Pratt type truss
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  1. #1
    Join Date
    Jun 2017
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    AJO, ARIZONA
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    1,110

    Pratt type truss

    Recent winds and other things have mandate that I restructure my carport, it is about 25x25, give or take a foot. It currently has a center truss that is 2 x 8 lumber that has 2 support posts about 8 ft in from each end. I have to resheet the roof and incorporate some slope. I would very much like to eliminate the 2 support posts and span the 25 feet with just support on each end, it will be sheeted with OSB and covered with roll roofing, I need to build a PRATT TYPE TRUSS for it and am curious as to what size pipe I can use.
    Thanks guys,
    Jeff
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  2. #2
    Join Date
    Mar 2018
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    Stokes County, NC
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    Re: Pratt type truss

    Hi Cavemann

    I appreciate that this is a welding site but have you given thought to pricing new full span wooden trusses? We built a 54x108' Morton steel pole barn three years ago. It has 56' long 3 in 12 pitch trusses on 9' centers in an area where we built to 55 pound per square foot snow load. The extra 2' of length allowed for a one foot overhang for soffit vents. The lower chord of the trusses were slanted up so there was about 4' more overhead clearance in the center of the building than at the walls.

    25' trusses (or 27' with a foot overhang for soffit vents) shouldn't be too pricey as they are pretty standard garage truss sizes And you could have the trusses on, the roof deck nailed off and the place "dried in" in a weekend. All you'd need to do for prep would be to have the truss seats welded on, drill, bolt and diagonal brace the trusses as they were set and you'd be ready to install the purlins.

    If you went with trusses on 4' centers you only be looking at 7-8 trusses.
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  3. #3
    Join Date
    Jun 2016
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    Re: Pratt type truss

    2 x 2 3/16 with 2 x 4 14 ga. rafters I've used them as a ridge pole. 20 foot span to each side.
    It'll handle 6 toucans and 4 howler monkeys per square meter. Dunno about snow.
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  4. #4
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    Jun 2017
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    AJO, ARIZONA
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    Re: Pratt type truss

    Snow isn't a problem, I'm in southwest Arizona. I'm looking at something I can fab on site as it's at least 80 miles to the nearest place where I can buy wood trusses, they were my first thought, but I have no way to haul them & figure shipping would kill the deal. I only need 1 truss with the layout of the building. I just want the 2 posts gone because they are always in the way when getting in & out of the truck.
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  5. #5
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    Jun 2016
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    Re: Pratt type truss

    Caveman....got any pics ?

  6. #6
    Join Date
    Jun 2017
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    AJO, ARIZONA
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    Re: Pratt type truss

    No pics, my father in law originally built it, and it has 2x6 center truss with the 2 posts, with 2x4 joists(perlins) on 2' centers on an 8'span with 3/8 plywood sheeting, no slope and the 2x4's and some of 2x6's are sagging badly so it's a lake on top when it rains, to top it off he nailed the roofing with the shortest roofing nails he could buy, so I want to replace the center truss and upgrade the 2x6's to 2x8 and the 2x4's to 2x6 and 15/32 osb sheeting and slope it a foot in 25 feet.
    NRA LIFE MEMBER
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  7. #7

    Re: Pratt type truss

    You may want to using a wide flange beam or I beam
    Now you put Hoist on beam

    Dave

  8. #8
    Join Date
    Nov 2009
    Location
    Seward, Ak
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    295

    Re: Pratt type truss

    Got to the nearest lumber yard and tell them what you want and let them design the truss for the roof system you need. Get the specs and go to the next place over and buy the material, set up and build the 1st truss. Us it as a jib for the rest of the units.

  9. #9
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    Dec 2007
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    Re: Pratt type truss

    Quote Originally Posted by akpolaris View Post
    Got to the nearest lumber yard and tell them what you want and let them design the truss for the roof system you need. Get the specs and go to the next place over and buy the material, set up and build the 1st truss. Us it as a jib for the rest of the units.
    ?

    Why go to the next place to buy the materials?
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  10. #10
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    Nov 2009
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    Arizona
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    Re: Pratt type truss

    Quote Originally Posted by akpolaris View Post
    Got to the nearest lumber yard and tell them what you want and let them design the truss for the roof system you need. Get the specs and go to the next place over and buy the material, set up and build the 1st truss. Us it as a jib for the rest of the units.
    Well the original poster lives in Ajo, Arizona and I can tell you he is not going to find one, let alone two lumber companies without driving bout 100-200 miles. Even here in Tucson we don't have any real lumber companies left, Home Depot and Lowes put them all out of business and now we are stuck buying their "firewood" quality crap. If we need trusses we order from Phoenix.
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  11. #11
    Join Date
    Jun 2017
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    AJO, ARIZONA
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    Re: Pratt type truss

    Thank you bigb, people don't understand the problems of a tiny town like Ajo, we have a True Value and an Ace, both have lumber but the choice is limited,I want to do the pratt type truss because I can easily fab it on site, I don't need it to support anything but the joist I use, the OSB, underlayment and sheeting, and my weight while I am on it. It's a 25 ft span in the center of the carport with 12 ft joists on both sides.
    NRA LIFE MEMBER
    UNITWELD 175 AMP 3 IN1 DC MIG/STICK/TIG
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    GOD BLESS AMERICA!
    “Freedom is never more than one generation away from extinction.
    We didn’t pass it to our children in the bloodstream".
    RONALD REAGAN

  12. #12
    Join Date
    Mar 2011
    Location
    Western Washington
    Posts
    1,148

    Re: Pratt type truss

    I don't know if they are still around or not... could be even more now... but a few years ago I needed to design a truss and found a couple simple truss calculators online, very handy just input a few key details like span, PSF loading and height and voila instant truss drawing with dimensions of course this was for dimensional lumber trusses but might be something out there for steel...

  13. #13
    Join Date
    Jun 2016
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    by a resevior in north central ar.
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    161

    Re: Pratt type truss

    i live in northern arkansas and had a 30x50 pole barn built and they constructed trusses on site with plywood plated sections, held up thru a 24" snow!
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  14. #14

    Re: Pratt type truss

    Try this link for designing your truss. This helped me when I redid my 40 ft truss in my shop. That was 8" S beam for chain fall trolley. In the attic is 4" channel frame with 3x3 angle bracing. Checked all the stresses with this program and came out with the fasteners being the weak point, but the entire structure with support 5 ton safely.More that I can pull on the hoist chain. I know this may much overkill. Hopefully this helps.


    https://ei.jhu.edu/truss-simulator/

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