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RE: GLB v. Open Webbed Steel Joists

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In reply to your second point;  SJI requires attachment to the perimeter
(CMU) with the same specification as interior fastenings; i.e. 36/7
attachment with 5 sidelap fasteners per span would require 7 welds at
all bearing ends of the deck (at the CMU) and 5 sidelap fasteners at the
non-bearing edges (at the CMU) all around the perimeter.  This precludes
the code requirements and is applicable in all usage of metal decking
diaphrams and steel bar joists.

One must also be aware of the code requirements for attachment to the
CMU in order to support the "pin connection" support at the top of the
wall.  I have seen projects where the diaphram loads where so small that
side lap fasteners were not specified in order to avoid installing a
perimeter angle along the non-load bearing walls.  The LA requirement
for subdiaphrams seems excessive.  It is assumed that the framing is
sufficiently anchored to the CMU.  The subdiaphram design was developed
to ensure that the framing is sufficiently anchored into the diaphram.
Section 1633.2.9.4  states that chords of subdiaphrams MAY be used to
transmit the anchorage forces to the main continuous crossties.  The
idea with a wood diaphram is to transfer the loads into the diaphram in
as short a distance as possible in order to have the minimum nailing
requirements across the majority of the deck and only increase the
nailing at the localized perimeter in order to handle the attachment to
the wall for support of the CMU.  

Metal decking attachments compared one on one to nails are much
stronger.  If your minimum weld/attachment spacing gives you the
required plf to support the masonry walls (and your truss top chord is
continuous from wall to wall, this is accomplished simply by calculating
the axial load and make sure that you bolt/weld attachment to any
interior beams can handle this force) then the theory behind the basis
for the code justifies design of the deck without a subdiaphram.  Of
course, trying to explain this to the building department would be
futile if they have made up their minds.  What I have done in the past
was to explain my engineering defense and challenge them to show you the
code that proves you wrong. 

-----Original Message-----
From: cmh(--nospam--at)wallacesc.com [mailto:cmh(--nospam--at)wallacesc.com]
Sent: Wednesday, September 15, 1999 10:38 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: GLB v. Open Webbed Steel Joists


I have encountered two problems with permitting plans using open web
steel
joists in California.  The first problem is with the submittal of the
joists during the permitting process.  Plan checkers will frequently
require the joist manufacturer to sign and seal their erection drawings.
Vulcraft does not object to signing and sealing their calculations, but
refuse to sign and seal their erection drawings.  The plan checker then
expects me to sign and seal the manufacturer's erection drawings, which
I
refuse to do since the joists are not designed by me.  Also, some plan
reviewers have also required that the joist manufacturer submit
elevations
of each of their joists, identifying member sizes on each elevation as
if
it were a manufactured wood truss.  This is unusual to me since the
steel
joists were preapproved and published in the 1994 UBC as acceptable (as
long as SJI monitored the joist manufacturer).  I have used steel joists
elswhere in the country for years without this kind of resistance.  Most
of the plan reviewers act as if open web steel joists are some kind of
new
invention that they must regard with suspicion - a very unusual attitude
since steel joists have been around for a very long time.  I also get
the
same attitude with regard to the use of steel deck diaphragms.
The second problem I have with steel joists and steel deck diaphragms is
the issue of wall anchorage to concrete or masonry walls.  LA requires
wall anchorage details very similar to that required for wood roofs
(i.e.
sidewall subdiaphragms created with the use of steel angle struts
perpendicular to the wall at 4' o.c.).  Others believe that this is
unnecessary.  No testing has been done and I am not aware of any
anectdotal evidence from past performance in earthqakes.  It would be
helpful if their was some consistent policy regarding wall anchorage
when
using steel joists and metal deck.

Thanks,
Christopher M. Harris, P.E.