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Too Big Bearer Span

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  1. #1
    Apprentice (new member)
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    Jan 2009
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    Default Too Big Bearer Span

    Hoping you can provide some guidance - not sure if I have been misled!!

    Building a floor for a cubby house, total size 3.0m x 2.2m.

    With bearer span being 3.0m and wanting to get away with post at either end only (no post in the middle), I consulted span tables which suggested I needed at least 150x50. All good to this point....

    I then headed out to buy timber. I was talked out of 3m x 150x50 and was told instead to go 2 pieces of 3.0m x 90x45 treated pine and screw them together (to effectively create 90x90). These have been bolted to the cyprus posts.

    The frame for the floor is now together and I am worried that I am getting too much flex. Am I pushing my luck with 3.0m span with this wood?? It will mostly only be 2 kids in the cubby (plus weight of cubby, of course), but I want to be sure it will be safe.

    Comments, thoughts, advice please?

    Thanks.

  2. #2
    Hammer Head - 1K Club Member
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    Default

    wack a post in the middle, even just concrete in a post shoe

  3. #3
    Deck Builder
    Join Date
    Jun 2008
    Location
    Launceston
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    33

    Default

    What he said.

    The structure won't fail, just flex. It's not dangerous.

  4. #4
    Apprentice (new member)
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    Default

    Thanks for the advice.

    Flex isnt significant, unless I am really trying!! Just wanted to make sure.

    How do the post shoes work? Assume I need to dig a hole for the concrete first? And is there any easy way to do that with the structure sitting over the top??

    Sorry for all the questions - absolute newby at this!!

  5. #5
    Deck Builder
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    Jun 2008
    Location
    Launceston
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    Default

    If you have to try hard to get the bearer to flex then it really doesn't need any extra support, but since you've asked....

    A post shoe or post support or post stirrup is a metal bracket attached to a length of pipe and is designed to bolt to the base of a post to anchor the post to the ground. Ask at any hardware store and they'll show you one, then sell you one! About $10.

    Dig a hole halfway along the bearer's span - no tips on how to do this!

    Make it about 400 deep and 400 square. Bolt your post support to the beam with the bottom of the post hanging inside the hole. Fill the hole with concrete - rapidset will be fine.

    All this assumes your bearer is close enough to the ground for a post support to reach at least 100mm into the hole. The longest supports are about 300mm.

    If a support won't reach just use a timber post instead.


    Regards

    Damien

  6. #6
    Apprentice (new member)
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    Default

    Thanks Damien.

    Was really hoping there was an easy way to dig that hole - the bearer sits about 100mm from the ground so digging under it could be interesting. That said, think I will just see how she goes. Had the wife and two kids in the cubby with me tonight and seemed OK.

    Thanks heaps for your advice.

  7. #7
    Senior Member
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    Apr 2006
    Location
    Melbourne Victoria
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    Default

    Span tables for decks are probably overengineered for a cubby. Decks could expect a party, BBQ etc. Cubbies would have a much smaller load. You probably would get away with what you have.

    Most strength is in the depth i.e the 150. The 50 stops it twisting and would have been better.

    Many cubby places don't even dig holes for their stumps and just rest them on the ground. Some elevated ones have small holes and put a surround around the 4 posts to make a sandpit.

    If you wanted you could probably get away with a fairly shallow stump hole and concreting in a stirrup. Even a couple of bricks stacked on solid ground may be enough

  8. #8
    Apprentice (new member)
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    Default

    Thanks Brian, unfortunately a little too late!!!

    The cubby went up last weekend, complete with post holes 500 deep, with very solid cyprus posts (was originally going 90x90 tp, but based on lengths needed, and wood available, was cheaper to go the cyprus). Based on what you said, total overkill!!

    But I do at least like the idea of sinking them into the ground - while the weight of the cubby would keep it on the ground, it seems better to get it off the ground. Plus SWMBO wanted a 1.2m deck out the front, so I had to rig up frame for that anyway.

    Really grateful for all the advice - if only I had known about this site on the last few jobs!!

    Viginti.


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