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Structural Steel and split/spring washers

Structural Steel and split/spring washers

Structural Steel and split/spring washers

(OP)
I'm reviewing EN 1090 and all related specifications relating to bolting. I have come to the conclusion that split/spring washers are not permitted by the standard yet I frequently come across structural steel with these washers.

I'm wondering has anyone here come across this before or does anyone have experience in the area.

As far as I know, these washers will actually result in faster loosening under load.

RE: Structural Steel and split/spring washers

It can be a mix. Under conditions where the clamping force is insufficient to keep parts from shifting they are ineffective.

However, the ability to maintain tension is the ability to maintain initial strain, some of which can be relieved by the tiny high spots crushing and reducing the initial strain. For a given tension in the fastener, the greater the length of fastener and the greater the length of the intermediate parts, the greater the initial strain. Adding a washer increases the initial strain, decreasing the loss in tension due to that initial crushing.


I see this effect mainly where thin sheet metal is held with screws - there is so little material being stretched that te slightest crushing removes all the elastic stretch. Being split washers doesn't matter - being a thick spacer is what is helping.

Ideally one might use a block with a hole to increase the amount of elastic stretch, but people see successful joints with the split washers and think the tiny amount of force required to flatten them must be the magic source. It makes a bit of sense as that springiness is visible while the microscopic elongation of the threads is not.

RE: Structural Steel and split/spring washers

Be weary specifying lock washers of any type for weather exposed applications. Most types of locking washers allow moisture into the hole to corrode the fastener invisibly. High strength steels tend to be anodic to lower strength steel structures which exacerbates this effect.

RE: Structural Steel and split/spring washers

TugboatEng,

Cool! I never thought of that one.

--
JHG

RE: Structural Steel and split/spring washers

" ... people see successful joints with the split washers and think the tiny amount of force required to flatten them must be the magic source. "

Lockwasher back story. DIN and ISO have withdrawn the standards for at least 10 types of lockwashers as having no locking effect, or resistance to embedding or “settling.”
MIL Standards have long made similar claims.


https://springipedia.com/images/bw-1.JPG

I was a little heart broken when I Checked out the stack of belleville type washers in parallel necessary to provide the clamping preload force provided by even a nominally torqued Grade 5 bolt. An even taller stsck is needed to approach a grades 8 or SHCS . 3DDave's "A block with a hole to increase the amount of elastic stretch " might be a more compact, easier to assemble detail.

A few score years ago, when I was a still a recreational downhill skier, on the ride up the lift checking the details of the attachment of the ski lift tower to meemaw earth usually met my expectation of a long grip length being needed in a REAL structural joint.
https://thumbs.dreamstime.com/b/ski-lift-station-b...

In Google images Nowadays long spacers seem to be rare. My suspicion is now the very long anchor bolt's installation detail includes a sleeve of substantial length below the tower base flange. The sleeve keeps the concrete from bonding to the anchor and accidentally shortening its effective length, and also allows the anchor some useful lateral flexibility for installation alignment with low stress .

RE: Structural Steel and split/spring washers

The following may be of interest:

1. The body of evidence, based upon both experience and experimental results, is that they [spring washers] do not prevent loosening and can be shown to actually speed up the rate of loosening in many cases.
2. Refer graph.

Ex:

https://www.boltscience.com/pages/helicalspringwas...

RE: Structural Steel and split/spring washers

Yes, I had a 2 day course on designing bolted joints for automotive use and at no time did star washers or split washers get mentioned as a useful option. The only time I see them is on electrical connections, I suppose the split washer tangles up in the strands of wires a bit. Whether that stops the nut spinning off is another issue.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Structural Steel and split/spring washers

I have one of those 1980's GM military adaptations of a Chevy K30. Most of the militarisation in involved putting star washers under everything. It's part of the RFI/EMP hardening. The star washers cut through paint to complete the connection. It's not for locking.

This is an example of a possible misconception of the purpose of a "lock" washer.

RE: Structural Steel and split/spring washers

I was once advised that the reason split lock washers work at all is not the split, it's the trapezoidal cross-section of the washer. They are thicker on the ID than their OD. The split is not the value-add because it takes only a small fraction of the torque to flatten it, and at that point the joint is nowhere close to the point of resisting slip. When fully torqued, the elastic compression of the unequal cross-section is more spring-like than a plain flat washer.

I'm no expert on this, but I'm surprised it wasn't mentioned here. Is it an old wives tale?

RE: Structural Steel and split/spring washers

geesaman.d,

I have never seen an explanation of how helical spring lock washers actually fail. I used to work with a guy who claimed that you tighten the screw down just until the lock washer is flat. This means of course that the screw is not tight. Any rotating movement in your system will rotate the screw out, resulting in a failed joint. I wonder if the problem is nothing more than a stupid tightening technique.

--
JHG

RE: Structural Steel and split/spring washers

My company uses spring lock washers in some cases but we have limits on size and material. Naturally, we use a torque specification regardless of whether it's spring lock washered, double-nutted, or just a locking nut. If we have failures in those spring lock washers or the accompanying hardware, I haven't seen a failure to speak of in my 17 years here. (I expect that typing that is calling up the demons already)

RE: Structural Steel and split/spring washers

Catch the link... I like loctite red, myself...

https://www.boltscience.com/pages/helicalspringwas...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Structural Steel and split/spring washers

Re: the link, yeah that joint already failed the moment the clamped members slipped.

So while I agree the test has value, it's really just comparing how various configurations perform in an already-failing situation. It does not mean the lock washers do not add value, it only means they can be overcome and if the joint is slipping to loss of friction and/or preload, it won't save you.

For the really severe cases, I'm a fan of double-nutting, lock plates, or lock wire.

David

RE: Structural Steel and split/spring washers

Even double nutting has to be done right...

https://www.boltscience.com/pages/twonuts.htm

I like Loctite red... or peening the threads below... even snug tight or slip critical works with HS bolts... For electrical stuff... I like Belleville washers where there can be vibration or load cycling...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Structural Steel and split/spring washers

Quote (High strength steels tend to be anodic to lower strength steel structures which exacerbates this effect.)


...didn't know that, thanks Tug.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Structural Steel and split/spring washers

"For the really severe poorly designed cases, I'm a fan of double-nutting, lock plates, or lock wire."

There are always cases where proper torque and fastener design are not practically achievable. Tapered couplings and sleeves for example, proper torque would push the coupling too far so double nuts or lock washers are commonly used. Soft or thin materials such as aircraft skins are another example. Interference fit threads are often used.

RE: Structural Steel and split/spring washers

I have an old tech book from a bolt company that calls split lock washer "Obsolete and Dangerous."

RE: Structural Steel and split/spring washers

How old... I've been aware of the failings of split washers for nearly 40 years...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: Structural Steel and split/spring washers

Quote (geesaman.d)

it only means they can be overcome and if the joint is slipping to loss of friction and/or preload, it won't save you.

That is exactly what is telling you they are useless.

Joint loosening has been very thoroughly studied. When joints don't have relative movement between parts, they don't loosen. This is why the 'right' answer for maintaining fastener preload is always more preload when the parts can take it. Any solution other than higher preload, even the ones that are highly effective (loctite, lock wire, Nordlocks, etc) are really just a band-aid to be used when your parts can't take the amount of preload required for the fasteners to stay tight.

RE: Structural Steel and split/spring washers

dik; copy right is from 1999.

RE: Structural Steel and split/spring washers

Thanks, david...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

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