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RE: Joints in concrete floor slab on bar joists[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Joints in concrete floor slab on bar joists
- From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
- Date: Mon, 26 Jul 2004 17:03:07 +0000
Bill,Short span elevated slabs have been designed for many years as "plain concrete" in the commercial building world. The SDI recommended reinforcing steel used in elevated slabs on metal decks is more for crack control and may not meet the ACI requirments for crack control. Many of these buildings have been in service since the 1950's. Almost all of the 1950's and 1960's shopping malls used form deck with temperature reinforcing only. I was involved many years ago in shopping malls even in your neck of the woods (Denver). You have done a lot of your Christmas shopping on unreinforced concrete floors.
Early composite metal deck had WWF welded to metal deck. The shipping costs were too high to gain wide acceptance. Only in the early 1980's did the trend shift to composite concrete metal floor deck when deck manufacturers used rolls to deform the sides of the metal deck to create a composite deck that could be stacked and shipped the same as regular form deck.
The problem comes about when NO crack control steel is used or if the contractor tries to substitute polypropylene fibers. The aggregate interlock is lost and then the model can become a cantilever as opposed to a simple span. There has been a lot of research at SDI and SDI members to substantiate the use of concrete slabs on form deck with only temperature steel. The safety factor is also fairly generous
With all of that, today I would be very judicious about where I would use a form deck and plain concrete slab today. But I have used them in my early career.
Regards, Harold Sprague
From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com> Reply-To: <seaint(--nospam--at)seaint.org> To: seaint(--nospam--at)seaint.org Subject: RE: Joints in concrete floor slab on bar joists Date: Tue, 20 Jul 2004 09:49:28 -0400 Several responses note to check the slab as an unreinforced section, as "plain concrete". Is this permissible for an elevated slab? Admittedly the weight of the slab is supported by the metal deck but I'm not sure that is equivalent to the support given a slab on grade. If the metal deck can only support the concrete dead weight but not the live load and if the plain concrete cracks, won't the deck then need to support both the dead load and live load? Is that a safe design? I generally don't use "plain" concrete, so I am not clear on what the code permits in such circumstances. William C. Sherman, PE (Bill Sherman) CDM, Denver, CO Phone: 303-298-1311 Fax: 303-293-8236 email: shermanwc(--nospam--at)cdm.com ________________________________ From: Stuart, Matthew [mailto:mstuart(--nospam--at)schoordepalma.com] Sent: Thursday, July 08, 2004 2:27 PM To: seaint(--nospam--at)seaint.org Subject: RE: Joints in concrete floor slab on bar joists I don't know what your live load criteria is but my hunch is that when you run the numbers the slab section will check as an unreinforced section under the provisions of ACI 318 Structural Plain Concrete. D. Matthew Stuart, P.E., S.E. MASCE/SEI/BPAD Senior Project Manager Schoor DePalma Engineers and Consultants 200 State Highway Nine Manalapan, NJ 07726 732-577-9000 (Ext. 1283) 732-431-9428 (Fax) 908-309-8657 (Cell) mstuart(--nospam--at)schoordepalma.com -----Original Message----- From: DSmith7367(--nospam--at)aol.com [mailto:DSmith7367(--nospam--at)aol.com] Sent: Thursday, July 08, 2004 4:17 PM To: seaint(--nospam--at)seaint.org Subject: Re: Joints in concrete floor slab on bar joists Matthew: Thank you for the reply regarding the slab problem. The slab is on light metal slabform spanning two feet between bar joists. How would you add sub framing? It would be tough. The same with external reinforcement. Regards, Dave Smith
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