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Old 29th April 2015, 03:15 PM   #1
Tony R
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Join Date: Apr 2015
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Default Flitch plates

Can the flitch plate thickness given by SB be shared across multiple plates?

Someone has designed a flitch beam and SB has given a plate thickness of 24mm. he proposesto use 2no 12mm plates. I am dubious that this is acceptable unless:

Either the plates are welded together, or
A third timber member is introduced to separate the two steel plates and thus prevent steel sliding against steel.

I know that this is not strictly a SB issue, but would appeciate others thoughts.
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Old 14th May 2015, 03:21 PM   #2
Tony R
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Default Re: Flitch plates

Nearly 100 views and no comments!

I cannot find anything on the WWW which supports the use of two steel plates back to back. Maybe welding is the only option?
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Old 9th June 2015, 01:28 PM   #3
Nigel Lewis
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Default Re: Flitch plates

Tony, I visit the forum from time to time and are also surprised how little activity there is generally across the whole forum. Either everyone that buys the software needs very little support, or maybe they are worried about showing their ignorance on what is a publicly accessible website. Naturally, if any of my clients should be reading this, I fall into the first category .

I can't claim to be able to throw any light onto the matter of two plates in a flitch beam, other than to ask another question, which depending on the answer might suggest that i fall into the latter category of user and not the former.

If the load is transferred from the timber members to the steel plate via the bolting arrangement, why would that be any different if the plate was actually two steel plates?
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Old 18th June 2015, 12:05 PM   #4
motorphotos
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Default Re: Flitch plates

Hi Nigel

Firstly I would question the design as a 24mm thick mild steel plate in my opinion is too thick and to have ended up with this size section the loads must be quite large ? so not only composite action between plate and timber should be considered but also the bolting to ensure load transference and also the bearings - pay particular attention to any point loads etc

If I have this situation I would use 3 timbers and sandwich the steel plates so the are not next to each other - plus I think you would need tooth plate connectors so that the bolt shanks are not bearing on the holes in the timber and to increase the circumference that transfers the load into the timber.

For the plate to be this thick I assume that the load must be masonry - its bad practice to carry masonry on timber and the NHBC have a specific clause that states this - they would not do this if it was not required and is to do with the timber shrinking among other things

just another comment - based on a 200 deep plate for example at 24mm thick the plate alone will weigh 37.72 kg/m run - it may be more economic to use a steel beam

just some thoughts hope it helps

regards

john
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Old 18th June 2015, 12:10 PM   #5
motorphotos
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Default Re: Flitch plates

Sorry Nigel meant to direct this to Tony R

Also on the welding issue the heat formed by continuous welding of the 2 plates together would buckle them unless its done in sections and alternated or in short sections say 50mm long at 300 centres say (don't know loads so cannot comment on weld length and centres ) but this could solve the problem of the plates buckling

This would increase the cost of fabrication as it would probably not be adequate just to tack weld the plates together

cheer

john
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