Bolt Clamp Load Loss Due to Cyclical Loading
Bolt Clamp Load Loss Due to Cyclical Loading
(OP)
Hello,
I am trying to determine why bolts are losing clamp load on a steel car port structure. My best guess is that a semi-constant low speed wind is causing cyclical loading in the bolts and structure. My problem now is that I need to run the calculations to determine if this is actually happening. Does anyone know of a standard or document that has calculations for how many load cycles a bolted joint can to go through before losing clamp load (how many cycles for a given external load)? Any help is greatly appreciated.
I am trying to determine why bolts are losing clamp load on a steel car port structure. My best guess is that a semi-constant low speed wind is causing cyclical loading in the bolts and structure. My problem now is that I need to run the calculations to determine if this is actually happening. Does anyone know of a standard or document that has calculations for how many load cycles a bolted joint can to go through before losing clamp load (how many cycles for a given external load)? Any help is greatly appreciated.
RE: Bolt Clamp Load Loss Due to Cyclical Loading
But you need to identify possible somethings to see if they are actually happening.
A properly designed joint will not lose preload because of cycling loads (within the design envelope).
RE: Bolt Clamp Load Loss Due to Cyclical Loading
a constant wind in unlikely ... more likely may be a buffet ? or a thermal cycle.
if some outside cause is making the joint relax, then you'd need to physically lock the head and the nut.
another day in paradise, or is paradise one day closer ?
RE: Bolt Clamp Load Loss Due to Cyclical Loading
Make sure that you are really getting this tight enough and then pin it.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Bolt Clamp Load Loss Due to Cyclical Loading
Ted
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
dvd-I haven't mentioned it yet, but I did not design the structure. The only info I have is from engineering drawings, images from Google, and second hand information from my manager. I have attached an image showing one example of the structure. There are different options for mounting the roof beam (cantilever/center mount)... Everything is galvanized steel, no countersinks, and the main members are made from boxed cee's welded together. The drawing shows multiple methods for tightening (torque nut, load indicating washer, and tension controlled bolt), but who knows what the contractor actually did.
Based on the feedback from everyone, I think my new solution is going to be to try and calculate the vortex shedding frequency first. If I have this I can maybe run a modal analysis (and maybe aeroelastic analysis) on the structure to see if there is some correlation. This will probably be the best way to show there is vibration in the structure and then I can just recommend locking hardware.
RE: Bolt Clamp Load Loss Due to Cyclical Loading
ok, that's not really a suggestion, as the previous physical restraints should work against vibration.
if you're saying your need Proof of vibration before doing a simple re-design, then place accelerometers on the roof near (and far) from the fasteners.
but i'd've thought that there's a reasonably straight line of logic from fasteners loosen > vibration loads > physical restraints
another day in paradise, or is paradise one day closer ?
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
If on hollow shapes and they will always work loose, your failure mechanizm is losing the nut and then the bolt - could you just paint the heck out of them?
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
Ted
RE: Bolt Clamp Load Loss Due to Cyclical Loading
"First, build it stock." (advice to budding hot rod engine builders before spending big bucks on all the speed parts)
RTFI (the stated take away lesson by one of my College freshman professors after administering one of those tests with written instructions on the first page to "read thru the entire test". Yes, the test questions were brutal. The last "question" was to NOT solve any of the problems but pretend you were working so your fellow students would not catch on.)
Please post detailed pictures of the actual "structure".
Please provide pictures showing the locations on the structure where the fasteners have "loosened."
Please provide nice detailed pictures of the counterfaces of the nuts and bolts that have "loosened." and the surfaces they were attempting to clamp.
Please provide some nice detailed picture of the counterfaces and faying surfaces of the structure's components that were clamped by fasteners that loosened.
As other mentioned coatings etc on the faying surfaces etc can embed and throw away any fastener preload that may have existed on day one.
A lack of triangulation could turn most any outdoor stRuKtuRe into a never sleeping always watching twisty turny version of the much loved (
After welding sh*t together one of my least favorite former bosses would often say "that's not going anywhere ".
A significant percentage of the time he was flat out wrong because his "designs" were simply flawed. I never pointed that out to him.
Ever since, if I hear any fabricator, tech or millwright say "that's not going anywhere " I can not help but stop breathing for several seconds and bite my lip.
Keeping a nut locked to its bolt will not necessarily prevent slipping and wear of everything in the deficient joint's grip length.
https://www.boltscience.com/images/boltf6.jpg
https://brushdestructor.com/wp-content/uploads/201...
RE: Bolt Clamp Load Loss Due to Cyclical Loading
looking at the structure it appears weak to start with. so the strength and rigidity will have a big factor on those loose hardware. it would work in a very low wind protected area.
would it be possible to revamp or at least rework it strengthen it. put in a windy spot and run the test.
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
RE: Bolt Clamp Load Loss Due to Cyclical Loading
A note on guessing - do NOT do it. I cannot stress this enough. Its unethical, makes you look EXTREMELY foolish, and ultimately reflects poorly on the rest of the profession. The customer's time and money is valuable, as is your own. If you dont use facts and standard process to draw logical conclusions then you open yourself and your employer to potential lawsuits if your guess is wrong, which it eventually will be. In many instances the best answer is the simplest and you said it yourself...
Until you rule out bolted joint design failure and joint assembly failures, any discussion of vortex shedding or advanced analysis is pointless bunk.
RE: Bolt Clamp Load Loss Due to Cyclical Loading