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RE: STEEL: Lateral Support for Open-Web Steel Joists[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: STEEL: Lateral Support for Open-Web Steel Joists
- From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
- Date: Wed, 04 Aug 2004 22:07:40 +0000
Bill,Your trepidation is warranted. I would rather face the client's wrath than his lawyers.
I would not use bar grating to act as a lateral support for the bar joist top chord (the answer is no). I would definately not use it with saddle clips (the answer goes to Hell NO!).
The first option would be WF with bar grating and design the beams for whatever bracing worked out as most economical. If you have to go to bar joists, provide secondary bracing. You should be able to get some backing from the joist manufacturer. There is just no data of which I am aware that would support using bar joists to serve as top chord bracing.
On your last point, call the joist manufacturer for input. Or you could suggest a confirmation load test. For a 200 psf LL you would need to apply about 300 psf.
Some time ago I wrote a letter to a very high profile client that told him that his building was not safe for human occupancy. ...piece of cake. Of course that client no longer uses us, but I sleep well. Good luck!! So the choices are eat or sleep? ;>)
Regards, Harold Sprague
From: "Bill Polhemus" <bill(--nospam--at)polhemus.cc> Reply-To: <seaint(--nospam--at)seaint.org> To: <seaint(--nospam--at)seaint.org> Subject: STEEL: Lateral Support for Open-Web Steel Joists Date: Wed, 4 Aug 2004 16:00:15 -0500 Greetings.
I have a job that requires adding on a couple of bays to a mezzanine level in an auto parts supply warehouse. The existing mezzanine level has steel bar grating supported on K-series steel joists. The real kicker is that the floor is rated (sign is posted) at 200 psf! Yet the bar grating is attached to the top chords of the joists usingtypical "saddle clips" (e.g. http://tinyurl.com/6gkdp, illustration at upper left), which IMO will not provide adequate bracing against lateral torsionalbuckling of the joists under service load. Further, the bridging provided for the K-joists appears to be the standard for construction phasing before a solid deck is put down. First, am I misinformed about the ability of the bar grating with only saddle clips to brace the joists? Of course the owner would say "hey, it's worked this way for several years, never had a single problem yet! And will want me to put into the new addition exactly what is already there.Second, what would be best: Use K-joists still, but make sure that the joistsupplier puts adequate cross-bridging to assume there is no lateral torsional buckling problem? Or use wide-flange girders? I'm tending toward the first option because I could probably quietly slip it by without the owner's curiosity being piqued. Finally, what is my ethical responsibility with regard to the joist-supported floors which (if my assessment is correct) are not adequate for the posted load? This place is actually within the city limits of asmall, well-to-do south Texas town that actually has a building official. DoI need to bring this up to the owner and inform the building official (thus possibly incurring wrath?)This business is a high-profile outfit. I wouldn't be surprised, in fact, ifthe building official didn't choose to look the other way even if I did complain. Sheesh.
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