Richard,
I'm assuming that you are asking about shims at bolted shear connections. If so, a shim equal to or less than 1/4" thick may be used without reduction in bolted connection strength (See the green ASD Manual, @ Section J6). Anything over that is subject to reduced connection capacity and should be reviewed by the EOR. If you don't have access to the manual, I'd be happy to scan J6 and email it to you. It addresses both bolted and welded filler conditions.
Also, in the 2004 AWS D1.1, in Section 2, Design Of Welded Connections, refer to 2.10 Filler Plates, and look at 2.10.1 thru 2.10.3, and also look at Figures 2.1 and 2.9.
Thank you for the response.
This connection is welded rather than bolted.
I have a customer that stated that only one shim plate could be used in the connection, that is to say not stacked up (i.e 1/*" + 1/4" for a 3/8" shim). He stated that it is in AWS D1.5 or AASHTO. Though I do not remember ever reading this requirement, no one's memory is infallible. Hence, I posted the question to see if I missed something when I read those tomes.
Rich
AASHTO references D1.5 for welded filler plates.
In D1.5, look at 2.5 and Figs 2.1 and 2.2. I read those frowning upon the use of filler plates when joining tension and reversal of stress members except where allowed by design, and as prohibiting filler plates less than 1/4", if they will transfer stress. Also that filler plates 1/4" or thicker must extend past the joint enough to allow for a sufficient amount of weld.
And there is a bit more to it than I just described that would need to be considered.
So, in my opinion, the use of multiple filler plates is not automatically prohibited in every case, but your situation would not be acceptable because there is no way to use 2 plates without one of them being less than 1/4" thick. That is, unless the plates do not transfer stress.
Chet Guilford
To add to Chet's post, you'll need to size the shims long enough or wide enough to get enough weld to transmit the load required.
John Wright
I think the poster answered his own question, by noting his customer has told him (I assume in the contract) that only one shim plate could be used in this particular connection. If this is the case - then whatever it says in D1.1 or any other code is irrelevant. Only one shim plate is allowed.
As you might guess, my perspective is from the customer's view.
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