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RE: Cost Analysis

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I too am very interested in this framing type for a number of reasons. We too have used this type of constr.  many, many times with  pretty good success.  The typical problems we see is green load deflection of the beam (purlin) and girder.  We recently switched to RAM and can design an entire bldg in short order.
 
Since no one likes shoring and  is variable by definition, we now are using a minimum camber for the purlins and designing for maximum 1/2 " green load defl in girder.
 
We are very concerned about getting more camber in the purlins than what we specified, and thereby getting a too thin slab where the conc is screeded level(using a lazer screed),  or a wash-board slab if the conc is screeded 'constant thickness'(using screed rails).
 
Incidentally for our most current job our bay size is 32X40 and we are using 2"X20 ga comp deck with purlins @ 8'.
 
So my question to the readers at large is this:    >>
 
HAS ANYONE ENCOUNTERED A MAJOR PROBLEM WITH CAMBERING ONE DIRECTION FOR COMPOSITE BEAM FRMG??___________________
 
 
 thx  David
-----Original Message-----
From: HAWNENG(--nospam--at)aol.com [mailto:HAWNENG(--nospam--at)aol.com]
Sent: Thursday, March 22, 2001 10:28 PM
To: Seaint(--nospam--at)seaint.org
Subject: Re: Cost Analysis

Jason,

I believe spacing the wide flange girders @ 6'-0" to 8'-0" is greatly under
utilizing the system - materials.  We engineer a lot of buildings of this
type of construction.  Ideally, you want a 30'-0 x 30'-0 column grid (28'-0
to 32'-0 spacing range).  Space W24 girders @ 30''-0 o.c. then uniformly
space the beams, W14 or W16's, @ 10'-0 between the W24 girders.  Use 18ga -
W3 deck with 2.5" of lightweight concrete fill over the top of the flutes.  
Total thickness of the deck and fill is 5.5".  This also provides a 1 hour
fire-resistive assembly.  The deck will span 10'-0 unshored.  Anything much
less than this span is inefficient for the deck.  We also typically design
for 52 to 55 psf dead load + 20 psf partition load + 80 psf live load.  This
system works quite well.   The column size is usually a W10, however, if you
are crunched for space, you can make W8's work (assuming this is only a two
story structure).   

I am also an engineer who "dislikes" open web joist systems so, admittedly, I
am  quite biased.  Please let me know the outcome of your cost analysis.

Greg Showerman, S.E.