My office is encountering a situation on a project that is in the construction phase where a line of columns has been placed several inches off line. The building is structural steel framing. The resulting problem is that the beams framing into the girders supported by the columns are too short. The connections are shear connections using clip angles. A 2 1/4" shim would be needed between the clip angles of the beam and the web of the girder to make the connection. "The Specification for Structural Joints using ASTM A325 or A490 Bolts, June 23, 2000" says that shims greater than 1/4" need to be extended beyond the joint and secured with enough bolts to uniformly distribute the load or the joint needs to be slip-critical. What I'm wondering about is whether there is an upper limit to the thickness of the shim. I can't find a maximum thickness allowed. My intuition says that a 2 1/4" shim is a bit excessive and might be pushing it. Has anyone ever encountered something like this or know what the upper limits are? Any info or references are appreciated.
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Upper limit to filler or shim thickness in bolted steel connections
- Thread starter rmv603
- Start date
rmv,
The idea here is that one needs to compare a non-structural shim, with a structural shim. Non-structural shims are limited in their thickness based on bolt diameter and bolt/nut strength. The reason being that you are simply increasing the eccentricity of the joint when using a non-structural shim. If you were to make the shim structural, i.e. an integral part of one of the structures, then you would be reducing the eccentricity. However, even a thick structural shim will produce high eccentricity. Therefore, for the condition you have, a series of structural shims would be desireable. But as far as I can see, there is not limit if the shim is designed properly.
And just in case you didn't think about it, you could halve your gap by shimming both connections of the girders.
Hopefully this helps to answer your questions. If not, let me know and I can try and be more specific.
jetmaker
The idea here is that one needs to compare a non-structural shim, with a structural shim. Non-structural shims are limited in their thickness based on bolt diameter and bolt/nut strength. The reason being that you are simply increasing the eccentricity of the joint when using a non-structural shim. If you were to make the shim structural, i.e. an integral part of one of the structures, then you would be reducing the eccentricity. However, even a thick structural shim will produce high eccentricity. Therefore, for the condition you have, a series of structural shims would be desireable. But as far as I can see, there is not limit if the shim is designed properly.
And just in case you didn't think about it, you could halve your gap by shimming both connections of the girders.
Hopefully this helps to answer your questions. If not, let me know and I can try and be more specific.
jetmaker
rmv603,
The section that you are refering to is talking about shims required at splices. There is no upper limit on the shims and I have seen this done before.
You have a couple of options that I have seen used:
1) Weld the shim and use "bearing" bolt values for checking bolt shear.
2) Use slip critical bolts and no weld is required for the shim to the girder.
The slip critical bolts are probably the way to go if the you have enough shear capacity in them because of the whole welding of the shim scenario and then you could use a shim pack. If you have other beams framing into those beams, I doubt you'll want to "halve" the shims.
The section that you are refering to is talking about shims required at splices. There is no upper limit on the shims and I have seen this done before.
You have a couple of options that I have seen used:
1) Weld the shim and use "bearing" bolt values for checking bolt shear.
2) Use slip critical bolts and no weld is required for the shim to the girder.
The slip critical bolts are probably the way to go if the you have enough shear capacity in them because of the whole welding of the shim scenario and then you could use a shim pack. If you have other beams framing into those beams, I doubt you'll want to "halve" the shims.
I think it would be a good idea to recheck the design of your shimmed connection, based on basic forces analysis.
Take into account such factors as eccentric load on the web of the column causing out-of plane deflection, and additional tension in the clip-to-column bolts caused by parallelogram slip between the shim plates if not welded.
Take into account such factors as eccentric load on the web of the column causing out-of plane deflection, and additional tension in the clip-to-column bolts caused by parallelogram slip between the shim plates if not welded.
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