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Re: Steel Deck Diaphragms

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Title: RE: Steel Deck Diaphragms
Robert:
 
I've used powder actuated deck fasteners for two projects. One project is a 60,000 S.F. grocery store near New Madrid seismic area. Due to poor quality of puddle welds found in other projects, I insisted on using Hilti ENP2K pin connections. There were resistance from the contractor and the owner. However, they accepted the pin connectors after I explained my design considerations. First, special inspection is required for deck connections due to the importance of diaphragm shear system in seismic area. As in many projects, deck welds seldom pass inspection at one shot. The cost difference between Hilti pins and puddle welds is not as much as it appears if one takes weld fixing and schedule delay into account. Another project I used pin connectors is a 105,000 S.F. tilt-up warehouse office building in St. Louis, Missouri. Cantilever wide flanges were used as girders supporting steel joists in order to achieve maximum ceiling height. Internal drains required sloped girders in addition to sloped joists. Therefore, deck wrapping occurs, which tends to create a gap between deck and joists. The quality of puddle welds is hard to maintain due to the gap. The owner was informed on this design consideration during preliminary design stage. They made informed decision. So, Hilti ENP2K or its equivalent was on the final drawings. Contractor found ITW's Powder Fastening System to be equivalent and cheaper than Hilti ENP2K. So, ITW's Buildex powder-actuated fasteners were finally used. Both of these projects were very successful. The pin connections were easy and fast to install and inspect. The owners were happy when the jobs were done.
 
From the experience of the two projects, I found that it is very important to inform and educate project owner at early design stage. By doing that, it is essentially the owner's decesion of using premium construction procedure. Therefore, the resistance from the contractors can be removed much easier.  
 
Also, in specify powder actuated fasteners, be very careful to coordinate supporting steel stiffness.
 
As I found in many job site visits, lots of puddle welds merely burned holes through deck. There is no physical contact between the deck and supporting steel. This often occurs when welder stepped away for next puddle weld immediately after finishing the previous weld. At that moment, the weld is very hot and possibly is still in melt stage. Therefore, the deck pops up when the weight of the welder moved away. 
 
Other poor construction often found in relating Steel Deck Diaphragms are:
         -----   Expansion bolts at deck edge angles are often untightened or left in un-grouted core of CMU wall even though the drawing clearly called
                 for grouting at all expansion bolts.
         -----   Bearing plates mismatch joists with little welds or no welds at all between joist and bearing plate. The roll-over diaphragm shear load path is
                 therefore disrupted.
 
Therefore, I usually call for special inspections to be performed for all field welds, expansion or epoxy bolts as per current BOCA code.
Without the said inspection to enforce design documents, no matter how much effort the engineers put into the design, no matter how advanced and sophisticated the code or design theory is, the buildings are just as unsafe as the one built with no engineering design at all. 
 
Jie Lu, P.E., S.E.
J. Lu International, LLC
St. Louis, Missouri
 
 
----- Original Message -----
Sent: Friday, April 23, 1999 2:54 PM
Subject: RE: Steel Deck Diaphragms

out of curiosity:

we always have uses the puddle welds due to local erectors resistance to it, but:
how many out there are specifying the required usage of powder actuated mechanical deck fastening ? hilti ENKP pins, etc ? in lieu of the good old puddle weld ?

who else beside our structural department always uses 20ga as a minimum deck thickness so you can always weld the sidelaps (logic being that if he's welding the attachments, he might as well weld the laps, rather than go get the drill gun?)



    -----Original Message-----
    From:   Roger Davis [SMTP:rdavis(--nospam--at)sdsarch.com]
    Sent:   Friday, April 23, 1999 1:24 PM
    To:     seaint(--nospam--at)seaint.org
    Subject:        RE: Steel Deck Diaphragms

    Steel Deck Institute says " Arc-spot welds, or puddle welds, are produced by
    striking an arc on the upper sheet, forcing a hole to form, while the lower
    unit is being raised to fusion temperature.  With the attainment of proper
    temperature, the electrode is moved in a pattern until the hole is filled
    and fusion atained on the arc-puddle perimeter."

    Roger Davis
    SDS Architects, Inc
    205 N. Dewey Street
    Eau Claire, WI 54703
    715-832-1605
    rdavis(--nospam--at)sdsarch.com


    -----Original Message-----
    From:   Christopher Wright [mailto:chrisw(--nospam--at)skypoint.com]
    Sent:   Friday, April 23, 1999 10:43 AM
    To:     SEAOC Newsletter
    Subject:        Re: Steel Deck Diaphragms

    >I have specified a 22ga. steel deck  with puddle
    >welds at supports
    For cultural value what is puddle weld?

    Christopher Wright P.E.    |"They couldn't hit an elephant from
    chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
    ___________________________| John Sedgwick, Spotsylvania 1864)
    http://www.skypoint.com/~chrisw




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