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 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.
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.
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.
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.
@@_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?
2 роки тому+9
@@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.
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.
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.
@@SockyNoob 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.
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.
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.
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.
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.
Thank goodness no-one was hurt. Also looks like they could have disconnected that truck from it's trailer and just lifted it out with a heavy crane and probably no damage either. Might have had to get the load out first though.
@@brnmcc01 They built a causeway out to the steel pillars, knocked down the bridge segment with the truck on it a bit, attached tow wires and pulled it off the bridge segment. Then they drove the truck away, still with wagon attached and the loads still on. If you search "NRK" and "brukollaps-pa-tretten" you can find a video of the operation. The video is 15 hours and the first 6 are the truck recovery.
@@zapfanzapfan Thanks for that. There are actually three similar videos, covering I think three days of bridge demolition and yes, also the recovery of the truck at around hour 6:00.
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.
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.
This UA-cam 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 love experts. I've been listening to "Practical Engineering" but it seems I'm going to add you. I saw your first report on the Davenport apartment building collapse. THANKS! Retired librarian
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 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.
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.
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.
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.
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.
@@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 !
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.
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.
This sounds like "poor man's" bridge building. Beans counters at the controls. No problem, and then again, a collapsed bridge is not their responsability, is it? At least these beans counters don't have to pay for a new bridge... So basicly everything that went wrong can (and must and shall) be blamed on these clumsy engineers. Sorry for being cynical, but I've seen these mechanisms happen too many times during my career as a civil engineer.
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.
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.
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 !!
I happened to be the guy how deals with the aftermath, some 1-30 years later. I 'am not surprised. I had cases where, engineers or project leads (for big 20+mio contracts),who failed completely to understand the water does actually flow downhill and yes, metal does actually corrode if you expose it to moisture.
The simple woodworker's knowledge cannot easily be turned into numerical values suitable for putting into a computer. Therefore it is often ignored by the sort of people to whom university education is more important than practical experience.
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.
3 very good observations. Collapse sequence, truck stiffness (I also estimated 2-4 feet of movement, based on the out-of lane alignment and steering angle), and cross rivets to force compression. I don't want to speculate about #4. It could have been the glue deteriorating in the weather; it could have been the glue acting as a water barrier keeping the wood from effectively drying out; natural defects in the wood; lacking understanding and design models. Something that I want to add. My parents had a swing in their back yard made from round wooden beams. And after only one decade those arm-thick pieces of lumber were split along the grain even without any significant loading, simply from the weather and repeated soaking and drying cycles.
I agree. With modern adhesives the strength of a glulam beam can be accurately modeled as if it were a single, seasoned timber. The idea of all those steel plates and pins buried in wood, which is hygroscopic, in an outdoor structure lacking a roof, tells me that even with the ability to endure the loads when built, these joints were doomed to fail over time due to corrosion.
add inn that while it is still under investigation it have shown that the bolts in the joints have been under-sized, this was notified in a report done on the bridge after first bridge failed but with bureaucracy having to go its rounds time goes on and then this one happen. if this have been the cause is still not verified and mostly wont be until next year with the speeds these type of investigations work at. but the wood it self have been written of as direct culprit and while the 14 large type bridges of same construction have all been closed down the several hundred smaller bridges made in same way are all open... but then there is a limit to how much stress pedestrians and light traffic can make on a bridge.
@@brrebrresen1367 Oh great, under-sized bolts when the main failure mode is that the bolts literally wedge their way through the wood. I can't see how that isn't the best place ever to save costs.
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?
@@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
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
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
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**
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
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.
Right, and we have many railroad bridges in the US that are over 100 years old, and carrying fully loaded coal cars which easily gross 100 tons or more. You can build bridges out of wood, but all the wood has to be supports and bracing. Building a bridge out of wood to make it look like a steel truss bridge was just stupid. Wood is not steel.
@@brnmcc01 On the northwest side of Chicago Illinois and there still stands a railroad bridge used daily supported by wood piers and bracing. It’s around 3300 North Kimball, just north of Kennedy Expressway.
Another useful bit of hardware for building wooden trestles is the "bridge washer" - a large diameter thick cast iron washer which spreads the compression from the bolt torque over a larger area of the wood, allowing for a higher torque on the construction bolts and tie-rods to keep the wood structure in place.
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.
Yeah, I noticed that too. I would have thought that they would have engineered the slots to coincide precisely with the glue layers. But as seen in the video, that still doesn't solve the problem of the dowels/bolts acting like round-edge wedges and splitting the grain. -- I also wondered whether any difference between the expansion co-efficients of the wood and the glue, exposed to extremes of temperature combined with repeated wetting and drying (with swelling and contracting of the wood, not the glue) may have complicated things further. Thermal expansion and contraction, freeze-expansion and thawing and drying contraction, and wetting-expansion and drying contraction, only the first of which affects the glue, and that likely differently from the wood, all together make for a bouillibaisse of weakening factors. And the cumulative effect over time? -- Those old New England COVERED wooden bridges seemed to have little problem surviving 100 years.
I am neither a skilled woodworker or engineer but logically to me what you say makes perfect sense. Especially the part where ONLY the pins are the primary holding force. I have built a few utilitarian things from wood which were screwed together AND glued and they remain solid after 15 years. I used well more glue than screws! But in this bridge could they have used glue? Will it adhere to the steel or could the steel be etched perhaps to enhance adherence? In the few places I have used anything even close to this construction, instead of pins I used threaded rod with double oversized washers on each end thus also keeping the wood in compression. Would that have been any better for these joints? Thinking also if some compression could have been added perpendicular to the pins thus limiting the ability of the wood to split? But all in it seems the ideas I note here would just be lipstick on a bad pig joint.
@@larrybolhuis1049 Wood glue is actually stronger than the wood itself. You can use epoxy or similar bonding agents in place of glue when you need to fuse wood and steel. Knife handle scales (the sides) are commonly epoxied in place. Etching the steel is also common practice, oftentimes with sandpaper to provide more surface area. There's a lot they could have done to improve the connections, but as you said, it's lipstick on a pig.
ב''ה, I think everything you wrote makes sense except in the last use of "perpendicular" you mean "parallel" as the pins/load pull and split through the gaps between the fibers? In the interest of saving lives, I'm going to have to watch this video a few times to see what they did get right and what's idiotic, or created by errors between plans and construction (any incorrectly oriented beams if the engineering plans got anything right). I think classical maritime construction has many examples of "strapping" the ends of beam type timbers or masts to prevent splitting and improve strength. Dipping the whole end of a wooden beam in e.g. a stronger than wood epoxy might be another method but create issues with interactions with the laminate glue unless the same chemical were used throughout, or create another interface for internal water buildup and swelling, rot, etc where the sealed portion ends. Connector techniques that can bear these loads gracefully will certainly be important to renewable construction; bridges are a good demonstration but in practical terms if you're using one for 100 years it's not a huge example of materials waste. USA does really need a solution to flat-land railroad grade crossings and returning to wood for 'drop on' timber bridges is the sort of thing I'd be interested in working on when it isn't shabbos.
@@ssvis2 Have heard the claim that the glue is stronger for years. Yet the glued joint seems most often the point of failure. Seems to me it's almost like interrupting the fibers results in a weaker joint. Hmm, who'da thunk? Sure, the glue may be stronger than the wood but it's not penetrating and completely interfacing with every fiber. Can see that more clearly with soft woods that have large growth rings. The glue doesn't adhere as well to the denser areas. Also the glue has to remain pliable. So on one surface some of the stronger fibers are mated with the weaker fibers on the other surface, and vice versa. Thus the joint is weaker than with continuous fibers.
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.
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...
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.
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.
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.
Charles Van Noland, Yes you're exactly right, they alternate the direction of wood in plywood for that reason. They don't in laminated beams like those. Wood likes to split especially at the ends.
I was thinking the same, but also realize that would reduce the tensile strength of the members at the joint in favor of improving the woods resistance to splitting, this could have been accommodated with widening the joint ends of the wood, but that would have only extended the life of the bridge a few more years at best, as the joint design is based on theory, and not even close to the tested models use to create the computer model. IE. the test used bolts with large washers to resist the splitting of the wood in at least one plane, but with pins there is no resistance to splitting in any plane.
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.
Correct. People have a simplistic and dumb understanding of wood construction today. They think all joints should be butt joints. Not even all metal hardware is all butt joints. I have a chest of metal drawers that has the equivalent of lapping. It has metal from the sides that wraps aroudn the front posts and is riveted in place. People should be forced to build projects in wood first which are then stress tested to make them understand principles. I was getting into japanese joinery because I thought "hey they know how to build with wood for stong connections". It was the first time I got exposed to that stuff so I thought they just did wood construction better but apaprently the west used to do it too. It just turned into lost technology probably due to cost cutting.
Not a dumb carpenter at all 😊 I’m studying up on cabinetmaking as I want to build a desk, and can see that grain direction and weight distribution dictate the type of joint that you use. What’s also bizarre is anyone who owns a log splitter would also see the issue. The splitter works by driving a wedge of steel or cast iron into the end of the grain, causing it to split along the length of the log. The engineer not only used square steel pegs, but also seems to have based the design on roof trusses, which to my knowledge are designed for a static load? I get the desire to ‘go back to basics’ but it seems to be purely an aesthetic choice. Yes we had wooden bridges in the 1800’s, but we didn’t have articulated lorries and speed limits.
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.
dingo, yes you have seen wood split in may ways and just when you didn't want it to. Can you imagine how they were able to drill those holes accurately? How do you keep a drill from drifting in wood? Also, all those holes close together really weakens the wood in a way. There has to be a diminishing return on the number of bolts at some point.
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!
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.
@@andrewellicott654 Wood is a good material for construction and has be used for centuries, and there are buildings and bridges made of wood that lasted centuries.. It's just stupid to use it BAD. And those joints in tension are stupid.
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.
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.
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
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.
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.
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 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.
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.
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.
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.
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.
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
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
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.
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.
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.
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...
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,
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 “
It'd be kind of like building a steel beam bridge on mars like its an earth bridge. The thing will get extrmely brittle at the lowest lows, and stay brittle until it warms up, and then people moving across will dynamically load it and snap! this wood will get wet and stay wet and lose its rigidity. Theres also the issue of expansion coefficient difference sbetwens all the materials. These people need to stick to legos.
Until they get wet and stay wet.......on a planet that is 71% covered with water......being used structurally to cross a literal body of water......I believe that just make glue lam a dogshit building material.
@@BrainScramblies I saw a short documentary on that a while back and it was surprising how obvious the flaw was, and I’m not an engineer. ‘It’s the same weight being supported on the vertical rod, we just cut the rod in two’ …but it’s now the weight of TWO walkways on that one connection instead of just one? And when that connection fails, both fall rather than just the one?
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?
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.)
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!
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).
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.
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.
@@grizzlygrizzle I can see the appeal, especially if weight is a factor and they design it so the ends are resting on something. You know, like how most wooden structures are built. It did not fail until after the truss failed. I would not expect it to last 100 years, but pros and cons.
@@markonw6661 Not arguing with you. Civil is not my background. I am advocating for doing those tests. Especially since it might do things like allow for a 25-50 year life deck that is light enough to meet othet design requirements. Of course, I also wish new vehicles were required to be tested for wear and rust. With the results on the window sticker...
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.
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.
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
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.
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!
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.
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..
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
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.
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.
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!
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
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.
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!
@@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.
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.
If they wanted to use natural materials, they could have just build a stone bridge. Correctly designed, those things last forever, even under heavy usage. An example of this would be the viaducts of the Semmering mountain railway. Construction started in 1848 (yes, 150+ years ago), it was the first proper mountain railway. The original stone viaducts are still in use and hold up to modern railway traffic.
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 .....
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.
@@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.
@@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.
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.
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.
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!!
We are heading into an age of technological, scientific and medical Lysenkoism. Were you to point out that an "ecological" design was faulty in some way, you would be denounced, likely as a "denier" or not a true believer in the "consensus". People who have been educated in systems where reality is a distant and unimportant detail are now starting to take over positions of responsibility. They will, inevitably find that though they will be able to ignore reality for some time, they will not be able to ignore the consequences of ignoring reality. A broken bridge or two may be the least of our worries, if they keep going the way they are and decimate the ability of the most productive farmers around the world from producing food, then you'll have a problem to worry about. Remember, in any productive endeavor, half of the productivity is generated by the square root of the participants (Pareto distribution). If they knock out even a small percentage of the most productive farmers, it will have a dramatic impact on food production. This is happening now, all over the world, not just in the Netherlands, but also in Canada, Australia, New Zealand, etc. The world is currently in the hands of some very unserious people, which is about the most generous assessment that you could make of them. It may take a miracle for us to get out of this without enduring a calamity that will be recalled for ages to come (assuming we will still be writing down tales).
New age politics have replaced religion for many, it takes some getting used to to identify but the truth is that ideological infiltration is nothing new, although its funny seeing it come from the very people that used to decry this very thing in science when it was coming from the church
@@Gumbatron01 Im sorry, but thats just ridiculous. There is truth in that our current lifestyle isnt sustainable, and that we have to make big changes. Im sure theres gonna be stupid ideas and ideological drive, but what human endeavour was ever free of that? Its harder to do something new, than to defend the status quo. And food production is quite literally the most secure and protected industry in the world. We have massive overproduction. Even in the poorer parts of the world, famine only exists where there is not enough logistics to distribute food. And even that lack of logistics is basically always caused by war and conflict. I dont get that doom saying. Look how fucking stupid people were a 100 years ago and earlier? Compared to that, we're a lot more educated and informed. The modern world can be frustrating, but its better than the past. And again, theres no real famine anymore.
@@termitreter6545 He's totally correct though. What we are seeing is very similar to the starvation that happens after communist revolutions, where ideologically driven technocrats end up devastating food production with top-down interventions. Starvation will follow. The UN has already predicted that an additional 300 million have been put into a situation of "food insecurity" with pandemic lockdown policies, and the EU is already discussing further "climate lockdowns". It's pretty nightmarish, as far as I'm concerned.
@@inthefade Thats not at all how reality looks though. "Food insecurity" isnt actually about food supply in western countries, its about money. The insecurity is not having enough money to live. But people in western countries dont starve or freeze, they can get free food if theyre in socially bad situations. Pretty much nobody in the world is starving because there is not enough food. The only thing that causes starvation in any scale is having a litteral war at your doorstep. And not even Ukraine is starving currently. So no, anyone claiming were running out of food, let alone because of food insecurity, has no clue what hes talking about. We have a problem of food waste, if anything, we got too much food to eat. Also, that lack of money for food is caused by inequality, which is powered by unregulated capitalism, where the poor lose and the rich win. So its a bit bizarre to pretend this has anything to do with fucking communism. No place in the world is doing anything "communist" right about now, not even china. Theres also no "climate lockdown" planned in the EU, whatever thats supposed to mean. In fact, climate is taking a backseat currently because of the economic and energy crisis. Energy is more dirty and subsidized than ever. Which shows what everybody should know at this point: The climate is always a low priority. Idk where youre coming from, but youve been listening to the wrong people if thats what youre afraid off.
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.
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
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.
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.
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.
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 !:-) 🙏💜⚡️
Another fantastic video Josh. We expect no less and you never disappoint. Question. All of those diagonal glue-lam beams going in the same direction, is that a design flaw that has no opposing directional strength? It caught my attention immediately upon starting your video. 👍👍👍
It all makes since because it's the same way we split logs. A wedge that travels through the grain. They are just installing the wedge inside the log and then splitting it with force applied on the log rather than the wedge(bolt). It's a log splitter.
According to preliminary accident reports (from SINTEF, a impartial 3.rd party) released a few hours ago, shows that the bolts has snapped due to overloading. Not the wood. The glulam is impregnated with creosote to reduce the effect of humidity. There are bridges that have heavier traffic, and have stood longer, that is made with gluelam. All the way back to 2005, where the highway passes over, and is still standing. The problem with the first bridge that fell, the contractors that installed it, didnt follow the specifications on the dowels as the designers required. This bridge seems like they didnt use enough bolts for the joints, or strong enough bolts. Cost saving measures when installing might be the major reason. The horisontal cracks that you are refering to, came after when the bolts snapped, and there became more load an the other parts of the bridge.
Thanks for contributing. I felt like in this video he prematurely started giving his opinion rather than reading an investigation report and translating that for the audience.
@@dimvoly even the locals do the same. Yes the accident could have been prevented, but shaming wood, when the wood held up, is not correct, as stated above, Norway has been using gluelam since 1958, and the first gluelam bridge was put up in 2005. And there are 38 bridges in total.
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.
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.
@@goawakeneveryone4365 Larry the lorry! ,a big strong truck who loved delivering things to help people, always with a big smile on his face as he got the job done, that was until he realized his engine was now old and smokey, fortunately Mike and Michelle his mechanics came to his rescue with a nice ecologically friendly electric motor and batteries so he could continue to help people, Larry is now sitting at the roadside as the first charger was busy and the second one was broken and now he has to wait for the lady with the truck with the diesel generator on to get him going again. For more Larry the lorry stories visit## .
My initial thought is you could greatly increase the strength of these type of joints by banding or completely encapsulating them in steel. For these failures the wood must expand when it splits. I believe keeping the joint in compression would greatly limit this type of failure
@@matthewholt2174 yep, this laminated notions confuses me. I see regular beams there, not laminated. Laminated is like plywood. So I assume that the lamination is used at the bed of the bridge, where can be seen layers of wood, but here are just regular plain beams.
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'.
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.
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.
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.
Eh, I think there's some survivor bias there. A LOT of bridges collapsed in the late 1800s. Sometimes trains unexpectedly dropped like an anvil through spans that should have held them. There was a lot of faulty design, a lot of bad maintenance, and a lot of failure to understand the properties of then-new materials like wrought iron.
@@SteamCrane Yup. Another factor was that trains rapidly increased in weight and power during that period and some earlier bridges simply weren't up to it.
Somebody explained it better. Anybody can build a bridge. But only an engineer can build a bridge that barely stands. People knew very well how to build stuff many centuries ago. Now for sure there is a lot more knowledge, but the budgets force engineers to leave narrow safety margins. And one mistake is enough to make the cards crumble.
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.
Are you talking about 32:30 into the video? The simple way to tell which truss-web members are in tension versus compression for something supported by two points is to identify the balance point of the bridge, and trace lines from there to the support point. The places where one's pen would be moving downward would be in compression; those where it would be moving upward are in tention. The only way I could see for the the AB chord to be in tension would be if the center of gravity of the portion of the bridge-plus-truck combination supported by the new steel pillars was to the right of point B, or the supports near the right edge of the bridge weren't doing much, and almost all of the weight was borne by the supports on the left.
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!!
I love learning about subjects outside my career. Forensic structural failure analysis is one of my favorites. Look into nuclear engineering...it's fascinating down to the level of mining the uranium. 52 here...
Wood is such an inappropriate material to use for the this application. What were they thinking? There is a reason they don’t make cannons out of wood.
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!
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.
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.
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'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.
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.
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.
@@SockyNoob 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.
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.
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.
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.
Thank goodness no-one was hurt. Also looks like they could have disconnected that truck from it's trailer and just lifted it out with a heavy crane and probably no damage either. Might have had to get the load out first though.
@@brnmcc01 They built a causeway out to the steel pillars, knocked down the bridge segment with the truck on it a bit, attached tow wires and pulled it off the bridge segment. Then they drove the truck away, still with wagon attached and the loads still on. If you search "NRK" and "brukollaps-pa-tretten" you can find a video of the operation. The video is 15 hours and the first 6 are the truck recovery.
@@zapfanzapfan Thanks for that. There are actually three similar videos, covering I think three days of bridge demolition and yes, also the recovery of the truck at around hour 6:00.
@@Delibro Yeah, there were more than one video. There was also one of just the 4 minutes of towing the truck off the bridge segment.
@@zapfanzapfan "I ain't got no time for that!" 🤣🤣🤣
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.
This UA-cam 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!
Thanks!
Another great video!!!
I'm just a fan of structural engineers who know they don't know it all and reach out to sites like this. Well done you.
I love experts. I've been listening to "Practical Engineering" but it seems I'm going to add you. I saw your first report on the Davenport apartment building collapse. THANKS!
Retired librarian
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.
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.
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.
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.
Has there been any indication that degradation of the wood contributed to the over-loading situation in the steel bolts?
Must be wood bolts, right?
This sounds like "poor man's" bridge building. Beans counters at the controls. No problem, and then again, a collapsed bridge is not their responsability, is it? At least these beans counters don't have to pay for a new bridge...
So basicly everything that went wrong can (and must and shall) be blamed on these clumsy engineers. Sorry for being cynical, but I've seen these mechanisms happen too many times during my career as a civil engineer.
@Richard Hack its not used to be cheap its used to be "green".
@@brandonreimer184 Well, a collapsed bridge can not be used at all, no matter what colour it was intended to have...😉
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.
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 !!
If you use wooden dowels sealed to the other wooden parts with a good glue, the joints won't come apart easily.
Why ? -- because engineers and architects NEVER ask a lowly carpenter if their ideas on paper will work in real life
@@Harry-zz2oh Not easily, but they can and will if subject to enough force. Source: my dining chairs.
I happened to be the guy how deals with the aftermath, some 1-30 years later. I 'am not surprised. I had cases where, engineers or project leads (for big 20+mio contracts),who failed completely to understand the water does actually flow downhill and yes, metal does actually corrode if you expose it to moisture.
The simple woodworker's knowledge cannot easily be turned into numerical values suitable for putting into a computer. Therefore it is often ignored by the sort of people to whom university education is more important than practical experience.
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.
3 very good observations. Collapse sequence, truck stiffness (I also estimated 2-4 feet of movement, based on the out-of lane alignment and steering angle), and cross rivets to force compression.
I don't want to speculate about #4. It could have been the glue deteriorating in the weather; it could have been the glue acting as a water barrier keeping the wood from effectively drying out; natural defects in the wood; lacking understanding and design models.
Something that I want to add. My parents had a swing in their back yard made from round wooden beams. And after only one decade those arm-thick pieces of lumber were split along the grain even without any significant loading, simply from the weather and repeated soaking and drying cycles.
Could hardening of the glue have contributed to brittle failure of the wood between glue surfaces?
I agree. With modern adhesives the strength of a glulam beam can be accurately modeled as if it were a single, seasoned timber.
The idea of all those steel plates and pins buried in wood, which is hygroscopic, in an outdoor structure lacking a roof, tells me that even with the ability to endure the loads when built, these joints were doomed to fail over time due to corrosion.
add inn that while it is still under investigation it have shown that the bolts in the joints have been under-sized, this was notified in a report done on the bridge after first bridge failed but with bureaucracy having to go its rounds time goes on and then this one happen.
if this have been the cause is still not verified and mostly wont be until next year with the speeds these type of investigations work at.
but the wood it self have been written of as direct culprit and while the 14 large type bridges of same construction have all been closed down the several hundred smaller bridges made in same way are all open... but then there is a limit to how much stress pedestrians and light traffic can make on a bridge.
@@brrebrresen1367 Oh great, under-sized bolts when the main failure mode is that the bolts literally wedge their way through the wood. I can't see how that isn't the best place ever to save costs.
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?
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
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
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
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.
I would love to learn more about how old school railroad trusses were built, do you recommend any sources, websites, or readings?
Right, and we have many railroad bridges in the US that are over 100 years old, and carrying fully loaded coal cars which easily gross 100 tons or more. You can build bridges out of wood, but all the wood has to be supports and bracing. Building a bridge out of wood to make it look like a steel truss bridge was just stupid. Wood is not steel.
@@brnmcc01 On the northwest side of Chicago Illinois and there still stands a railroad bridge used daily supported by wood piers and bracing. It’s around 3300 North Kimball, just north of Kennedy Expressway.
Another useful bit of hardware for building wooden trestles is the "bridge washer" - a large diameter thick cast iron washer which spreads the compression from the bolt torque over a larger area of the wood, allowing for a higher torque on the construction bolts and tie-rods to keep the wood structure in place.
@@raybod1775 Yup and I guarantee you a typical train is way heavier than that little gravel truck pulling a pup trailer :)
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.
Yeah, I noticed that too. I would have thought that they would have engineered the slots to coincide precisely with the glue layers. But as seen in the video, that still doesn't solve the problem of the dowels/bolts acting like round-edge wedges and splitting the grain.
-- I also wondered whether any difference between the expansion co-efficients of the wood and the glue, exposed to extremes of temperature combined with repeated wetting and drying (with swelling and contracting of the wood, not the glue) may have complicated things further. Thermal expansion and contraction, freeze-expansion and thawing and drying contraction, and wetting-expansion and drying contraction, only the first of which affects the glue, and that likely differently from the wood, all together make for a bouillibaisse of weakening factors. And the cumulative effect over time?
-- Those old New England COVERED wooden bridges seemed to have little problem surviving 100 years.
I am neither a skilled woodworker or engineer but logically to me what you say makes perfect sense. Especially the part where ONLY the pins are the primary holding force. I have built a few utilitarian things from wood which were screwed together AND glued and they remain solid after 15 years. I used well more glue than screws! But in this bridge could they have used glue? Will it adhere to the steel or could the steel be etched perhaps to enhance adherence? In the few places I have used anything even close to this construction, instead of pins I used threaded rod with double oversized washers on each end thus also keeping the wood in compression. Would that have been any better for these joints? Thinking also if some compression could have been added perpendicular to the pins thus limiting the ability of the wood to split? But all in it seems the ideas I note here would just be lipstick on a bad pig joint.
@@larrybolhuis1049 Wood glue is actually stronger than the wood itself. You can use epoxy or similar bonding agents in place of glue when you need to fuse wood and steel. Knife handle scales (the sides) are commonly epoxied in place. Etching the steel is also common practice, oftentimes with sandpaper to provide more surface area.
There's a lot they could have done to improve the connections, but as you said, it's lipstick on a pig.
ב''ה, I think everything you wrote makes sense except in the last use of "perpendicular" you mean "parallel" as the pins/load pull and split through the gaps between the fibers?
In the interest of saving lives, I'm going to have to watch this video a few times to see what they did get right and what's idiotic, or created by errors between plans and construction (any incorrectly oriented beams if the engineering plans got anything right). I think classical maritime construction has many examples of "strapping" the ends of beam type timbers or masts to prevent splitting and improve strength. Dipping the whole end of a wooden beam in e.g. a stronger than wood epoxy might be another method but create issues with interactions with the laminate glue unless the same chemical were used throughout, or create another interface for internal water buildup and swelling, rot, etc where the sealed portion ends.
Connector techniques that can bear these loads gracefully will certainly be important to renewable construction; bridges are a good demonstration but in practical terms if you're using one for 100 years it's not a huge example of materials waste.
USA does really need a solution to flat-land railroad grade crossings and returning to wood for 'drop on' timber bridges is the sort of thing I'd be interested in working on when it isn't shabbos.
@@ssvis2 Have heard the claim that the glue is stronger for years. Yet the glued joint seems most often the point of failure. Seems to me it's almost like interrupting the fibers results in a weaker joint. Hmm, who'da thunk?
Sure, the glue may be stronger than the wood but it's not penetrating and completely interfacing with every fiber. Can see that more clearly with soft woods that have large growth rings. The glue doesn't adhere as well to the denser areas. Also the glue has to remain pliable. So on one surface some of the stronger fibers are mated with the weaker fibers on the other surface, and vice versa. Thus the joint is weaker than with continuous fibers.
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!
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.
yea my thought is the wood goes in to a socket so it can't expand to split.
Charles Van Noland, Yes you're exactly right, they alternate the direction of wood in plywood for that reason. They don't in laminated beams like those. Wood likes to split especially at the ends.
I was thinking the same, but also realize that would reduce the tensile strength of the members at the joint in favor of improving the woods resistance to splitting, this could have been accommodated with widening the joint ends of the wood, but that would have only extended the life of the bridge a few more years at best, as the joint design is based on theory, and not even close to the tested models use to create the computer model. IE. the test used bolts with large washers to resist the splitting of the wood in at least one plane, but with pins there is no resistance to splitting in any plane.
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.
I was thinking about how if these engineers had shown this design to even a simple furniture maker, they could have caught these issues.
Absolutely. I cringed immediately when I saw what they had done. Any carpenter that understands basic engineering can see the issues here I believe 😅
Correct. People have a simplistic and dumb understanding of wood construction today. They think all joints should be butt joints. Not even all metal hardware is all butt joints. I have a chest of metal drawers that has the equivalent of lapping. It has metal from the sides that wraps aroudn the front posts and is riveted in place. People should be forced to build projects in wood first which are then stress tested to make them understand principles. I was getting into japanese joinery because I thought "hey they know how to build with wood for stong connections". It was the first time I got exposed to that stuff so I thought they just did wood construction better but apaprently the west used to do it too. It just turned into lost technology probably due to cost cutting.
Not a dumb carpenter at all 😊 I’m studying up on cabinetmaking as I want to build a desk, and can see that grain direction and weight distribution dictate the type of joint that you use.
What’s also bizarre is anyone who owns a log splitter would also see the issue. The splitter works by driving a wedge of steel or cast iron into the end of the grain, causing it to split along the length of the log.
The engineer not only used square steel pegs, but also seems to have based the design on roof trusses, which to my knowledge are designed for a static load?
I get the desire to ‘go back to basics’ but it seems to be purely an aesthetic choice. Yes we had wooden bridges in the 1800’s, but we didn’t have articulated lorries and speed limits.
Good point
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.
I'm sure flexibility was in the design but not seeing X braces between the columns is giving me red flags
dingo, yes you have seen wood split in may ways and just when you didn't want it to. Can you imagine how they were able to drill those holes accurately? How do you keep a drill from drifting in wood? Also, all those holes close together really weakens the wood in a way. There has to be a diminishing return on the number of bolts at some point.
I’m just a regular guy with some experience working with wood and even I saw that this was a bad design
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!
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.
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.
But Greta Thunberg said it would save the planet
They build a lot of high buildings now with CLT wood, but there have yet to be a fire in one of those - hope they calculated it all right...
@@ivankuzin8388 compression v tension. But I understand, a hot take should be taken regardless of facts
@@andrewellicott654 Wood is a good material for construction and has be used for centuries, and there are buildings and bridges made of wood that lasted centuries.. It's just stupid to use it BAD. And those joints in tension are stupid.
Glue lam? Omg those are for headers in residential homes, not for an exterior structure
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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,
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 “
It'd be kind of like building a steel beam bridge on mars like its an earth bridge. The thing will get extrmely brittle at the lowest lows, and stay brittle until it warms up, and then people moving across will dynamically load it and snap! this wood will get wet and stay wet and lose its rigidity. Theres also the issue of expansion coefficient difference sbetwens all the materials. These people need to stick to legos.
After reading your comment, I immediately thought of the Hyatt Regency walkway collapse
Until they get wet and stay wet.......on a planet that is 71% covered with water......being used structurally to cross a literal body of water......I believe that just make glue lam a dogshit building material.
@@BrainScramblies I saw a short documentary on that a while back and it was surprising how obvious the flaw was, and I’m not an engineer.
‘It’s the same weight being supported on the vertical rod, we just cut the rod in two’
…but it’s now the weight of TWO walkways on that one connection instead of just one? And when that connection fails, both fall rather than just the one?
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?
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.
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!
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).
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.
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.
And regarding the all-wood glulam deck support: "This is not a design I would recommend."
@@grizzlygrizzle Lol, but water + glue+ heavy goods vehicles is such a good combination though!! /s
@@grizzlygrizzle I can see the appeal, especially if weight is a factor and they design it so the ends are resting on something. You know, like how most wooden structures are built. It did not fail until after the truss failed. I would not expect it to last 100 years, but pros and cons.
Lol
@@markonw6661 Not arguing with you. Civil is not my background. I am advocating for doing those tests. Especially since it might do things like allow for a 25-50 year life deck that is light enough to meet othet design requirements.
Of course, I also wish new vehicles were required to be tested for wear and rust. With the results on the window sticker...
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.
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.
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!
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.
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..
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
Would a standard "construction orange" color work I wonder?
A reasonable request for a very common problem.
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.
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.
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!
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.
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.
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.
If they wanted to use natural materials, they could have just build a stone bridge. Correctly designed, those things last forever, even under heavy usage.
An example of this would be the viaducts of the Semmering mountain railway. Construction started in 1848 (yes, 150+ years ago), it was the first proper mountain railway. The original stone viaducts are still in use and hold up to modern railway traffic.
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 .....
You have a real knack for explaining these things in detail and in just one take.
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.
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.
Looks like a bridge I'd make in Poly Bridge 2, praying as the heavy truck crosses 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.
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!!
We are heading into an age of technological, scientific and medical Lysenkoism. Were you to point out that an "ecological" design was faulty in some way, you would be denounced, likely as a "denier" or not a true believer in the "consensus". People who have been educated in systems where reality is a distant and unimportant detail are now starting to take over positions of responsibility. They will, inevitably find that though they will be able to ignore reality for some time, they will not be able to ignore the consequences of ignoring reality. A broken bridge or two may be the least of our worries, if they keep going the way they are and decimate the ability of the most productive farmers around the world from producing food, then you'll have a problem to worry about. Remember, in any productive endeavor, half of the productivity is generated by the square root of the participants (Pareto distribution). If they knock out even a small percentage of the most productive farmers, it will have a dramatic impact on food production. This is happening now, all over the world, not just in the Netherlands, but also in Canada, Australia, New Zealand, etc.
The world is currently in the hands of some very unserious people, which is about the most generous assessment that you could make of them. It may take a miracle for us to get out of this without enduring a calamity that will be recalled for ages to come (assuming we will still be writing down tales).
New age politics have replaced religion for many, it takes some getting used to to identify but the truth is that ideological infiltration is nothing new, although its funny seeing it come from the very people that used to decry this very thing in science when it was coming from the church
@@Gumbatron01 Im sorry, but thats just ridiculous. There is truth in that our current lifestyle isnt sustainable, and that we have to make big changes. Im sure theres gonna be stupid ideas and ideological drive, but what human endeavour was ever free of that? Its harder to do something new, than to defend the status quo.
And food production is quite literally the most secure and protected industry in the world. We have massive overproduction. Even in the poorer parts of the world, famine only exists where there is not enough logistics to distribute food. And even that lack of logistics is basically always caused by war and conflict.
I dont get that doom saying. Look how fucking stupid people were a 100 years ago and earlier? Compared to that, we're a lot more educated and informed. The modern world can be frustrating, but its better than the past. And again, theres no real famine anymore.
@@termitreter6545 He's totally correct though. What we are seeing is very similar to the starvation that happens after communist revolutions, where ideologically driven technocrats end up devastating food production with top-down interventions. Starvation will follow. The UN has already predicted that an additional 300 million have been put into a situation of "food insecurity" with pandemic lockdown policies, and the EU is already discussing further "climate lockdowns".
It's pretty nightmarish, as far as I'm concerned.
@@inthefade Thats not at all how reality looks though.
"Food insecurity" isnt actually about food supply in western countries, its about money. The insecurity is not having enough money to live.
But people in western countries dont starve or freeze, they can get free food if theyre in socially bad situations.
Pretty much nobody in the world is starving because there is not enough food. The only thing that causes starvation in any scale is having a litteral war at your doorstep. And not even Ukraine is starving currently.
So no, anyone claiming were running out of food, let alone because of food insecurity, has no clue what hes talking about. We have a problem of food waste, if anything, we got too much food to eat.
Also, that lack of money for food is caused by inequality, which is powered by unregulated capitalism, where the poor lose and the rich win.
So its a bit bizarre to pretend this has anything to do with fucking communism. No place in the world is doing anything "communist" right about now, not even china.
Theres also no "climate lockdown" planned in the EU, whatever thats supposed to mean. In fact, climate is taking a backseat currently because of the economic and energy crisis. Energy is more dirty and subsidized than ever. Which shows what everybody should know at this point: The climate is always a low priority.
Idk where youre coming from, but youve been listening to the wrong people if thats what youre afraid off.
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.
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.
Bridge by Ikea.
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.
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.
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 !:-)
🙏💜⚡️
Another fantastic video Josh. We expect no less and you never disappoint. Question. All of those diagonal glue-lam beams going in the same direction, is that a design flaw that has no opposing directional strength? It caught my attention immediately upon starting your video. 👍👍👍
It all makes since because it's the same way we split logs. A wedge that travels through the grain. They are just installing the wedge inside the log and then splitting it with force applied on the log rather than the wedge(bolt). It's a log splitter.
According to preliminary accident reports (from SINTEF, a impartial 3.rd party) released a few hours ago, shows that the bolts has snapped due to overloading. Not the wood.
The glulam is impregnated with creosote to reduce the effect of humidity.
There are bridges that have heavier traffic, and have stood longer, that is made with gluelam. All the way back to 2005, where the highway passes over, and is still standing.
The problem with the first bridge that fell, the contractors that installed it, didnt follow the specifications on the dowels as the designers required.
This bridge seems like they didnt use enough bolts for the joints, or strong enough bolts.
Cost saving measures when installing might be the major reason.
The horisontal cracks that you are refering to, came after when the bolts snapped, and there became more load an the other parts of the bridge.
btw, Gluelam has been in use since 1959 in Norway, mostly in buildings and large industry halls, ports halls, hangars. etc.
Thanks for contributing. I felt like in this video he prematurely started giving his opinion rather than reading an investigation report and translating that for the audience.
@@dimvoly even the locals do the same. Yes the accident could have been prevented, but shaming wood, when the wood held up, is not correct, as stated above, Norway has been using gluelam since 1958, and the first gluelam bridge was put up in 2005. And there are 38 bridges in total.
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.
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.
Larry and the load 🤗
@@goawakeneveryone4365 Larry the lorry! ,a big strong truck who loved delivering things to help people, always with a big smile on his face as he got the job done, that was until he realized his engine was now old and smokey, fortunately Mike and Michelle his mechanics came to his rescue with a nice ecologically friendly electric motor and batteries so he could continue to help people, Larry is now sitting at the roadside as the first charger was busy and the second one was broken and now he has to wait for the lady with the truck with the diesel generator on to get him going again. For more Larry the lorry stories visit## .
My initial thought is you could greatly increase the strength of these type of joints by banding or completely encapsulating them in steel. For these failures the wood must expand when it splits. I believe keeping the joint in compression would greatly limit this type of failure
Agree. Also some kind of a dovetail connection would've been a common choice of any cabinet maker gluing together a drawer.
Or you could encase the vertically laminated wood with horizontally laminated wood or vice versa
@@matthewholt2174 yep, this laminated notions confuses me. I see regular beams there, not laminated. Laminated is like plywood.
So I assume that the lamination is used at the bed of the bridge, where can be seen layers of wood, but here are just regular plain beams.
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'.
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.
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.
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.
Is it just me or did we build stuff better when we didn't know how to build stuff?
In a lot of respects... yes.
Eh, I think there's some survivor bias there. A LOT of bridges collapsed in the late 1800s. Sometimes trains unexpectedly dropped like an anvil through spans that should have held them. There was a lot of faulty design, a lot of bad maintenance, and a lot of failure to understand the properties of then-new materials like wrought iron.
@@MrBirdnose Wrought iron being another material that should only be used in compression.
@@SteamCrane Yup. Another factor was that trains rapidly increased in weight and power during that period and some earlier bridges simply weren't up to it.
Somebody explained it better.
Anybody can build a bridge. But only an engineer can build a bridge that barely stands.
People knew very well how to build stuff many centuries ago.
Now for sure there is a lot more knowledge, but the budgets force engineers to leave narrow safety margins. And one mistake is enough to make the cards crumble.
"Tretten" not "tretton"
We don't do nearly as many silent letters in Norwegian as English does.
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.
Are you talking about 32:30 into the video? The simple way to tell which truss-web members are in tension versus compression for something supported by two points is to identify the balance point of the bridge, and trace lines from there to the support point. The places where one's pen would be moving downward would be in compression; those where it would be moving upward are in tention. The only way I could see for the the AB chord to be in tension would be if the center of gravity of the portion of the bridge-plus-truck combination supported by the new steel pillars was to the right of point B, or the supports near the right edge of the bridge weren't doing much, and almost all of the weight was borne by the supports on the left.
I think of the road bed as hanging from the upper bow, and the two are trying to separate. The upper bow is in compression, the deck is in tension.
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!!
masterclass presentation on so many levels, materials, corrosion, connections. Wish you had a donate button!
Yeah! Thank you for all the knowledge you teach us about.
I appreciate learning. Even at 63.
Peace my Friend
🌈🌎💞
You are so welcome. Thanks for watching!
@@BuildingIntegrity you are a good teacher. I have learned a great deal about buildings from the Engineering aspect.
🌈🌎💞
.
I love learning about subjects outside my career. Forensic structural failure analysis is one of my favorites. Look into nuclear engineering...it's fascinating down to the level of mining the uranium. 52 here...
@@coopdeville377 OH I do!
Quantum Physics, Quantum Mechanics, Metaphysics, medic/ Engineer for The Fire Service. So I hear you! Peace 🌎 💞
Wood is such an inappropriate material to use for the this application. What were they thinking? There is a reason they don’t make cannons out of wood.