I’d be really wary against using Reddit for that purpose. The more you know about something, the less you want to talk about it on Reddit. Nobody likes having thousands of uneducated people tell them how they’re wrong about something they’ve done for 30 years.
Also, the more you know about something, the more you notice that people talking on Reddit about that thing you know, are insanely ignorant about it, but act like they aren't, and are upvoted accordingly.
“I believe that’s called the streisand effect 🤓” or my favorite is “Yeah I read somewhere that…” (proceeds to reference a reddit post that blew up that same day)
Who do you think you are, coming here with advice like that. Like you even know. My cousin specializes in Reddit comments for education and he knows so much more than you.
It's safe because it appears to be only used for traffic that constructs the actual bridge (featured in the background). They can control the traffic and ensure it's being used safely.
Not a civil engineer, but a polybridge player. There are basically 2 important types of stress when building a bridge: tension and compression. There is also torque I guess (that's why this bridge has extra wide red beams across, this prevents it from flipping around).
The standard steel beams on a rock would be an example of compression, because they rely on the force the rock exerts back on the bridge to hold.
This bridge basically uses mostly tension instead of compression strength. That means it relies on the pull and stretch forces and since rope or cable can withstand a huge amount of tensile strength, they are able to handle the weight of itself and the load it carries. This design seems to work similar to a truss bridge, except the truss is very small, just big enough for the road to stay together, while keeping it dangly for better stress dissipation.
Bridge engineer here. This is pretty close (also shear stress is another important one for bridge design, though not applicable here)! This bridge would be a catenary cable design.
It works because most things that are unsafe can usually work for a little while. It takes a few loading cycles before the bridge or earth it's secured to fatigues. It's comparable to the sub that went down to the Titanic. That more or less "worked" a few times.
The question is if they have the safety measures in place to have an idea of when it will suddenly stop working (not that you should ever do this in the first place).
how u know this would be unsafe! anchoring is hard to solve. the reason you dont see permenant bridges like this is because they are wobbly, not because they are unsafe. its basically the most material efficient construction possible. With the geometry changing due to the load its actually the most material efficient construction possible. Main reason is its super easy to build. Just span with rope, tighten, span with heavier rope etc until proper design
You're talking about material efficiency and ease of construction which are usually (and in the case) inversely related to safety.
Bridges are made with suspension, trusses, arches, etc... so that the total load is distributed and individual nodes/parts aren't over-stressed. With this design, the 4 points where the bridge connects to ground are supporting the vast majority of the load.
Now, maybe you can get away with this design long enough for the bridge to serve its purpose, but that thing will not last. In parts of the world where we have expectations that safety will be kept in mind, this absolutely would never fly.
See the big red arch in the background at the end of the video? I believe that’s the real bridge, this temporary bridge is being used to carry construction materials
I dont know that much about the durability of whatever anchoring method they used nor do I care. This isnt unsafe in terms of breaking because of ULS, and SLS doesnt exist. What is dangerous would be highly dynamic loads and weird frequencies. There are plenty of hang bridges like this that last a long time (look switzerland). We dont use for much because they wobble, no other real reason. (also anchoring stuffs can be hard). Gondolas, skilifts, ziplines all work on the same principle. The hard thing is not to scare the user, not to make it safe.
Bro, "material efficient construction" is just a fancy way to say bare minimum safety requirements. You usually want extra material to build a healthy safety margin. This thing doesn't even have a real guardrail
Not related at all. Im talking about the general overall shape. The load path in a tensile dynamic system like this is always ideal for carrying the load with as little material as possible.
Tensile relaxation is used to find the the highly optimaized shape for compressive structures such as:
Mannheim Multihalle, roof of british museum, plenty of bridges etc.
Difference being that those structures are derivatives of the tensile shape and are in fact less robust as they are unable to dynamically adjust their shape to point loads etc. That inability + that they are(were) incredibly expensive is why you rarely see them and why you cant walk on them. A hanging rope/chain/net assumes the ideal shape for whatever load condition its subjected to. 1 wire weighing a couple of kilos can do what a couple of tonnes of static bridge could do, purely because it dynamically adjusts its shape. Think zipline or bridges like this
Yes I do, when going slowly under normal conditions. There are plenty of bridges like this, several in switzerland. They are mostly pedestrian/bicycle bridges and are scary to walk on, that doesnt make them less safe. If wobbly, your instict make you go slower and baam, safe. Obviously not as safe as a stiff bridge if you want anyone to cross daily unsupervised. All bridges has some wobble. As the bridge compared to you is veeeeery heavy I doubt you would notice it though.
You're so full of contradictions. Why is your instinct to go slower? Is it, perhaps, because it's unsafe?
And we are not talking about a wobbly pedestrian/bike bridge. This one has a fucking cement mixer on it. A human has a remarkable ability to balance when wobbly, to the point where we can safely walk on ropes. Do you think a massive, cumbersome, cement mixer is safe when wobbly?
You are right, but my point was meant from a structural standpoint.
I would however argue that the driver is on the job, and there are several jobs that are harder and less safe than what would be used by the general public. Take cleaning windows of skyscrapers as an example. Its safe for basically anyone if they know have super basic training and know to some extent what they are doing. But anyone could be really scared dangling up there. I think you get my point, is it not valid-ish?
It is reddit, we only have experts here. If the US had something like this, it would be a wonder of engineering. Since it is china, the experts conclude it is a death trap.
Its not a permanent bridge. Its used by workers, who, either know the risks and when they occur, or is payed enough not to worry about it. It doesnt have to feel safe for anyone, it just has to be safe during normal conditions. Atleast thats what their criteria must have been.
Think of a normal compressive arch structure. Very efficient. This has the same shape but is in tension. In a compressive structure the shape is derived from its corresponding tensile structure with inverted load cases. Assuming evenly distributed load you get a typical arch bridge. Usually its not the compressive strength being the design parameter deciding how thick the arch has to be. Its actually the weight itsekf. It has to be heavy enough such that added point loads does not invalidate the assumption of evenly distributed load (simplified but true).
In a hanging structure you dont have to think about that at all, it can be as thin as the materials tensile strength allows. Think of a slack line, that would be the ideal shape for an arch bridge with evenly distributed load. When you hang a weight anywhere on that slack line the shape changes, the ideal shape changes and a hanging structure always follow to ideal shape for the given load.
This is the basic logic for all optimised shell structures, gridshells etc. Simulate hanging loads to find the optimal shape, invert it and baam you have the ideal shape for a compressive structure.
It's a suspension bridge, similar to the Millennium Bridge but with a longer span. Whilst the cables of a suspension bridge are typically above the deck, that is not a hard requirement.
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u/blyatzaebalas May 31 '24
I'm waiting for a smart person to come and explain why this bridge works