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RE: GLB v. Open Webbed Steel Joists[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: GLB v. Open Webbed Steel Joists
- From: "Jeffery Seegert (x 485)" <jbseegert(--nospam--at)matrixti.com>
- Date: Wed, 15 Sep 1999 12:58:48 -0400
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 16126.96.36.199 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.
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