How Did the Engineers Miss This?
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- Опубликовано: 27 сен 2024
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#BuildingIntegrity #tretten #trettenbridge #bridgecollapse #glulam #construction #engineering #tension
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Understandable! Things happen. :)
Seemed ok on my end
So ... wood trusses didn't hold up as expected? 😆
pig 2 would know this does not work
Perhaps new math and new ideas should not dismiss old school logic.
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.
Thanks for the background info.
Do you know of an English version of that thesis?
Thanks for the information on the other design constraints that are missing from this discussion. Sadly, they result in bad engineering outcomes.
And thanks Ruben for the comment. Understanding how something failed is nice, but it's also important to ask WHY someone thought that this was a reasonable approach in the first place. To do that, you need to understand the constraints they were working with.
So basically the power company is to blame
I think they meant that people would be using this bridge for 100 years, but as a lesson, not a bridge.
This made me laugh 😃
I am reminded of the bridge failures using cast iron, in the mid-Nineteenth Century. cast iron is brittle, excellent in compression but not in tension and subject to fatigue cracking from badly machined holes, casting defects such as blow holes or 'cold shuts' and even unnecessary decorative features such as mouldings on the iron work.
@@johnjephcote7636 …..
In the 19th century they didn’t have computer modeling or the benefit of the amount of experience we now have in building bridges and other structures.
If you’re suggesting we’re making mistakes with New materials now, as they were making mistakes with New materials then…., well on the surface…., that does seem to be true. However we have much less excuse to be making such mistakes these days.
@@mercoid Maybe a good lesson that computer models can't do everything, us engineers still need to analyze our designs ourselves - especially for new materials.
@@positivepenny5477 material is not new and there has been bridges made out of glulam for decades but i think making same kind of bridge than steel bridge was is the main problem here, designing it differently just for glulam should be all right bur trying directly to replace other material and not changing much design was the problem.
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.
Not anyone with experience here just curious. Would it make sense to change the dowels to squares/rectangles to reduce the wedge action?
@@_aullik think of it differently. Wood is fibers. In this structure used similar to rope fibers. Now imagine the same structure, wood fibers replaced by steel cables, attached with the same pin arrayed into the terminal end of the steel fibers with nothing to hold them into place except the rate of material fatigue. Just a pin placed into a fraying rope end, nothing to stop it unraveling.
I was thinking something similar while watching this video.
Actually, would it be possible to perhaps use compression alone to hold the wood in place instead of any dowels?
Or mostly compression?
@@Luredreier That was my thought too. Generally this sort of connection in many designs rely on friction only, the bolts are there only to maintain proper pressure and friction. This could also use all of the methods. Those sheer bolts could also be put on tension and apply friction between wood and steel, then another bolts welded into metal plates on the other sides to prevent the wood from splitting.
This exactly came to mind as well! Think about how the handle of a hammer or an axe is attached--those joints are highly robust. The steel head acts as a compression ring in that case, and that joint stays in place without any pieces undergoing direct shear.
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 was wondering why the pins here were going across the fibers as opposed to along the fibers. Makes zero sense.
@@SonicBoone56 I recently secured a demolished barn allowing workers to do cleanup without getting injured. I used long two by fours as columns with scabs on both sided creating short columns from slender columns. I simply bored one inch holes through the interface between the columns and the scabs and inserted hard wood dowels to supplement the connecting screws. It worked fine and was a lot easier than routing for square pins and getting effective alignment between the pieces.
Yeah the moment I heard "glued and laminated sheets" and "bolts through it" it was clear what happened. I see the same thing when I drill through planks or rods with hand tools.
Would it make much difference if the joints had bolts instead of dowels compressing the entire cross section of the beam such that all fibers are effectively secured?
@@RobertDerusha Bolts might be better for a while, however wood has a nasty tendency to change dimensions when exposed to water. This change can be slowed by surface coating...paint being far more effective than very pretty varnish. The change is most prominent along the growth rings (not a problem here) and across the growth rings (less of a problem in this application) and not at all along the height of the tree. The objective should be to place the adjacent grain fibers in shear by providing sufficient length between the "across the width" fibers and the exposed end of the wood or between successive rectangular keys.. That's how it was done in the old days. Screws impeded in the ends of the timbers might be somewhat effective if they were very long and of Buttress Thread configuration. Otherwise the would tend to split the wood like the patented log splitters using a tapered screw. Tapered Buttress thread screws might work but I don't hold out much hope for screws in the end grain...always avoided in classical woodworking. A drilling and taper reaming operation would be necessary for effective installation.
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.
Not sure what part of Oregon you are in, but there is a modern version of a covered wood/steel truss bridge in Clark County, WA (near Portland) called the Cedar Creek Grist Mill Bridge. It was designed/built in the 1990s.
that was a very interesting comcept
a balance between compression and tension
I think you mean to ask if there was there adequate steel to carry the tension load.
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.
I would agree, also the fall of the truck was pretty dynamic, because the truck was surely moving even while the bridge very unexpectedly collapsed, so the truck must have fallen and landed almost like somebody would trip upwards on a set of stairs.
@@MrSaemichlaus The driver was most fortunate. A fraction of a second either way could have killed him.
Celebrate good fortune.
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.
I made essentially the same observation.
I too concur. The rear axle of the trailer is likely jambed against the deck of the section behind, and having moved only a short distance in reverse, the drawbar of the trailer wasn't subject to much greater loads than just the mass of the truck and its shingle load.
Don't forget ABS brakes.
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.
or triple airplane xD
This was my thought. Wood workers around the world know that wood will split along the grain.
@@jasonadams7308 Especially if you drill lots of holes in it and align them along the grain ! This could not be more brain dead if they tried. But their principal aim is the "save the planet". All else is secondary. CO2 impedes proper brain function !
Lol, yeah agree. Humanity never learns, unfortunately.
That is exactly what I was thinking. My favorite homes are timber frame, everything in timber framing has pressure (probubly the wrong word, I am a desiner not engineer) on to each other to the load. Then they use metal brackets to join everything together.
Even at my level of knowledge (or lack of knowledge) I know to offset nails or screws so distribute to weight and I don't split the wood.
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.
We used to call this a bow wave. Happens to asphalt on a insufficiently compacted surface also.
Happens on ice even quicker. Ref:ice road truckers you can see and hear it
Im a trucker and in the US this isnt unusual. Big heavy concrete bridges and you can feel the bridge react. Then a second truck comes on and it gets..a little worrying. We actually have laws determining how close together our wheels have to be adjusted because of this
@@jgren4048 That's why there's strict speed limits for heavy loads on ice roads: it allows the "bow wave" to spread out and weaken before the mass of the vehicle reaches a portage to go on land. If the truck is going too fast , the energy can literally cause the ice near the shore to blow out. It can also happen if the water shoals quickly in the lake and that bow wave and the truck hit it.
My very thought. The bow wave was stopped at the point of the new support columns. Failure probably hadn’t occurred under the loading of the truck/lorry alone.
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 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.
I think you have a really good point about how wood just needs a different design. Just look how much weight wooden train trestles can handle!
The High Level Bridge in Newcastle-upon-Tyne (England) was built 1847-49, supporting a road and pedestrian walkways under 3 rail tracks (later reduced to 2). The roadway was asphalt over a timber deck.
From 2005-8 the bridge was closed for restoration, which included replacement of the original 150 year old timber road deck with new timber. The bridge still carries two rail tracks, and the addition of safety barriers (and weight considerations) reduced the roadway to a single lane for public transport traffic only.
@@robglenn4844 Always in compression. See my explanation elsewhere about the terrible geometry of the truss design they used here.
A really good point, and very true. As an aside, for people that may be don't know, the first Iron bridge in the world, at Ironbridge in the UK, was built and designed largely as if it were a timber bridge, sort of squaring the circle.
@@hypergolic8468 IIRC it was actually very much 'overbuilt', wasn't it? Luckily for us, as it's still there. And it's a beauty too. But it was cast iron, later discredited for bridge design in the railway industry, after some nasty failures- cast iron being okay in compression, but not in tension, so in that way, maybe more like wood, making the Ironbridge design very sensible if it was built as if wood? I ask pretty humbly here, I'm no structural engineer, so please do correct me if I'm wrong.
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.
ב''ה, I think common classical techniques included sealing with pitch, bitumen, whatever emmymadeinjapan made her turpentine potatoes with - it's shabbos, I should at least be studying something else rather than this - and later the more toxic creosote. If data on treated connections isn't available, I guess that's more work to be done later.
Still trying to comprehend the actual failure here, but would simply pouring a hot tub of pitch into the pinned connectors have bought much more endurance?
@@josephkanowitz6875 I doubt it.
@@drooplug Same here, the wood is still moving with load, absorbing water, freezing and so on. Stagger the bolts, extend connections with a cinch plate and install a compression ring. That truck w/load is too much weight for a wooden bridge. I'm sure it was fine when new but wood degrades when exposed to the elements
What happens to wood when it freezes? Or freezes wet?
15:45 ANYONE who has ever worked with wood could have told them that is how wood is going to break.
Seeing that nearly killed me. It actually looks like a person who has never picked up a drill or a chisel designed and built a bridge alone.
@@johns1625 And probably never split firewood. If you hit the wood correctly with a splitter, it's very easy to split, and stack it up for winter :)
And 2000 years ago, they would not have had a load that heavy, creating 12 point loads (on 6 axles). Well… unless they were rolling an obelisk across a bridge.
@@sambrusco672 I'd always bemoan the "glued together woodchips" that americans call houses and go up in flames or hurricanes like matchstick houses but I guess we're not much better in Europe with our upscaled glued together ice cream stick bridges
@@sambrusco672 I was talking about the specific failure modes of the peg and groove construction. I dont think this style of construction 2000 years ago. But people 2000 years ago would also tell you that wood will break along the grain.
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.
Any encapsulated wood Is liable to retain water and rot
As we develop new technology, we forget the old technology. I believe this is partially because the new technology is in computers, and the old technology was in books and minds. A great deal of the old knowledge needs to be entered into computers properly so we are not taking two steps forward and two steps back. And libraries need to not throw books in dumpsters because they have not been checked out x number of times in an arbitrary time period. Especially when they have many empty shelves. Take care.
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
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
Not only that they "use it"... they modeled wood as an homogeneous material and wondered at the results of their blackbox garbage in-garbage out simulators. I bet they were pretty color plots and curves, very convincing!
They may be standing on the shoulders of giants... but they have their heads firmly up their own A**
It's crazy how this happened despite engineering, past anaylses, and so much history to draw from. Glu-lam is not bridge worthy. 🤦♀️
there is nothing wrong with that as long as they would've used the amount of material needed to support the expected loads, but obviously economic considerations won't allow that because the cost of construction would be the same or probably even exceed the costs of a full metal bridge and the project would absolutely lose its rationel due to the shorter life of use
💯
@@heateslier That is the lesson that they should have learned, yes
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.
Dumb design - first to take away wood for the fins then to further weaken the wood with multiple holes....Who designed this?
Also for splitting rocks.
If I ever drill holes even close to the end of a wood board I'll always add Stainless Steel bands torqued appropriately so the wood can't split.
I've never had a board with SS bands split. I wonder why I never see the method used on any projects.
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.
They probably have drainage pipes to get rid of it between the beams, not onto the beams and joints.
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.
Wrought Iron was doing that 100 years before Corten was ever invented.
Corten has... issues. In some applications it can work, but it does not handle standing water well, so you have to design it to avoid corners/etc where water can accumulate. Such as, say, wind-driven rain forcing water in between the steel and wood of a joint and then sitting there...
@@Hammerandhearth _Wrought iron was doing it, before it was cool. But you've probably never heard of it._
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.
Good point. Whoever designed this bridge also did not understand the far-out elasticity of steel under load. As a consequence of the steel deforming a lot under tension, all the load goes to the short span of glulam between the bolts and the butt end of the glulam.
Moisture? No, wet wood does not decompose if it remains wet, because the decomposing organisms require oxygen, which won't be available. So, you need "dry-enough" for fungi etc. to attack wood.
concrete is the same - good in compression, terrible in tension. Reason why you put steel rebar in concrete structures.
I'm going to disagree with you. Wood is incredibly good under tension. What fails is the fasteners into wood under tension. Of course, although wood is much stronger than steel per weight of material, it is subject to rot. I would also be very careful about mixing steel and wood in a structure where heat cycling is concerned. Their relative expansion due to heat needs to be carefully considered.
This is complete BS. Wood is not weak in tension. It is stronger in compression parallel to the grain than in tension parallel to the grain, but the difference is generally in the 10 - 40% range depending on species. A specie with 2,000 psi in compression parallel to grain may have 1,400 psi in tension parallel to the grain. This is still substantial capacity in tension and wood loaded in tension “won’t always fail” as you claim. It will only fail it not properly designed for the load expected.
Steel, wood and concrete are all useful materials when properly designed and used. The issue with this bridge failure isn’t the material used, it was almost certainly improper design and/or construction. There are many wood bridges in the US today that are well over 100 years old.
@@LTVoyager Good old creosote!
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.
Anyone who has ever worked with wood knows that grain is strong in length, but is very weakly 'glued' to adjacent grainlines.
And oh gosh could they mangle the language trying to sound technical here. I literally did not get it until this chap unpacked their meaning.
Thing is: my very first structure lecture in 1973 was on the merits and downsides of timber. And the very first point made was this exact fact re grain.
Whoever the architect was on this project must have slept through about 40 lectures.
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.
The first ten years of my engineering education came from Lego! Modeling at scale is an important part of classical design, and Lego's offerings of couplings and parts are designed to teach principles. If Technic doesn't intimidate you, you may be more of an engineer than you think!
I bet a solid Lego bridge would hold up better than glulam anyway. :p
That's a good example you made with Lego's. Put some pieces together, and they can support an incredible amount of weight. Anyone that has kids and lego's scattered over carpet knows what I mean! But give those Lego's a little tension and they pull apart very easily, just like this useless bridge...
@@jercos In compression yes, but not in tension. Lego's are designed to be easily pulled apart and used again to build something else.
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.
There is horizontal AND vertical lamination in those beams, because they are all made of relatively small wooden bars.
@@comettoPL Wow!!! Even worse!!!
I would assume because the glue is stronger than the wood.
@@straaat nope
@@straaat In many cases, the glue is stronger than the wood. Thus the wood fibers can tear instead of the glue bond breaking.
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.
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!
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.
With the pins not being sealed, would make a high way to bring water in to the joint and the freeze and thaw cycles can go to work. also if the glue does not expand and contract at the same rate as the wood this can/ will accelerate the unzipping
Interesting coincidence--the video I watched immediately before this one talked about Quetzalcoatl.
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.
Yes, the trailer acted as a support for the truck. I don't think the brakes could be effective on that steep of a slope. It's amazing that the truck didn't slide sideways.
Nailed it
@@dmunro9076 brakes could have held, but the tires not skidding down that steep of a slope is certainly not very feasible.
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.
Fully agree.
But if any water did get into the wood in the metal tube, where would it go? Innovative buildings are all very well, but the more innovative and the more the design ignores norms like keeping wood in compression not tension, the more careful designers need to be to be sure they really have got it right. They built an 'innovative' building in my town back in the 60s. Biggest open span roof, slim pillars, etc. Lots of swank about it, lots of publicity. All the locals said, just look at it, that will fall down. That's a natural reaction, as people are conservative about construction, and they might well have been wrong.....but....you can see where this is going, can't you? 😉
I remember seeing wooden beams wrapped with forged steel straps. It seems the technique has been forgotten though.
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.
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.
And he would be wrong... wood is a bitch to cut across the grain... turn that wood on end and it splits with ease. The -only- way this method -might- work is if the "glulam" were forced into sockets which would keep the grain from having the ability to expand and split. EVERY bridge built like this WILL have a catastrophic failure as there is nothing to prevent the joints compromised by the fasteners from expanding and splitting down the grain.
@@76Chev4x4 The preliminary report on the failure, showed that several 2" +++ sized bolts where sheared off. The say the bolts appear to have failed due to stress. They also think, but do not know that it was the cause of the bridge collapse. Too early to tell, as some parts of the bridge has yet to be recovered.
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!
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
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 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.
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.
Then it's a good thing that they are not the leading civilian authority for the investigation of potential design failures. it's a good thing there are other concerned parties on top of that. if their design is at fault, it will be known. it's happening right now.
and materials suppliers, and construction contractors, blame the engineers. Yes, everyone tries to evade liability. The evidence is always there in the wreckage and "the truth will out" if you know how to look for it.
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.
fantastic thoughts- thanks...
Math is a good tool and sometimes the desire to use math or simulation causes people to oversimplify designs. Universities are heavily biased towards using too much math and too little craftsmanship and experience.
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.
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.
Just like the Romans with their Roman concrete. Everything was overbuilt, and only in compression. No tension allowed. Roman concrete lasts forever, but it's extremely useless in tension. Worse than wood. But they're weren't dumb, and many of their buildings are still standing, despite many wars, vandalism and earthquakes.
Farmers have been dealing with this issue for a long time - steel framed buildings with wood purlins etc and it's pretty much taken as read when you put that sort of shed up that the wood won't last the life of the steel frame. Should have added - I'm a farmer!
Most homes built in the US use wooden truss rafters that have wood under both tension and compression.
@@brnmcc01 No rebar, nothing to rust inside and break it. And some volcanic ingredients, some still standing fine a thousand years later even after world wars, trains and tanks passing over them.
Yes, the dreaded iron sickness.
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).
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'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.
Agreed. There a is box section to increase torsional rigidity and reduce flexing of the deck under side wind conditions. This has caused several dramatic, well-known bridge failures.
He knows that. He is just keeping it simple in order to focus on the main point.
I’m certain he’s well aware of that. However, his main audience is the average laymen, not an engineer, so he tends to explain things in simplistic terms.
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.
Where I worked in the US we called it the "pup."
on the east coast of Canada, we would call that a "twin steer truck with a pup trailer".
Interesting cultural context.
In Germany all Lories are LKW (load powered vehicle) but I am convinced that industry language to lengthen acronyms without animal references
@@453tye65e65e65e65 Same out west.
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.
Railroad bridges and trestles made of wood are rarely covered, and some have been standing for over 100 years in daily use. There are ways to make this work. (This bridge wasn't one of the ways.)
Um Almost all wooden bridges are uncovered.
@@lwilton They're still standing due to receiving repairs when needed.
politicians, I'm sure it met some "green" requirement.
Thanks for this one and greetings from Norway! The weakness of the joints seem obvious and not good at all. Keep in mind, though, that Norwegian media has reported that this bridge was used for transport weighing well over its certified capacity, which may have caused this.
I wondered about the load rating capacity of the structure. In the US every public structure must be load rated by a structural engineer within 30 days of going into service. This structure may have been fine for some time with lower weight vehicles, but I'd still be worried about rot at the connection points.
@@isaacm6312 AFAIK, we have similar rules in Europe, but then, I don't work with this, so I don't know wth details. The bridge just opened again, though and the first to drive across it, was the truck driver that got stuck on the bridge as it collapsed. He found it a bit scary at first, but said it helped.
“..He turned the front wheel- he or she- whoever was driving that..” 😂 he OR she? 🤣 👌 good one!
You have a real knack for explaining these things in detail and in just one take.
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.
I took a apart a deck made of treated lumber. Some of the post were perfect, and others had rotted away to almost nothing and they were all driven into the ground. There are differences in water exposure of the structure and how well the treatment process is done. The use of treated lumber in bridges designed for heavy trucks doesn't make sense, as the three bridge collapses clearly show.
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.
Politics. Wood is green. Steel is not. We got what we got!
At sixty years old i never dreamt someone could make materials science and engineering not only understandable, but fascinating! You are a gifted communicator and educator. Thank you Josh !:-)
🙏💜⚡️
There was a building collapse recently at the hotel across the street from where I used to work in York, Nebraska. The building was just 10 years old and the ceiling collapsed in the pool room, with one victim not surviving. There hasn't been any investigation into the reason for the collapse and it's just been swept under the rug. It would probably make a good video if there's any way to get it investigated.
That's shocking. Especially after a death. Wasn't there an inquest? In the UK our Health and Safety Executive would have been in there like a shot to investigate, just for starters.
There should have been a full investigation. There's a lot of corruption in these smaller towns and the contractors, inspectors, and investigative agencies often have a conflict of interest and will cover each other. I've seen pictures of the collapsed room and it looks like the decorative ceiling ledges were just nailed to the framework with no mechanical reinforcement. The nails simply pulled out of the wood and the entire 2x4 ceiling fell in. It's inexcusable
Yeah, definitely sounds like something shady going on.
I agree. I read about this and it bothered me tremendously that there was no investigation even though it killed an innocent kid playing in a hotel pool.
I saw a picture of the ceiling collapse online and it was bizarre to me that all of the sheets of drywall remained bound together when they fell from the ceiling. I would have expected them to break apart at the joint seams.
I was surprised the wood was laminated horizontal and not vertical it was always going to fail with the holes drilled in the direction of the lamination
This!
@@BuildingIntegrity Why? Don't the glues usual produce a joint stronger than the base wood?
I sow that rights at the begging
Laminated beams are made out of trees, which have grain. A vertical laminate would only utilize to the width of the tree, not the length, and would compromise the shear strength. Anyone who has split firewood or done woodworking would understand why these bridges are a bad idea.
@@andrewsnow7386 Stronger in tensile strength, not in shear.
Besides the bolt rusting issue which will occupy more space, there is the issue of thermal expansion. The steel will heat and cool and file a groove over time.
But there is a big issue, the speed of the truck. There is a wave moment that needs to be considered.
An example is loaded semi trucks driving on 4 feet of ice (in northern remote parts of Canada) have a speed limit. There is a wave in front of them as the coast along. If they exceed a certain speed the ice breaks up.
All drivers for that reason carry a large hammer to break the windshield because the door can't be opened to get out in an event ad such. TFS!
I am an Electrical Engineer but I did have some courses on this subject. As you spoke I was surprised at how much I remembered from 50 years ago. Thanks for making a true engineering analysis and not succumbing to the lowest common denominator.
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.
The marage steel alloy develops a thin layer of self-stabilizing rust.
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.
I am a bridge engineer and I applaud all the work you did here to get into a position to study the failure.
I suspect the truss diagonal that ends at node C would be in compression when the live load was approaching the support. I believe you have found the area where the failure initiated.
The problem here is certainly the joints. Everything about structural behavior of wood depends on the joints. Everything about truss behavior depends on the behavior at the joints. Your inside information on the research into wood doweled joint failures is certainly going to come into play when the final report is released.
I believe in steel connection design we have a similar mode of failure called "Block shear". Your observation that consideration needs to be taken for the glue laminations is on point. The gross section properties are only one part of this problem.
I am designing a wooden bridge right now for my Boy Scout camp. I don't think the other players understand how complex it is. They say they can get treated utility poles for the beams. But utility poles are tapered. I'm going to have to figure out how to secure the handrails to round, tapered utility poles. Yikes. They have conceeded that we will need to build a support pier somewhere along the length. They know they can't just lay them down on their sides and expect them to work.
I'm going to see if I can find some more information on this bridge.
Oh, and I agree, it seems optimistic to believe a treated gluelam bridge will last 100 years. Maybe a wooden bridge can do that in a very dry climate, but I wouldn't expect that in Scandinavia.
Thanks for the comment, and good luck on your bridge project... I too would not want to work with those poles as the main beams. A lot of strength there but the connections will be challenging. May consider cladding one side with PT boards bolted through the poles and then just build up from those sides.
@@BuildingIntegrity my coworker thought I should design the deck to be strong enough to carry the post load. I'll give it a look and see. The post is the key.
Very interesting analysis. The failure illustrates why axes and hammers use a split and wedge to fix the handle into a socket rather than dowels. With a wedge the properties of the grain facilitate and enhance the joint. Also shows why old composite trusses usually use iron for the tension members.
The wedge design used to hold an ax head in place is a good example of how to hold metal and wood together. The wood is compressed against the metal. The same could be done in this bridge design, if instead of using a large number of dowel rods, they were to use heavy metal plates on the sides with a smaller number of large bolts or threaded rods clamping the plates together and holding the wood and metal under compression. There should be no shear between the bolts and the wood.
How is differential expansion and contraction deal with.
2:27 - All of the diagonals are sloped in the same direction for the entire length of the bridge. Thus some of the diagonals and verticals were in compression, others were in tension, and some probably had reversing stress. As a continuous truss, it is indeterminate, depending on flex to even out the load across the 4 supports. This can result in concentrated stress at one point along the span. Looks like somebody had no clue about structural analysis. Also, a slender truss like this places much more stress on the members than a taller truss, it's a matter of leverage. Proper design might have allowed the bridge to last possibly 15 or even 16 years!
Very reminiscent of the clueless Florida International University footbridge collapse, which looked like a truss, but the seeming truss members were just decorative.
At least this bridge was across a shallow river, so the victims wouldn't drown.
Right now, the EU has many more pressing problems about greenness, such as freezing to death this winter.
Absolutely right. I suspect the architect wanted this layout and the inexperienced engineers said okay, no problems...
Norway is not in the EU.
@@ThermoMan But Norway is about to join NATO, and Russia has already stated it will no longer sell energy to hostile countries.
While not directly affected by the Nordstream 1 pipeline shutdown, one more wrong step and I bet they will be cut off too.
It's going to be a long, cold, deadly winter in Europe.
@@ThermoMan Norway suffers from the same green blindness as the EU.
@@derek20la There's so much nonsense in your comment it boggles the mind. Norway has been in NATO since its beginning, you're thinking of Sweden and Finland. Norway also doesn't import any natural gas, actually it's world's third largest exporter.
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'.
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!
Thanks Josh for another fascinating failure analysis video.
I was shocked to see an uncovered wooden bridge was being used to carry such heavy loads over water and with a huge span between supports! Wood, like concrete, doesn't perform well under tension. Also, wood has a much different temperature coefficient than steel, in addition to changing size with relative humidity. I see many problems with the steel/wood interface but, that would likely trigger a never ending debate. Anyway... I enjoyed the video, thanks Josh!
And what is the thermal expansion co-efficient of the glue, relative to the wood? And what about the wetting expansion/drying contraction, and freezing expansion/thawing-&-drying contraction, both of which would affect the wood, but not the glue? Lots of problems. At the very least, protect joints like this from getting wet.
@@grizzlygrizzle Yeah, the list goes on and on, that's why I didn't elaborate, as there are no end of opinions.
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!!
Looks like a bridge I'd make in Poly Bridge 2, praying as the heavy truck crosses it.
About the truck and trailer: with the load on it it weights at least 40 tons. As the bridge collapsed, from plane it should have been gone 45 degree uphill in a second. I assume the engine stalled immediately. If it had automatic gearbox, Automatic handbrake, it could not move even if the driver wanted to.
I believe the "tension perpendicular to the grain" language is referring to the wedge-like action you described earlier in the video -- a wedge pushes material apart in a direction perpendicular to its travel, and material being pushed apart can be described as tension. The second half of the next sentence is trying to give the material science of why wood is especially weak in tension along that axis.
What strikes me is how weathered and oxidized all the wood looks where it's pulled out of the failed joints. The sections of sound members show fresh clean material where they failed, but not at the joints.
Several years prior to the collapse of this brigde, there was done some analysis that concluded that just by its own weight the brigde was carrying 210% load. The analysis was sent to the correct autthorities, but they did not take action.
The laminate was also laid on its side - meaning the bridge was being supported by the wood in its weakest position. Anyone who's looked at the frame of a house could see you always put things like floor joists so they're on edge, because a 2x10 has much more strength going from edge to edge, than through the 2" thickness.
And glue laminated beams are no different. If you put them on their side, the bottom piece of wood used in making the beam is left to support itself, and thus is vulnerable to failure much more easily than if it was properly on edge, where all of the constituent pieces are equally supporting the load.
Who wouldn't have seen that during construction?
The first time I saw something like this bridge was an ultratruss. It was a 2" thick laminated web that was 18" high with 2x4 cords. It was to span a squash court. If you flopped them over they wouldn't carry a single person, as installed they were rated to over 4400lbs equally distributed.
The composite beam was on edge, thats the important part. I would argue the lamination was correctly oriented, but the connections were pretty obvious not. Glulam beams are typically stacked laminations like this, where lvl beams are layered they other way with much thinner veneers being vertical.
19:00 Perpendicular to the grain, tension pulls the crack open and compression squeezes it shut.
Though the wedge action is generated by pushing, the split opens ahead of the bolt so the grain is getting pulled apart (cross-links between fibers)
Ductile failure is where the hole-stretching (plastic embedding) is no longer able to accommodate the bolt's advance, and the piece begins to split -- the brittle failure.
Subbed! This was an EXCELLENT breakdown of currently known information on this unfortunate (and likely avoidable) incident.
I haven't seen it mentioned yet, but Hickory, North Carolina had a glulam pedestrian bridge that collapsed.. I don't think it was even a year old.
That was not glulam, it was timber frame. Still appears to have failed at the connection points.
You would think engineers would be super leery of joining highly dissimilar materials like wood and steel.
Bolts, pins.. point loads.. are just begging to have the dissimilarities cause a catastrophic failure.
@@christophertstone when was this? I live just an hour south of Hickory and don’t recall hearing about this.
A bit off subject, have you ever seen the “Mile High Bridge” on Grandfather Mt? It’s not wood, though I think some of the original was. It’s quite a bridge that has been reinforced to support the wind loads up there.
@@christophertstone I don't understand the difference. The arches were made of laminated timber, isn't that glulam?
@@shakeydavesr It wasn't actually a bridge that collapsed, but a set of decorative wooden arches over the City Walk pedestrian bridge between the Main Ave bridge and the railroad bridge over Hwy 127. It happened on February 18 of this year (2022). The 40 ton arches fell onto the pedestrian bridge and the Main Avenue bridge, but to my knowledge, didn't cause any significant damage to either bridge. IIRC the Main Avenue bridge was reopened shortly after the debris was removed. The arches were less than a year old when they fell.
@@Stephen-fb2zn Yes, the photos I'm looking at are laminated timber also glulam which is the same thing at least according to the Wikipedia page on it
IKEA bridge ?
Looks like it!
Only one piece was missing, you had a few extra of another piece, and it came with a little screwdriver to assemble it all
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.
I think you nailed it! there is a recently built wooden bridge near me, obviously much smaller scale than this one but there isn't a single piece of laminated wood on it, it's all solid timbers, massive ones, like I don't even wanna know where they got the trees this big to make this bridge from and how many of them they had to cut down. They also tripled them up, but at the ends they are bolted through with steel plates in a somewhat similar manner
I mean the great thing with wood bridges is that you can just regrow the trees. Using more trees than absolutely necessary isnt even much of a con.
When I went to school for engineering there was somthing beautifull and magical about how forces develop in a structure and that beauty was usually reflected in the design of the trusses or beams. The height of the truss does not reflect the load, they went against nature and physics to make an intentionally ugly bridge to serve some designers ego.
that long side just screamed when i saw it... WHY?!
oh yeah, ego
Yes, the slenderness of the truss would have been a big contributor in significantly increasing the tension force.
From 11:30 to 12:05 I heard/saw the bottom chords of the trusses at the new columns weren't supported by any steel underneath, just hanging by the pins. Am I understanding that correctly? If I am it's another poor design choice. What a disaster
Yes correct.
Also note, the prior bridge, had a cable acting as a lower truss, pushing up on the bridge. Adding a stabilizing member, above and below the traffic. The new design, put all the trust in the upper and lower truss alone. Not really having any failsafe time for anyone to catch a developing problem.
A great lesson of if it ain't broke don't fix it.
We have had very good wooden bridges and ships , dams , buildings etc that were far simpler, less costly, and lighter that have lasted for centuries. For thousands of years.
Here we have an example of ignoring the construction systems that were elegant and worked, and the stupidity of mixing widely dissimilar materials with different properties such as large thermal expansion coefficient and specific stiffness of steel with higher dimensional stability of timber.
And not allowing mechanisms such as plastic deforming repeatability of Stockholm tar calked bolted or dowelled joints that allow movement from moisture content changing, and dimensional changes without loss of strength and joint weakening.
And failure to appreciate that glues of similar elastic modulus to the timber are important to prevent glued joint failures.
There is a bamboo suspension bridge over a gorge in China built in 1100 AD that is still carrying lorry's across much larger spans than this, after a thousand years.
Built with nothing but split bamboo and seed oil based calking treatment and weaving systems.
How far our technology has regressed!
Ages of Wood and stone were far higher performance in every way than the age of weak short-lived metals and plastics like the rubbish alloys of iron and mutilated natural pitches in use here.
All for the sake of god's of profits and exponential breeding and hoarding of the rulers that measure value called dollars.
Sounds like we have a bunch of engineers that grew up playing video games and never tried to build anything in the real world. The software is only as good as the information entered into it and the experience level of the engineers doing the design work. Great video thoroughly enjoyed watching it.
Naw. Video game practice likely would have prevented this. This is hubris. "I don't need no stinkin' model!"
So basically they built this 100 year bridge out of steel, and... plywood... in Norway... where it's very wet, and has pretty good temperature swings... BRILLIANT! lol
Some of the RR Buildings and Matt Risinger videos from overseas european countries have shown how heavily laminated wood is being used overseas for home and apt building (some beutiful factories too). I wonder if this is a case of success in those areas leading to use of wood elsewhere that wasn't as suitable?
wonder if this type of connection would perform better if you put an outer brace on the wood as well, so it can't split open as easily.
What is most worrying is that the bridge failed under the load of a single truck whereas it will have been designed for standard pattern loads of vehicles at random positions over span. The reduction in load capacity compared to the design case seems to have been very significant.
You should look at the Video's for the rollercoasters, Son of Beast and El Toro, they had structural failures that caused main support bents and ledges that just split apart... Those incidents caused Track Sag which creates a pot hole effect. Both coasters had a severe enough structural failure that when the trains passed over that section it caused injuries to Riders.
Son of beast Failure occurred in 2006, the EL Toro incident happened in 2022.
Why a non symmetrical truss? And why the N shape didn't change direction at the centroid?
Is it just me or is the sound exceptionally soft on this video? I have my volume maxed out and can hardly hear.
Audio was OK for me. In my experience RUclips sometimes has temporary technical problems with really fresh videos, you might want to watch again.
@@blueboats7530 yeah, I’ve seen a few older comments about the sound being quiet, but it was fine for me so it might be fixed now.
Volume was very low. I cranked up both the computer speakers and YT slider, still barely heard it.
Yes, low for me too. That is, lower than most other YT videos. Though my hardware allowed me to crank up the volume so I could hear it easily.
15:28 How was the failure mode they found not obvious just from the orientation of wood fibers? All the wood to the the right of the leftmost holes are "in the shadow" of those leftmost holes, so far as tension is concerned -- that wood has little to nothing to pull on!
Having a failure mode isn't an issue; everything will fail if given enough force and the lab tests determined that amount of force, which the engineers then used to design the bridge. The problem is those lab tests were small scale, short term, and not exposed to weather or repeated cyclings. This connection method was never tested under real conditions.
@@rhamph "Having a failure mode isn't an issue; everything will fail if given enough force". Obviously. And sure, all the things you said are true, but don't relate to my point. On just the narrow point of the _particular_ failure mode being a surprise, as discussed at 15:28 -- I don't understand why it would surprise anyone given the fibrous structure of wood.
@@Graham_Wideman Yeah, it doesn't make sense. Sure, they put together numbers on the strength, but any experienced woodworker would laugh those numbers out of the building. Somehow no experienced woodworker was involved in any of these structures?!
100% agree with the comments regarding glulam and bad design of joints (pins between the glued layers, pins aligned in rectangular pattern etc.). Another thing which is kind of strange is the fact that ALL diagonal members are inclined in the same direction...I have run a quick FEM analysis of a truss (top and bottom chord + vertical and diagonal members) - and orientation of the diagonals in the same direction is far from optimal, increasing the magnitude of internal loads.
to help alleviate the splitting failure of wood connection, more confinement of splitting should be designed into the connection (box connection with double shear bolts, or cross bolting.)
As part of my civil engineering degree, I studied structural wood design and my 4th year project was a 2 lane, 100m, 4 span gluelam timber highway bridge so I do know a little something about designing gluelam timber bridges.
First, in structural wood design the connection points are always the weakest points. One of the biggest limitations of wood is designing connections to transfer load from one member to the next. At a quick look in this video without more detailed analysis I would tend to agree that it appears to be poor connection design that caused this failure.
Second, your implications that wood is outdated and the bridge should have been made of steel are total ignorance. Wood performs far better as a structural material than steel in many applications. Wood also has a far higher strength to weight ratio than steel. The only issue in using wood for structural members is knowing it’s unique properties and limitations. Just like designing with concrete requires more engineering details and calculations than designing with steel.
Wood is being used far more in structural design right now due to many factors but requires structural engineers to be skilled in wood design, more diligent, and, detailed in their designs and calculations, particularly connection points.
Steel has wonderful properties that don’t transfer well to wood. Joint design in steel is much easier than in wood. Glulams can make excellent bridges, but wood’s nature must be understood, respected, and designed for.
@@bradnail99 Exactly.
there's a reason the oldest wooden bridges are covered/roofed. rot
@@bradnail99 , "Steel has properties that don’t transfer well to wood", quite literally... while the investigation is still going on the couscous atm is that the steel parts changing more in size with temperature compare to the wood than have been calculated have been causing micro-fractures in the structure that have not been caught with the timed inspections.
(add inn that this is in some regions that have extreme temperature variations, all from 40*C to -50*C and not uncommon with 30*C difference between night and day)
@@element5377 Not an issue with properly treated wood. There are creosote treated railway ties that have been sitting on the ground for over a hundred years and they are just fine. We're not allowed to use creosote anymore but the modern (less toxic) treatments are almost as good.
1st.
Also there was a bridge collapse in Africa - during its public dedication ceremony.
Oh my... I hadn't heard about that one yet.
Thought that happened on Squornshellous Zeta😉
@@BuildingIntegrity the ribbon was structural. once they cut it, the thing went down.
Bunch of guys in suits standing there when it went down.
32:00 - I agree that there was much tension in the lower horizontal beams, which became maximum at the point load where the truck was, and the initial point of failure was most likely the AB lower horizontal beam separating from joint A. However, the AB cross member was normally under compression not tension. Starting at point C supported by the pillars - horizontal members cannot support vertical load. BC-cross compression vertical component of force is the only element holding joint B (top) up. Element B (vertical steel) tension holds B (bottom) up, which then supports AB-cross compression with vertical component of force supporting A (top). Likewise element A (vertical steel) tension supports A (bottom), which supports the next cross member to the left and so on. Because this pattern continues to the other end of the span (unusual; the direction of cross members usually reverses in the middle), this force is reversed at the other end, so that the vertical members are compression and the cross members tension, but again each cross member supporting the next vertical member. Once the strong tension of horizontal member AB failed, the bridge falling down lengthened the distance between the AB-cross ends, and it was ripped from the upper A joint. But AB-cross was usually compression, supporting the weight of the bridge to the left, and prevented from flipping over (upper end rotating down) by the tension of AB-lower and the compression of A-left upper. And as you said, the real cause of failure was deterioration of the wood in normal outdoor weather. There is a reason for "covered bridges" to be covered; the surrounding building struction maintained the beams and deck boards in a dry indoor environment so they lasted a lot longer.
I am from NSW in Australia and our roads people have been experimenting with different wood, metal concrete and composite materials all of them have movement sensors etc on them, the sensors have been cheap as chips for a wile so the expense would be monitoring
It's definitely funny to me to see the "let's make a wood bridge!" where they immediately end up at "which means we need to make the important parts in steel, and cover more bits of it in copper".
That, in and of itself is incredibly common, we’re always trying to utilize the cheapest material where we can get away with the cheapest material.
The pins should have been bolts which had large load-spreading plates and nuts to sandwich the assembly tight. Just driving pins doesn't do anything but create fracture points along the slots/plates. Truly shix design and never should have been subjected to huge trucks. This bridge "maybe" could be certified as a pedestrian bridge.
The problem with that idea is like my picnic table. After a decade out in the weather the bolts and screws are all loose, because when the wood expanded when it got wet, then shrank when it dried in the hot summer. Without someone coming along and checking every bolt for the correct torque several times a year, this wouldn't work. Add in the vibration of heavy goods vehicles and it gets much worse.
No pins, there should be steel sleeves wrapped around the wood beams. No holes in the wood, holes will always be a point of failure, when you drill a hole in wood it destroyes the integrity against any sheer forces. There would be claws in the steel sleeve to prevent sliding. On each side of the sleeve will be steel coloums connecting top to bottom. A large diameter steel cable on the diagonal connection.
@@zpgJiggleBilly Of course, after all that, the question is.... Why not simply build a steel bridge?!
I thought the same thing JP. Why not use the compressive force provided with through bolts, rather than just pins. Having said that, one of the tests Josh showed did use bolts, with apparently the same failure.
@@carlwilliams6977 I agree why not just build the whole thing of steel,l might add l have personally built gluelam bridges,but they were people bridges not for vehicles but they were almost this big
We/I miss hearing from you! Any updates on Millennium Towers? An error that huge in current times just mystifies me. Thank you for your excellent episodes.
This makes me think back to the failure of the Rosemont horizon event center in Rosemont Illinois outside of Chicago about 40 years ago or more,
They built the roof of the building out of wood and laminated wood members because the facility right near O'Hare airport and the theory was the Wood would control exterior sound entering the facility,
However it was constructed by steelworkers from Chicago and we're in steel construction skipping a few pins that don't line up is quite common and not generally detrimental to safety it is a safety issue with wood members. After the investigation and the discovery of the shorted pins the facility was rebuilt using the exact same plans and this time following them exactly, it is still standing to this day it has since been renamed the Allstate arena
It looks like an Ikea bridge designed by kids who snored through the class where the professor tried to teach them "The Map is Not the Territory".