Shim Plates

[dik]

I have a bunch of end plate moment connections that may require shim plates to make up the length between a couple of masonry walls.

Is there a limitation about the number or the thickness of shim plates I can use. I was thinking about 1" thick plates for adjustment.

Thanks

Dik

 

[KootK]

I doubt it matters for flexure but you'll need some shear capability at the joint which may govern the shimming. If I recall correctly, you can get away with a fair bit and there's an equation for downgrading bolt shear capacity to account for the shims. I dont see 1" being an issue.

 

[Ron]

With that much shim thickness, make sure the shims are welded together. That helps negate the bending aspect of fasteners and also concentrates the shear component in a single location as it should be.

 

[dik]

Thanks... shear loads are quite small... splices at 1/3 points, just a matter of giving a little space to fit the beams between a couple of existing masonry walls... shear in the order of less than 10 K. Again thanks... I wasn't planning on field welding the shims together. Beams cannot be full length because of existing construction this is fitting into. Can use slip critical if necessary.

Dik

 

[KootK]

How many shims are you thinking per sice?

 

[dik]

Two at most...

Dik

 

[CANPRO]

dik, there is a provision in S16 for calculating the reduced shear capacity of bolts that are passing through unfastened shims. I don't think there is a limitation on the shim thickness as long as you account for the reduced shear capacity of the bolts. I don't have S16 in front of me right now to give you the reference.

I have been in your situation a few times - new beam being installed between existing walls, with splices required to get the beam in the room. I assume your intention is to splice the beam on the floor and then lift in place. In this scenario, unless you have some slots in your end connections, the beam needs to scrape up each wall as you lift it...and if the walls are out of plumb then you could bind up.

My process has been this - 1) get a good survey of the existing conditions 2) design beam splices without shims or adjustability 3) design each end connection with slots or some other beams of giving you 1/2"± of play - this gives you 1"± total on the span which should be enough to get your beam in place.

If you need adjustability in your end connections just to lift the beam from the floor to the ceiling, there is no point in also providing adjustability in your splices as well.

 

[dik]

I have about 8 light 16" beams framing between two masonry walls 35' apart, the total length equal to the least dimension and shim as required. I don't know that there will be any variation in length... experience indicates differing lengths is likely and the reason for including shims.

I can simplify it a bit by putting the splice at mid span, at maximum moment, but would prefer to offset this to 20' + 15'. Any thoughts on splicing at mid span? Splice is easily capable of accommodating design moment. Just a personal quirk.


Dik

 

[j19]

Section 5.1 of the 2014 RCSC gives guidance on what to do when you have shims less than or equal to 1/4" and shims > 1/4".

 

[CANPRO]

dik, the number and location of the splices is of no concern to me really. Fewer splices preferred if they're going to be essentially the same detail.

My concern is that you're going to adjust the beam length to its final length and then hoist it in place - which I think would be (or potentially be) very difficult. For this reason, I would prefer to have some sort of slotted connection each end of the beam so the connection material can be moved inwards at the ground level giving you clearance between the walls, once the beam is in place you can slide the connection material tight to the wall and make your final connection.

I understand that you're trying to streamline the fabrication by using the same beam sections and adjusting the shims to suit the variance. But I would prefer to have each beam detailed to suit the existing geometry - splice some where along the length for access and then provide adjustability in the end connections.

 

[dik]

Thanks Canpro... and thanks J19...

Dik