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RE: base plate software

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Ghassem,

The plates rolled in many years gone by warped and milling was a
requirement.  That went away somewhere in the '60's with better flatness and
quality right out of the mill.  The column ends had a problem when hot saws
were used.  The cold saws took over the market in the '70's and milling
requirements went away all together at the column base plate interface at
the steel fabricator's shop.

I use thick base plates on REALLY heavily loaded columns like boiler
buildings in power plants.  But the practice with these monsters is to ship
them out loose.  The columns have anchor bolt chairs with stiffeners below
(a bolt box as known by the veterans) to transfer vertical uplift load of
the brace and column to the anchor bolt.  The column is generally not welded
at all to the base plate.

I agree that for column to base plate interfaces that transfer moment, the
lamilar tearing should be a serious consideration.  When it does get to be a
concern, the bolt box will work to transfer the vertical column forces to
the anchor bolts even if you weld the base plate.  But the weld is
irrelevant.  The advantage is that your tension forces are transferred to
the anchor bolt using the stiffeners in shear as opposed to tension through
the base plate.

As noted by Rick Drake, the mode of failure must be considered in high
seismic design. 

Regards,
Harold Sprague


> -----Original Message-----
> From:	Khosrownia, Ghassem SPK [SMTP:GKhosrownia(--nospam--at)spk.usace.army.mil]
> Sent:	Thursday, June 15, 2000 2:02 PM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	RE: base plate software
> 
> Harold,
> 
> I had been told that thick plates are not always straight and their
> interface with the column end may not be perfectly continuous. I think
> this
> is the reason for possible milling requirement. The main reason I would
> stay
> away from them, if I could, is the lamination problems and pre-heating
> requirements. I just don't believe that, with exception to few situations,
> that we should be limited to using too thick of a plate to have to deal
> with
> all of this.
> 
> Ghassem.
> 
> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> Sent: Thursday, June 15, 2000 10:09 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: base plate software
> 
> 
> Ghassem,
> 
> Re: Ghassem Khosrownia's response:
> Why do base plates need to be milled?  
> 
> Regarding Paul Ransom's response:
> Most base plates are drilled with a standard or core drill (low tech) or
> some of the new CNC equipment cuts holes with plasma arc.  The kerf on the
> new plasma arc cutters (a problem at one time) is minimal and is accounted
> for in the cutting operations.  Punches, although still widely used, are
> on
> the way out.  I have never seen a base plate hole punched or reamed.  I
> imagine that it can be done.  I just have not seen it.
> 
> For economics I would look at Thornton, "Designing for Cost Efficient
> Fabrication", Modern Steel Construction, February 1992.  From this you
> will
> find the "rule of thumb" one pair of fillet welded stiffeners is worth 200
> pounds of steel.
> 
> Regards,
> Harold Sprague
> 
> 
>