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    Default Roof Construction Pic



    So, what EXACTLY is this roof construction called? I've heard so many different things, I want the facts!

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    We call them bar joists in my line of work (the one that pays the bills). Probably a million names for them though...

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    Default Ummm...

    To me it looks like an older version of "trust construction".

    Feedback on that please.

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    Wink roof construction

    um......... looks to be metal bar joist truss, with a corrugated metal deck.

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    Lightweight steel bar joist trusses with a corrugated roofing deck, with either a ribber membrane or tar and gravel roofing surface.

    "Never trust a truss"!
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
    Lt. Ray McCormack, FDNY

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    It does appear to be a steel bar joist, however, a second look at the top rail almost appears to be wood 2x4 or 2x6. Same with the bottom.

    Perhaps the webs are bolted through. If this is the case, it's a new one on me.

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    Perhaps the decking is made of aluminium. Aluminum and steel do not like each other very much...galvannic reaction!
    Last edited by CaptainGonzo; 07-29-2004 at 09:40 AM.
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
    Lt. Ray McCormack, FDNY

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    Near as I can see it's all steel bar joint with the corrugated roof bolted right to the joists. I think the flange is rather exceptionally large which is giving the look of the wood. I could be wrong about that though.

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    what EXACTLY is this roof construction called
    Built to fail?
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Unhappy

    LODD Decking.
    I think everyone is honing in on the same concept. Around here we call it "Parallel chord open web steel bar truss". Most new industrial/commercial construction around here uses this. I imagine a heated argument could weaken it!
    On the brighter side, at least it's exposed where you can see it. (unless it's concealed in smoke). Imagine hiding that behind a drop-ceiling. It's like a booby trap- get a fire up in the concealed space which backdrafts, blowing the aluminum ceiling grid down on onyone inside....(Shudder)It's happened before.....
    Hopefully by the time you pull up to a fire in this building it's either a contents fire you can douse with the water can, or it's so far gone all you have to do is put up the tower ladders and hose off the foundation. Going inside for a search or interior attack has some big-time pucker factor going for it.

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    Steel Truse and "Q" Decking
    IACOJ Member

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    Originally posted by E229Lt
    It does appear to be a steel bar joist, however, a second look at the top rail almost appears to be wood 2x4 or 2x6. Same with the bottom.

    Perhaps the webs are bolted through. If this is the case, it's a new one on me.
    I saw that and thought that the flanges of the truss were U-channel. I can see some likeness to wood. Perhaps the original poster could enlighten us as to the materials of construction.

    Edited because I looked at the picture again:

    Artie,
    Notice that the metal decking ("Q" decking) has the same mottling as the flange on the truss, I am leaning more towards the steel U-channel now, but the mottling does look like knots in the picture.

    Edited again to change web into flange, which is what I really meant.
    Last edited by Lewiston2Capt; 07-29-2004 at 05:20 PM.
    Shawn M. Cecula
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    IACOJ Division of Fire and EMS

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    This photo shows the underside of the roof of a building built in the late 60's/early 70's.

    The white beam across the bottom of the picture is actually a light fixture.

    There is no wood in the photo. The joist is steel, as well as the metal "Q" decking.

    Could I get some definitions for clarification?

    Mottling?
    Flange?


    I would like to draw a distinction between this type (it seems steel bar joists is a pretty agreeable term) and a full lightweight aluminium truss. I've seen both, and I think I would much rather be under a steel bar joist...

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    Originally posted by Pride373
    This photo shows the underside of the roof of a building built in the late 60's/early 70's.

    The white beam across the bottom of the picture is actually a light fixture.

    There is no wood in the photo. The joist is steel, as well as the metal "Q" decking.

    Could I get some definitions for clarification?

    Mottling?
    Flange?


    I would like to draw a distinction between this type (it seems steel bar joists is a pretty agreeable term) and a full lightweight aluminium truss. I've seen both, and I think I would much rather be under a steel bar joist...
    Mottling is the discoloration on the underside of the deck. It will not have a big affect on the strength.

    Flange probably refers to the top and bottom horizontal member of the truss, although chord is a more correct term for that, technically. A flange of an I beam is the top and bottom member of the I.

    You actually don't want to be under or on top of any type of truss in a fire. Aluminum, to my knowledge, is not used in these types of trusses except for possibly non-load carrying applications. Steel bar joists perform very poorly in fire conditions and will fail without warning.
    Thomas Anthony, PE
    Structures Specialist PA-TF1 & PA-ST1
    Paramedic / Rescue Tech North Huntington Twp EMS
    The artist formerly known as Captain 10-2

    No, I am not a water rescue technician, but I stayed in a Holiday Inn Express last night.

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    Post Info

    Try this link for a little information on Bar Joists.

    http://www.mc2-ice.com/popular_conve...bar_joists.htm


    47
    Thanks, Nathan

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