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struengineer (Civil/Environmental) (OP)
26 Feb 06 23:28
I am designing a concrete footing for a steel framing building. The footing cannot resist any moment. I therefore use a pin support. I could not find a pin connection detail from my textbooks or steel manual. The only detail I found is to use 4 bolts at each corner of base plate . Can this detail be used for a pin connection?

Please help.
DaveAtkins (Structural)
27 Feb 06 8:34
Yes, a four bolt detail can be assumed to be pinned.

DaveAtkins

rholder98 (Structural)
27 Feb 06 8:54
I believe OSHA still requires a minimum of four bolts for erection stability, anyway.  Usually, you can neglect the inherent fixity of the detail.  I typically assume it is pinned unless I purposely design it to be fixed.
Ussuri (Civil/Environmental)
27 Feb 06 9:47
A four bolt baseplate, while assumed to be pinned will take some moment.  If you mean your found has to take zero moment whatsoever, none, nada, zip, zilch, you might want to think outside 'the box'.

I have seen a number of architectural details for exposed joints, where they have used a true pin, a couple of plates with a large, specially designed pin element.  If it is that critical you could investigate it.  Otherwise stick with the standard four bolt arrangement.
aerohap (Structural)
27 Feb 06 15:23
Pinning a joint is just idealizing the connection.  Treating the connection as a pinned location will just transfer the loads and moments to another location.  In this case you make the column top take the moments rather than the column base.  This is a common case for the design of the moments frames I work on regularly, the footing connection drives the design of the remainder of the structure.
axle (Civil/Environmental)
2 Mar 06 5:29
On this subject, when does a baseplate detail become assumed to be fixed? Being from Australia, the standard base plate connections as specified by the Australian Institute of Steel Construction for pinned base frames consist of either a 1, 2 or 4 bolt baseplate. Is it a function of the number of bolts? I.e. if there are more than 4 bolts does the base of the frame then jave to be assumed to be fixed or can you assume the base of the frame to be pinned regardless of the base plate detail?
Ussuri (Civil/Environmental)
2 Mar 06 7:06
In the UK we used to use two bolted base plates for a pinned connection.  However, this no longer done because of the CDM regs requiring a safe erection process.  A two bolt base plate is not very stable on its own.

Im not sure how a one bolt base plate works?? This would introduce an eccentric load in the column.

I think the critical word in your post is 'assume'.  As designers we often make assumptions to make our life easier but dont actually reflect reality.  So if you asssume it to be pinned, its pinned regardless of what it actaully looks like.

The Steel Construction Institute do have method for taking ito account some fixity when designing pinned base portal frames.  They allow you to model the base plate using a dummy member which allows some rotation and then begins to take some moment.
axle (Civil/Environmental)
2 Mar 06 18:03
Ussuri,

In Australia, the Australian Institute of Steel Construction shows a one bolt base plates for parallel flange channels. I have also seen it used with small hollow sections. I dont think its use is highly recommended due to its instability during erection - a point you mention in your post. In Australia I have only seen this detail used when there is next to zero or zero uplift force on the column and the base plate detail is really only used to locate the base of the column.
apsix (Structural)
5 Mar 06 18:04
A fixed base can not be assumed.
The baseplate, holding down bolts and footing have to be designed to resist the moment, shear and axial load.
Unless the moments are only nominal, typical pinned base details will not be sufficient.
On the subject of safe erection as noted by Ussuri; in Victoria (Australia) the new Occupational Health & Safety Act 2004 which imposes an expressed duty on designers of buildings & structures to ensure that OHS risks are identified and controlled will come into effect in July. This may well lead to similar column base bolting requirements (as well as other requirements) as required in the UK.
111213 (Structural)
6 Mar 06 5:06
it has nothing to to with the number of bolts.

the column is not infinite small.

so when there is an pressure force and a base plate
there is an resisting moment at the base of the column....


aerohap (Structural)
5 Apr 06 13:00
Correct me if I am wrong.  It seems to me that if the remainder of a moment frame is designed around a pinned column base, then the only time the column base will actually see a moment is due to a deflection in the connection in the remainder of the moment frame.  My conclusion being that the rigidity of the structure isolates the forces to purely axial forces.
MSDw (Structural)
5 Apr 06 13:18
Along side with the connectivity of the column to the foundation, the overturning resistence of the footing plays a considerable rule in whether it is a pin end or a fixed end; suppose you welded the column to a built-in plate in the footing and the footing has no much of overturning resistence ( i.e.: it can tolerate some little rotation ), then the end condition in this case is never to be taken as a fixed end! ..The structure behaves as it is built not as it is assumed. if assumed it to be pin, whereas in reality the foundation was very BiG - or somewhat deeper than average (maybe due to some huge vertical loading ), then the assumption needs to be revised.
connect2 (Structural)
23 Apr 06 15:39
How thick is your base plate?

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