Plate washers for oversize/slotted holes

[bugbus]

I have a few questions about plate washers that AS4100/AS5100.6 require for oversize or slotted holes. I want to make sure I have this right.

Taking the case of an M20 bolt as an example, it is clear from the code that anything other than a standard 22 diameter hole would count as oversize or slotted and therefore would require a hardened or plate washer that covers the entire extent of the hole plus an overlap of half the hole diameter. It is not clearly stated but I presume the bolt needs to be considered in its extreme position in the hole, rather than central.

The below sketch is showing a 28 diameter oversize hole, which is the largest allowed for an M20 bolt - requiring a 58 diameter or 58x58 square washer:

So far that's not too bad, but for a long slotted hole (22x50 in this case is the largest allowed), the plate washers start getting very unwieldy (102 diameter or 102x102 square in this case):

My question is, are people actually specifying and installing such large plate washers? Is it allowed to instead consider the bolt in its central location or does it need to be assumed right at the edge? I'm sure I have come across previous designs using oversize or slotted holes where plate washers were not specified.

Just curious how this is handled by others?

Thanks in advance

 

[PersonalProfile]

In principle that is my interpretation - I check the fastener anywhere in the slot, and I specify special plate washers, despite that others generally do not. I did not check your dimensions, though are apparently relatively correct.
I have historically convinced myself to use "oval" special plate washers, to relatively mitigate some your observations.

Kulak's discussion, "Oversize and Slotted Holes", may be worth a review, despite that you may be aware etc:

https://www.boltcouncil.org/files/2ndEditionGuide.pdf

 

[human909]

Typically one would use square plate washers:

https://www.allfasteners.com.au/square-flat-washer-galvanised-metric

And there is a reason why they come in 100mm x 100mm. I wouldn't worry about that extra 2mm, if you are turn the washer 45degrees.

Is it allowed to instead consider the bolt in its central location or does it need to be assumed right at the edge? I'm sure I have come across previous designs using oversize or slotted holes where plate washers were not specified.

You need to consider it at the edge as you have done.

Yes this clause is routinely ignored, especially for oversized base plate holes where it might actually be problematic. For a simple shear connection I wouldn't stress about it.

 

[bugbus]

@PersonalProfile, thanks for that, I realised I had that guide saved previously so I'll give it another look

@human909, thanks for the response. Unfortunately the situation I'm dealing with has some steel connections that don't quite fit, and so the original holes need to be reamed out or turned into slotted holes. The 100x100 washers (which is what I need) simply won't fit the hole layout, and so I'm having to come up with a bit of a compromise, maybe using a smaller plate washer than the code strictly requires.

This article from Hobson seems to think that in a tensioned connection, the lack of oversize washers can cause issues with the bolt tensioning:

https://content.hobson.com.au/newsletter/hobupd_vol024.pdf

 

[Retrograde]

Have you considered using OrbiPlate?

Reid™ OrbiPlate™

reid.com.au

 

[bugbus]

@Retrograde, thanks I'll check it out

 

[human909]

A smaller square plate washer eg 75x75x6 or even 50x50x6 should be 'fine'. Outside the code but 'fine' . I say fine because you should check it either by inspection or but rigorous analysis. If the slots are in a hefty 25mm plate I'd likely call it good by inspection with a thick washer.

If they are in an 8mm plate under tension the you might have other issues.

 

[PersonalProfile]

AS 4100 Supp1 states that AS 4100 is according to the following paper:

https://www.researchgate.net/publication/267382537_BEHAvIOR_OF_BOLTED_JOINTS_WITH_OVERSIZE_OR_SLOTTED_HOLES

I evaluate the following as generally useful fastener reference, that is "a bit easier" to read compared to Kulak:

https://www.cisc-icca.ca/wp-content/uploads/2017/03/HighStrengthBolting.pdf

All three of the references that I provided state the justification for a special plate washer.


I propose that any engineer that specifics fasteners ought to read Kulak.