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RE: base plate software

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One instance where I have seen bi-axially loaded columns is in a large
auto plant.  These buildings typically have several expansion joints.  The
lateral system (primarily for wind in my area) is moment frames created by
truss to column connections and/or maybe (if you are lucky) braces.  The
moment frames will run in both directions and consist of most, if not all,
of the column lines (to keep column sizes somewhat reasonable).  The end
portions of the building can be exposed to windward, leeward and sidewall
pressures.  On an end section of the building, since the expasion joint
will be on one side, there exists a load case where sidewall pressure
existings only on ONE side...therefore it is unbalance and can induce a
bi-axial load case.

You can also encounter a situation where the seismic code requires one to
impose 100% in one direction and 30% in the other direction...at the same
time.  If there are moment frames that share columns (generally something
that would be avoided if possible), then those columns would be exposed to
bi-axial bend.

Scott Maxwell


On Thu, 15 Jun 2000, Khosrownia, Ghassem SPK wrote:

> Harold, thanks for the update. I would do exactly what you said. Ship loose,
> transfer the load indirectly through the bolts, etc. This bi directional
> bending moment is what really bothers me. Where do we have a situation like
> this that we can not avoid? Machinery support? Certainly not in buildings,
> do we?
> 
> Ghassem.
> 
> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> Sent: Thursday, June 15, 2000 1:55 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: base plate software
> 
> 
> 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
> > 
> > 
> > 
> 
> 
> 
>