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RE: Steel Roof Deck Attachment Question

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Charlie:

I have been dealing with this issue for the past month.  We have a recently
constructed 200,000 s.f. industrial building project that is concrete
tiltwall construction with a steel diaphragm roof deck supported by open-web
steel joists and joist girders.  At certification time, we discovered that
the roof construction had never been inspected.  Upon removing about 1% of
the roofing to perform an inspection after-the-fact, we discovered that the
deck was inadequately connected to the joists and, as constructed,  was
capable of transmitting only about 55% of our design shear forces.  Repairs
would be necessary before the building could be certified, and time was of
the essence because a contract was pending for the developer to sell the
building.

We proposed removal of the roofing, followed by inspection and repair from
above.  The contractor objected, on the basis that this would cost more than
$500,000 and result in nasty litigation.  He proposed installing "pop
rivets" from below.  We objected, on the basis that we could find no
evidence that the proposed rivets, which are intended for use in the
manufacture of truck bodies, would adequately clamp the 22 ga. steel roof
deck to the chords of the joists.

Finally, we found two products that we were able to accept for making
repairs from below the deck.  They are GESIPA Olympic Bulb-Tite Rivets and
FABCO (Camcar Textron) Fab-Lok Fasteners.  I would describe both fasteners
as being "industrial strength molly bolts".  Repair work commenced this week
using the Fab-Lok Fasteners.  If you use either of these products, please
note that:

1)  The shear strengths quoted in the manufacturer's literature are
irrelevant.  This is for direct shear across the throat of the fastener, as
if two relatively thick pieces of steel were being connected.  For the
connection of roof deck, the reliable clamping force is much more important.

2)  Flanges of your W shapes are much thicker than the thicknesses of our
Vulcraft joist chord angles.  Pay attention to the exact dimensions of the
fastener you select, and ensure that it can handle your thickness.  Also,
the relatively narrow width of the deck flutes will influence your fastener
selection.

3)  Make multiple tests and carefully observe the results before proceeding
with the overall construction.  We stripped off a chunk of roofing this week
and observed from above and below while the contractor installed the first
20 (+/-) fasteners (of nearly 50,000 required).  We worked with the
contractor to determine what procedures gave the best results.  Among other
things, we concluded that the fasteners were only reliable with one ply of
decking, so we adjusted the repair pattern to avoid side laps (2 plys), end
laps (2 plys), and corners (4 plys).     

4)  You will find that these fasteners are quite expensive when compared
with typical steel deck fasteners installed from above (puddle welds, seam
welds, powder actuated fasteners, and tek screws). 

5)  Special installation tools are required, and they might not be readily
available.  At least, not until our project is completed!;^>

I hope that this information is useful.  If you want more detail, just
contact me privately by email or telephone.

Regards,

Stan R. Caldwell, P.E.
Vice President
*************************************
HALFF ASSOCIATES, INC.
Engineers+Architects+Planners
8616 Northwest Plaza Drive
Dallas, Texas    75225
Phone:  (214)346-6280
Mobile:  (214)236-9696
Fax:      (214)739-0095
Email:   scaldwell(--nospam--at)halff.com 
Website:  http://www.halff.com
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