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Re: Fixed or pinned support

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I think there is something else to keep in mind.  The real question is it
a "strength" or "displacement/service" issue?  As several others have
pointed out, a four bolt column base connection is never "truly"
fixed...that is it can always take some moment.  So if the issue is "I
need XX k-ft of moment to be transfered through the baseplate connection"
(i.e. a strength issue), then the specific detail may behave as a "fixed"
connection (i.e. the applied moment can be resisted by the detail, meaning
the connection [and building] will not "fail").  

If the issue is "I am analyzing this structure to determine the story
drift/lateral displacement" (i.e. displacement/service issue), then a 4
anchor bolt (opps...excuse me, anchor rods...Charlie, I keep forgetting)
connection may or may not behave as "fixed" since there will be SOME
rotation.  In this case, considering it pinned will likely be the
conservative route for determining the lateral drift while considering it
fixed would likely under estimate the lateral drift.

Scott


On Thu, 3 May 2001, C M IQBAL wrote:

> Hello Alex,
>    The support may only be considered fixed when permitted rotation is
> completely restrained. But in case of bolted joints some rotation always do
> occur which makes the base support to behave like a pinned joint.
>     Basically, in your case the column base supports are partially fixed.
> Most of  the computer programs do offer to model partial fixidity of
> connections. Such as  "Partial Moment Release" option stated after Member
> Release Specification, stating upto what %age the joint may be considered
> fixed. Such option is available in STAAD, I am sure other computer programs
> do have a similar option too.
>      Anyhow, considering the safety of the structure, when in doubt, it is
> safer to assume the joint to be pinned.
>    C. M. Iqbal
> 
> 
> ----- Original Message -----
> From: Nacionales Alex <acnacionales(--nospam--at)yahoo.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Thursday, May 03, 2001 7:52 AM
> Subject: Fixed or pinned support
> 
> 
> > 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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