before value-engineering, might have worked well.

Your analysis are always amazing. Just wanted to say that there’s also a noticeable ideological trend in the building industry when it’s about “ecological” materials. Sometimes some people (not all of them) seem to have unplugged their brains when those materials are involved, and they sometimes lack basic thoughts a professional should have (not saying those materials don’t have great properties). Some examples: vapor transfers through building envelopes, insulation an OSB, energy consumption for fabrication of materials… Heard a professional years ago saying he didn’t need to consider the wood wool insulation in its CO2 environmental impact calculation because it was an “ecological material”, which everybody who knows how much energy this requires to dry out the fibers will find silly… Ideology is dangerous, especially in engineering!!

Yeah! Thank you for all the knowledge you teach us about. I appreciate learning. Even at 63. Peace my Friend 🌈🌎💞

I just wanted to say one thing... This comment section is so polite and filled with hi-end data that feels like those old good technical forums. So nice.

Beautifully analysed and described!

3:50 you can see the tag along trailer is right over the split so the bumper is on the pavement and the wheels are probably in the air so the trailer is wedged and holding the truck from moving.

I’m not sure if you’ll see this or if it matters, but is it possible to have a yellow line instead of red over pictures on screen? I’m not sure if this can be done but as a colourblind person red is essentially invisible and I’d love to follow along lol your videos are very interesting

Really interesting, watched the whole thing!

25:42 i tell you what im impressed by .. that road bed ... the fact that the road bed under that truck survived the shock , acceleration jerk and deceleration with that truck on it and still being in on peace

Got to say that one of my first thoughts when i saw the design of those joints was - how can they hope to control rusting of the steel and pins? And we all know what rusting steel does to concrete, does not take a lot of imagination to think what the steel that slots into those joints will do to the laminate when it starts to rust and expand. Surely it's going to force those laminates apart? Rust will start to jack the laminates apart where the steel slots into the wood, and rust from the pins will not doubt accelerate the wood splitting along the grain. A recipe for disaster on it's own.

Reminds me of the Miami / Florida International University FIU bridge collapse.. they had to go the "creative balancing act" on that one collapse.. could have been a standard bridge but Politics and $$$ always wins!!

The bridge engineers rigorously tested this design in Poly Bridge before deploying it into the wild...

There is a report out today with the conclusion of what happened. It was the leftmost column that gave in, but in the same manner as you concluded in this analysis. In 2016 the authorities was warned that the bridge was underdimentioned, but they did not follow up on the information.