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Stirrups query

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  1. #1
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    Default Stirrups query

    I've got holes dug 600mm below grade, holes are 720 deep but the first 120mm is topsoil. I've bolted the "J" bolts to the bottom of the 600mm stirrups which has added 100mm to the stirrup depth.
    Before I start squaring things up and dropping the posts into the holes how much concrete needs to be below the "Js" and how much of a stirrup above ground is too much?
    I can dig deeper quickly enough to get another 100mm or so
    Stump holes are 500mm deep allowing for a 100 pad underneath each stump
    "A big boy did it and ran away"

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  2. #2
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    Man ... you got me stumped

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    Quote Originally Posted by Marc View Post
    Man ... you got me stumped
    Good Lord. Not bad tho. What stirrups are you talking about. Do you mean ones like these. If so what are you using a J bolt for. Just keep the horizontal part about 50mm above finished concrete.

  4. #4
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    Standard Pryda post stirrups, no need for the high wind version.
    https://pryda.com.au/product/full-stirrup-post-anchors/
    I've always used "J" bolts or similar with these, threaded rod if I have any offcuts
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  5. #5
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    OK
    I found the information I wanted in a different PDF from Pryda.
    Just an FYI. Minimum embedment depth 68mm or as specified by an engineer, deeper is better, maximum height above ground is 300mm, minimum is 135mm and lower is stronger. Nothing so far about any minimum depth below the stirrup but if it's the same as a stump footing and 100mm I'm plenty safe
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    Quote Originally Posted by Moondog55 View Post
    I've got holes dug 600mm below grade, holes are 720 deep but the last 120mm is topsoil. I've bolted the "J" bolts to the bottom of the 600mm stirrups which has added 100mm to the stirrup depth.
    Before I start squaring things up and dropping the posts into the holes how much concrete needs to be below the "Js" and how much of a stirrup above ground is too much?
    I can dig deeper quickly enough to get another 100mm or so
    Stump holes are 500mm deep allowing for a 100 pad underneath each stump
    if the last 120mm is topsoil then it sounds like you are into fill, you need go deeper to get into better material or increase the bearing area of the footing so yout don't get subsidence problems later on.
    Inter

  7. #7
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    Moon ... so you dug 720 deep only to find 120mm of top soil at the bottom of your hole. You are using J bolt and then concreting a 600 mm long stirrup down there for a stump that will have a 100 mm pad? ...

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    Quote Originally Posted by intertd6 View Post
    if the last 120mm is topsoil then it sounds like you are into fill, you need go deeper to get into better material or increase the bearing area of the footing so yout don't get subsidence problems later on.
    Inter
    Top soil is on top. I just don't count topsoil as part of a foundation hole, and the hole is in solid stuff, down through the marl layer into the basalt. My bad, it should read "the first 120mm"
    I've just fixed that mistake in the OP
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  9. #9
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    OK, about time.


    Relax Moon, have fun.
    What's with the J bolts? is the stirrup bottom plate going to be on top of the concrete and that is why the J bolt? Or are you concreting the stem of the stirrup?

  10. #10
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    Quote Originally Posted by Moondog55 View Post
    I've got holes dug 600mm below grade, holes are 720 deep but the first 120mm is topsoil. I've bolted the "J" bolts to the bottom of the 600mm stirrups which has added 100mm to the stirrup depth.
    Before I start squaring things up and dropping the posts into the holes how much concrete needs to be below the "Js" and how much of a stirrup above ground is too much?
    I can dig deeper quickly enough to get another 100mm or so
    Stump holes are 500mm deep allowing for a 100 pad underneath each stump
    I know a guy who can help you with the problem you have created, I can give you his number


    dcs-36732.jpg
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  11. #11
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    Engineer for the carport specified "J" bolts for the stirrups on those posts so I'm just going on previous advice, mind you those holes were over a metre deep and a big roof area.

    TBH I don't remember what the stirrup length was used there, "J" bolts would now make sense if they were short stirrups and therefore not deep enough into the holes.
    Oops, well it's only a few dollars.
    I can always take them off and keep them for something else
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  12. #12
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    Do what the engineer told you to do. I am just trying to understand what you are doing.
    Bolting down the bottom plate of those stirrups is the usual practice, unless you want to concrete the stem in the concrete ... (where else right?)
    In that case, the bolts are redundant since it is the plate, or rather the weld between plate and stem that keep the stirrup from going up.
    A carport is supposedly light? so you need to anchor it down properly.

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    I think that the operative wording in the pryda PDF is the phrase "Embedment depth as determined by an engineer" and the engineer in question being a private building surveror erring on the side of exteme cauion rather than risk the possibility of being sued at some time in the future.
    There was nothing "light" about the carport build, especially compared to most of the builds around here.
    I just took the "J" bolts off.
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    Quote Originally Posted by METRIX View Post
    I know a guy who can help you with the problem you have created, I can give you his number


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    Mate don't joke about that. Some engineers are making us go that deep now.

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    OK, you took the bolts off ... but I still don't know if you are embedding the stirrup in concrete or not and how far down. Usually those stirrups with a perforated base are to bolt on top of existing concrete, and the one with a solid stem and the end slightly bent, are for concreting (embedding) in concrete, no bolts needed.
    Both are relatively crappy since they rely on a light weld, but solid stem of course beats the hollow one but still has poor lateral stability.
    The high wind are the best of both world, good anchorage and solid lateral bracing

  16. #16
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    Quote Originally Posted by sol381 View Post
    Mate don't joke about that. Some engineers are making us go that deep now.
    That's because they have shares in the local concrete company
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  17. #17
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    Holes are 600+ deep and stirrups are 600mm high.
    If I use the minimum above grade distance of 135mm then the embedment depth will be 600-135 or 465mm.
    Naturally all the topsoil is going to be scraped away.
    I assume the Pryda tables for uplift are accurate so more than strong enough for our purposes
    Just one question tho. Bolts are stronger but is the new star drive construction screw stronger or weaker than a similar size coach screw? They are much easier to use and securing posts to post supports is one of the stated uses
    .bunnings.com.au/buildex-18-8-x-50-mm-zinc-alloy-3-star-head-timber-construction-screws-100-pack_p2410366
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  18. #18
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    Forget about the screws. Bolt it. Only way to do it. Screws are not for stirrups. Id keep the bottom horizontal part of the stirrup 50mm above concrete. !35mm seems way too high to me as those stirrups are PIss weak. Also what are you building if you havent already stated.

  19. #19
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    Replacing the old pallets with something a bit stronger at the back door. Been using S/H pallets since we started the project 7 years ago.
    I know bolts are thought to be stronger but in the Pryda spec tables 4 * 50mm coach screws are rated the same as 2 * 10mm bolts and the construction screw use a much tougher steel than a cheap gal bolt.
    I asked because they are much quicker to use and a lot cheaper
    You may be correct about the height above the base, I have an newer set of tables [2017] open in front of me which says 75mm minimum clearance.
    Why do you consider these post stirrups so poor? They are compliant and every builder around here uses them and I've not seen anything stronger in a long time and thir only job is to hold a post down against wind load.
    The landing itself is going on concrete stumps
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  20. #20
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    Mate just personal preference. I just dont think the single metal pole has much strength. Ive always used the U post type like i pictured above. If its for light use i think yours are ok but if doing a deck or something carrying a lot of weight i wouldn't touch them . Ive seen quite a few bend under the weight and pressure. Id suggest just go with bolts. They are probable cheaper than coach screws and clamp the stirrup against the wood.
    As for clearance that would probably be to the bottom of the timber post, which i leave about 25mm from the bottom of the stirrup.

  21. #21
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    Quote Originally Posted by sol381 View Post
    Mate just personal preference.
    As for clearance that would probably be to the bottom of the timber post, which i leave about 25mm from the bottom of the stirrup.
    I get personal preference.
    I don't understand the use of the 25mm gap tho, it makes the assembly non-compliant according to the pryda website.
    I have a problem with getting the holes square when hand drilling which is why I considered the screws in the first place.
    Anyway a chippie mate is dropping in soon to give me a hand, I'll do whatever the expert advises, even if it means more work on my part.
    "A big boy did it and ran away"

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  22. #22
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    well with the U stirrup the post doesn't sit on the flat bar. Not sure with the post stirrup youre using. I never use them If i says to sit it on , do it. Are you concreting the stirrup first or bolting to post then concreting together. Stirrup alone in concrete would be easier. If you drill from both sides using a 13mm steel bit then it makes it a lot easier. Whatever works mate.

  23. #23
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    My mate The Duffman prefers to make the assembly first then put it into the holes, set everything square and plumb and then concrete. That's what I have been doing today.
    Now waiting for the concrete to set and in a days time I'll start putting down the joists and framing up the roof.
    Just a small landing 2400mm deep and 2700mm wide, because that was the length of the decking boards we got cheap.
    It's so much faster and easier when you have a professional helping you and all you have to do is the hard donkey work, I did manage to get all the holes in the correct places and I'd bought enough of everything. He thinks my professional skills in the kitchen are of equal value to his carpentry skills so he gets paid in chicken curry and cheesecakes for this small [ 4 hours] job.
    "A big boy did it and ran away"

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  24. #24
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    Sounds like a sweet deal. Chicken curry. Nice.

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