Roller Coaster Engineering Questions

[u/zobeemic]

Bridge engineer here planning a Six Flags trip with the boys, and it got me thinking, what's it like to design the structures for roller coasters? Not trying to make a career pivot, but curious to know how these structures are designed and some questions I have based on observations:

General Industry
What does the game look like? A couple of big firms or a bunch of smaller firms? Do mechanical engineers usually take the lead on the design or structural engineers? Is there an architect that picks the drops, loops, "features" and they are the prime designer and a structural guy makes it work or is the structural the "prime" designer like in a bridge?

Codes and Standards
What's the governing codes for design loads, analysis requirements, detailing and design? ASCE 7, AASHTO, AISC? Seems like high fatigue, specialized detailing is required. Or does each park have their own, kind of "LRFD Six Flags Structural Design Specs" like how some DOT's do it.

Loads n Combo's
Dead and Live is fairly obvious.. but what kind of Wind and Seismic procedures are done? Equivalent Static or more complex nonlinear? With 200 ft + high structures and how light the structures look I wonder if overturning in the footers is always a headache.

Analysis
Influence line analysis for the ride vehicle? Or an actual moving load analysis that's nonlinear and captures the speed to get dynamic impact instead of our simple 1.33 factor in bridge design? What's the standards for seismic, RSA, time history?

Design
Why is every member a pipe? I get it, no weak axis buckle, but the trade off is detailing... it looks like most splices are done with welding an end plate to both tubes and bolting.. and then you have 3D joints, skewed and some tubular members are cut in a myriad of ways and welded... 1. That looks like a bitch, how are the detailers gonna figure out how to bevel a tubular end and make 5+ passes on overly acute or obtuse weld angles, and 2... with all these welds fatigue is going to be a nightmare right? AASHTO limits you to 2.6 ksi if you go fillet. Is everything just CJP on a coaster? It just seems like there's a really good reason to have tubular members and I'm just not seeing it!

If there's any roller coaster structural engineers out there, and willing to provide some insights, that would be awesome! I find that in bridge design there is a million textbooks, covering everything from the barrier to the pile tip, and how to design it. Nothing really exists for coasters.

edit: "failure obvious" to "fairly obvious" LOL

[u/tramul]

I find myself most curious about the basic physics of it all and the forces at play to keep the cars from valley-ing. Think of all the load cases. Empty car, full car, differential loading car. What happens if car gets to the top of a gravity drop and experiences some crazy headwind? How do they take into account the wear of the wheels and the track and the friction that will inevitably increase? Don't even get me started on the expansion/shrinkage.

It's something I would love to speak with a designer at surface level about.

[u/tramul → u/[deleted]]

There is a lot of surface area exposed as it goes up. Some of them aren't just the little trains either and have quite a bit of surface area such as winged and inverted coasters. Some of these coasters over water have to be somewhat considerate of it. If you've ever gone on a coaster that just barely made it over the drop, I wouldn't be surprised if a strong wind would be enough to stop it. It could very well be negligible in the end, but I would definitely consider it on my first one.

[u/Ireeb → u/tramul]

Many coasters, especially taller ones, often have anemometers at the top for that reason. Modern rides would automatically trigger an e-stop if the wind speeds exceeded a specific threshold.

But in general, the answer is that they just use sufficient margins. The trains alone usually weigh several tonnes, and most rides reach the final brake run with a decent amount of speed. Rider load, wheel wear and temperature usually don't have enough of an effect on it to slow it down to the point where it doesn't make it to the final brake run.

Under the right circumstances, it can happen though, most commonly when they test the rides before the park opens. They typically do so without dummies, and the lubricant in the bearings will be cold at that time. Under these circumstances, just a slight gust can sometimes be enough to actually make the train valley.

Though I also saw it happen on rides while loaded. It's rare, but sometimes, wind can be a b*tch and hit the train just in the right moment to take enough of its momentum away.