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How much track flex is normal?

J

jonnycat

Roller Poster
I was at my local park today, and walked by one of the rides to check it out. During operation I noticed a bit of flex in the track and supporting structures, which got me to wondering how much flex is normal during operation of a ride. I know there is always going to be *some*, but it looked to me like it was a bit much, what have you observed in your time at parks?

Video from today:
 
Dunno. Whenever I notice track or supports flexing under the weight of the trains, I actively try to ignore or 'un-notice' it, cos it's scary and it looks wrong and it makes me wonder about all kinds of things that you shouldn't wonder about when waiting for a roller coaster. Things like, 'what if metal fatigue caused that support to just
.. snap?'
So yeah. Nah.
 
Actually, track/support flex is a natural way to ensure that those things don't snap under the weight of the trains and riders. It's quite normal! If the supports stayed rigid all the time, glued to their respectively stiff, concrete footers, they would weaken over time and eventually break - since they wouldn't be able to transfer some of train's force into movement, instead absorbing all of it.
 
Depends on the ride type. Some rides are designed with a lot of give in certain spots while others do not. Supporting also plays a huge role as some sway (Intamin Impulse rides were notorious for that).
 
Newton's 3rd law: every action has an equal and opposite reaction. Literally everything moves when a load is applied to it, including roller coasters. Certain rides tend to flex more than others for various reasons, but let's remember that these engineers are good at what they do. They've analyzed every inch of track, accounting for load input, fatigue considerations, and factor of safety, and determined that the train load will not yield the track at all.

The good thing about using steel as a building material is that it exhibits what's known as a fatigue limit, which really isn't what it sounds like. Essentially, steel weakens as it's cyclically loaded based on a number of different factors until it reaches a certain point where it just doesn't get any weaker. At this point, the object can theoretically last forever but external factors, like rain and corrosion, tend to force situations like we saw with The Incredible Hulk.
 
jonnycat said:
I was at my local park today, and walked by one of the rides to check it out. During operation I noticed a bit of flex in the track and supporting structures, which got me to wondering how much flex is normal during operation of a ride. I know there is always going to be *some*, but it looked to me like it was a bit much, what have you observed in your time at parks?

Video from today:
Click to expand...
Spinball whizzer moves much more than this, and has done for as long as I can remember. It almost always attracts a comment or two from gp if you’re nosey and listen in like me. ?
 
Matt N said:
Didn't Son of Beast also sway @Snoo?
Click to expand...
Arguably it didn’t have enough flex, which is in part why it saw faster structure degradation. Without flex, supports and track bear more of the burden. Which leads to quicker wear.

A coaster I really enjoy watching flex on is Steel Vengeance. The biggest portion of work on this ride was reinforcing supports to cope with greater forces, and you will spot a good deal of track movement, especially during the second half.
 
Hyde said:
Arguably it didn’t have enough flex, which is in part why it saw faster structure degradation. Without flex, supports and track bear more of the burden. Which leads to quicker wear.

A coaster I really enjoy watching flex on is Steel Vengeance. The biggest portion of work on this ride was reinforcing supports to cope with greater forces, and you will spot a good deal of track movement, especially during the second half.
Click to expand...

Not quite. Less flex means that the joints or interfaces bear more burden. Bolts begin to shear and mounting holes begin to slot themselves and ultimately lead to entire components literally sliding under load. That's where you run into issues like on Son of Beast.

Displacement (track flex) is directly related to strain, which is directly related to stress, which is directly related to load. One could design a ride such that the displacement is reduced in a number of ways. One could simply reduce the load - lightweight the train or just run it without any riders. One could reduce the stress by making every support or bolt or track piece thicker. One could reduce the strain by using a stronger material. Engineers could design rides to have minimal flex, but track and supports would be massive and unnecessarily heavy, and the number of supports would increase significantly, leading to higher costs. Essentially, rides are designed to keep a good balance between being strong enough to withstand millions of cycles and utilizing a cost effective and assembly friendly amount of material to last millions of cycles.
 
Thanks to everyone who shared their experiences in this thread, I really appreciated them! I rode this coaster (Shock Wave at SFOT) today for the first time and had an absolute blast on it. Rode it twice today!

Of interest is that the tops and bottoms of the support beams narrow to what is some type of a joint, I'm guessing kind of like a ball joint, which allows the beams to have a range of motion both at the ground and at the track. On this track (a Schwarzkopf box track), they allow the track itself to move and sway quite noticeably. It's kind of unnerving when you don't know what is causing it, but Anton and his crew obviously knew what they were doing!
 
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