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Fw: Steel-Detail: Re: Erecting Steel Braced Frames with Bolted Connections

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> From: Jackie_Riggle <Jackie_Riggle(--nospam--at)email.msn.com>
> To: Fountain Conner <fconner(--nospam--at)pcola.gulf.net>
> Subject: Re: Steel-Detail: Re: Erecting Steel Braced Frames with Bolted
Connections
> Date: Friday, June 25, 1999 6:46 PM
> 
> Fountain,
> I've been detailing several years.  One of the problems with erection on
the
> project mentioned is the base plate elevations not being exact.  When
braces
> are bolted everything has to be exact.  With only 1/16" tolerance in the
> holes, if one base plate is up 1/8" and another one is down 1/8" you're
in
> tolerance, but the base plates are now 1/4" difference.
> Another thing is are the braces bolted to the bottom of the beam flange? 
If
> they are,  with mill tolerance, a beam depth can over run or under run
and
> if the shop doesn't hold the location of the hole from the brace work
point
> instead of the bottom beam flange, once again tolerance is greater than
the
> slop of the holes.  The holes being oversized only 1/16" of an inch means
> that the most adjustment you have at any end is only 1/32".
> I realize that in the olden days when rivets were used, in lieu bolts,
> things went together and stayed that way.  Find an oldtimer and ask how
much
> tolerance they had in the rivet holes.  Maybe craftsmanship in the shop
was
> better before machines did most of the punching?
> Just things to ponder.
> Jackie

> >> From: Garry Frederick <GFREDERICK(--nospam--at)HNTB.com>
> >> To: 'seaint(--nospam--at)seaint.org'
> >> Subject: Erecting Steel Braced Frames with Bolted Connections
> >> Date: Thursday, June 24, 1999 4:40 PM
> >>
> >>
> >> > What facilitates erecting steel braced frames with bearing bolted
> >> > connections when using standard holes whose diameters are 1/16-inch
> >> > greater than their matching bolts? Recently a 22-foot by 22-foot by
> >> > 100-foot high tower whose X-braces crossed at the mid-span of beams
at
> >> > alternating floors went up poorly because the holes in the braces
did
> >not
> >> > match the holes in the connecting plates on the columns and beams.
Even
> >> > after reaming some of the mismatched holes to accommodate the next
> >larger
> >> > diameter of bolts, more than 120 mismatched holes remained. What
> >finally
> >> > enabled the tower to be erected within tolerances per section 7.11
> >Frame
> >> > Tolerances of the 1986 AISC Code of Standard Practice was by welding
> >> > instead of bolting the braces to the beams.
> >> >
> >> > What may have caused the bolt holes to be so mismatched? The base
> >plates
> >> > for the columns had been positioned within the erection tolerance of
> >plus
> >> > or minus 1/8-inch of the design elevation per section 7.6 Bearing
> >Devices
> >> > of the AISC Code of Standard Practice. The wide-flanged beams,
columns
> >and
> >> > braces had been milled and fabricated within the tolerances per ASTM
> >A6.
> >> >
> >> > Does the accumulation of mill, fabrication and erection tolerances
> >> > preclude using bolted braces with standard round holes unless extra
> >> > measures are taken beyond standard construction? Do base plates need
to
> >be
> >> > exactly at the design elevation with no plus or minus 1/8-inch
> >tolerance?
> >> > Do bolted braced frames need to be assembled in the shop by the
> >fabricator
> >> > to insure ease of erection by the erector? Does the contractor
always
> >need
> >> > the option of welding the braces?