Using Washers to Increase Thickness

[dik]

The supplied fasteners are A490 bolts used in slip critical connections. The bolts are too long and the contractor is intending to include washers to build up the 1" distance. Is there any technical reason for not permitting this?

Dik

 

[desertfox]

Hi dik

There are reasons to not use washers to make a spacer ie:-

1/ It effects the friction coefficient of the joint, which can
change the bolt preload on tightening.

2/Alters the stiffness of the joint.

I'll post with some lnks shortly

 

[connectegr]

I would recommend a plate wash over area of the connection instead of washers. A plate washer with standard holes should provide even clamping force and perform as expected with proper length bolts. I am not aware of any RCSC guide for using additional washers with incorrectly sized bolts. Care should be taken to assure proper pretension achieved.

I have seen conditions with 2 or 3 washers. But 6-7, 5/32 washers sounds excessive.

http://www.FerrellEngineering.com

 

[desertfox]

Here is a good article, it shows how preload can be lost during tightening when relative surfaces slip:-

http://www.wds.com.au/pdf/why_use_flanged_nut.pdf

 

[StructuralEd]

Boss used to say, "if you have time, do it right."
Of course it was a facetious comment being a structural engineering office.

 

[dhengr]

And, my boss used to say... “if you don’t have time to do it right the first time, how are you ever going to find the time to do it over, or to fix it in the field?”