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Re: Fixed or pinned support

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Alex,

	You haven't said how or why you are checking the structure.

	If you are using a computer it's easy to try both fixed and pinned
column bases.  This should give you upper and lower bounds on the
moments and shears throughout the structure and tell you whether you
need "some" fixity to make the structural system "work".

	If you do need "some" fixity I would consider the joint as a reinforced
concrete section with dimensions equal to the base plate (or a
reasonably adjusted approximation thereof) and reinforcing equal to the
anchor bolts to determine the moment capacity.  If necessary, you could
extend this procedure to determine a moment/rotation relationship (hence
a spring constant) but this sounds much too academic.

	Other writers have suggested that base plate stiffness and foundation
fixity may be questionable.  Both suggestions are valid and should be
considered seriously.


				Regards,

				H. Daryl Richardson

Nacionales Alex wrote:
> 
> Hello.
> 
> I am checking  a structural computation for a four
> storey steel framed building. The framing in the
> calculation shows fixed supports but the detail in the
> plan shows the supports are steel baseplates with 4
> 25mm-anchor bolts. The columns are directly welded to
> the baseplates. It is my opinion that this kind of
> connection is a pinned type connection and should be
> treated as such in the calcs.
> 
> Thank you for your comments.
> 
> Alex C. Nacionales, C.E.
> 
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