Disasters Archives - Mentored Engineer

Oh no! One of the premier coasters in the South is closed due to a structural crack! Luckily no one was hurt and the coaster closed without incident. Coasters are very safe so failures like these need to be investigated fully. I'm a firm believer of the saying, "you will learn more from one failure than a thousand successes." Lets see what we can learn from a video taken 100 ft away. Fury 325 is located at Carowinds, which is a unique park that straddles the North and South Carolina Boarder. This ride is one of three coasters in the park that crosses state lines which could provide a unique twist to the investigation that will ensue. The break occurred on the NC side. https://youtu.be/3B8XJ3O-H0w Video Transcript So it is with great sadness that I come to you tonight. Our beloved Fury 325 has suffered a severe structural inadequacy. Yes, the crack was discovered and Fury is hereby shut down, which sucks because it is one of my home parks. I've been on this many, many times. In fact, I got this picture right here with me and my two girls.Hey, I'm wearing the same shirt. First of all, disclaimer, I don't know the loads on this thing. I don't know exactly how it was engineered. So I'm going to replicate this as best I can. But please don't use this in a quarter law or anything.Disclaimer finished. OK, so let's mock this up in SolidWorks. We're going to run some FEA on it. So created a model. I did some FEA, which FEA is a two part process.One, we're going to break down our structure into a whole bunch of little lines. All these lines come together at nodes and lines themselves are called elements. Each element acts as a very stiff spring and we can measure how much that spring will deflect through the second part where we apply loads and restraints and then we see how all those springs work together and then we can add colors to those and find out exactly how high of a stress is in each point so the higher the stress the worse it is so you can see here that most of the structure is a dark blue or a light blue color but right around the welds we get to a very high stress now since the high stress is on the inside where that weld is and the rest of it's blueI can tell you that that crack started at that weld and worked itself all the way through that tube and fully separated it off now Corey wouldn't they be able to inspect this Yes, if you look at it though, it's a very unlikely spot to get inspected very regularly Okay, so they may have a guy walking on top of the rails But if you look down you're going to see the support and then below that is the weld So you're probably not going to readily see thatSo, they are required to have periodic inspections where somebody would need to get roughly within three feet of every weld on that machine and be able to inspect it. So, it was probably done in the off season and it's now six months later. Welds, when they start cracking, will go very slow at first and then they will go faster and faster and faster. So, we learned this with the Hernandez de Soto bridge where there was no crack and then all of a sudden there's like an 18 inch, 24 inch crack in the structure. All right.So why does a crack start in the first place? Well, there's two reasons for this. One, we have loads higher than expected. And the second one is we have an inadequate design with loads higher than expected. Probably isn't the case here.The train may be going slightly faster or slightly slower, varying the load. But generally speaking, we know how much. However, that may hold true with the two supports right next to it. So, if this one breaks, that load is going to get transferred now to the supports on either side, and that could be an issue. So, they're going to need to look at those supports as well, but they'll probably inspect everything.So that pretty much leaves us with the structure being inadequate. all right and I would agree with this one I don't like that tube to tube joint I don't like many tube to tube joints for the record as they come together you can see here when I take a section that there's very little holding the two tubes together it's a very thin section of weld that has very little penetration between the two Not a good design.So, what can we do? We can bevel the parts so that they fit together better, and we can fill in more of that area with welding. That avoids that little notch in there called a stress concentration. So, it allows us to have a much bigger area for that stress to flow through. So, the second thing we can do is add more weld to that just to make that throat of the weld, the thinnest part there, much bigger and take more load.So, the reason I don't like this weld is because it's a category D or E weld according to an ANSI specification. This is just like being in school. You got A through F. A is the best joints. F is the worst. So, we're at D and E. Not good.Needs improvement, right? So, it's difficult to change those. So, adding more bevel and more weld size to this is probably the best solution for that. The last thing I don't like about this joint is difficult to explain with tubing. So, let's switch it to plates.So, if I have a vertical plate taking an axial load and the other plate coming in at a 45 degree angle, those forces don't balance and we end up putting bending stresses into the vertical plate. that is not a good thing we need something to balance that force on the other side which this joint just does not provide so we're going to end up with high stresses no matter what all right so we want to avoid that joint as well so that's basically why this is happening we could probably dive a lot deeper into this but let's focus on the four things that need to improve going forward so the first thing we need to do is bevel that tube end so that we can get a lot more penetration get a better weld in there and then secondly increase the weld size a third option is to drop that plate where the track mounts to and all the way to that tubeand we can weld that together that that significantly drops the stress level finally we could add some other gussets in there too to make it work better so that's great future state but how do we get there well So for right now, the ride is shut down and I don't anticipate that changing anytime soon.So best case scenario, B&M will probably give them a rework solution where they take that component down, put it back together as best they can, and then probably add a whole bunch of plates around it and make it better temporarily. But the long term solution would be to get a new design, a new thing shipped from B&M, which can take several months. So right now, I think we're going to be down for the foreseeable future, probably into the off season, and then we'll see it open up probably in March or so of next year. So that sucks for me because I'm probably not going to go back to Carowinds if Fury's down.So, let's hope they get a solution very quickly. So, when you're done crying for your loss, please take a second to like, share and subscribe and follow The Mentored Engineer. Thank you for watching. Have a good night.

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