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Pryda Post Supports

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  1. #1
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    Default Pryda Post Supports

    Hello, I have been notified of this forum from a few customers requesting clarification on the installation of Pryda post supports. I was given directive to this forum and the thread in question regarded the installation of posts into high wind style post supports. I can see it looked all very heated. I thought the tech sheet was self explanatory but may need further investigation.

    I work for a distributor of Pryda but do not have authority from my employer to post here, so I am just posting as one man. With technical sheet in hand I called Pryda's engineering department and had one of their engineers go through the tech sheet with me.

    To clarify, the post support was never designed to have the posts only supported by the bolts as the capacities of the post support bracket itself was too low.

    The other thing that came into play was that 300mm maximum stem height or area sticking above the concrete. The post helps keep the sides of the post support rigid. It was found during testing that if the post is not bearing on the cross member, it creates a weak spot on the arms of the post support allowing for buckling and failure of the post support well before the maximum dead load noted on the tech sheet is achieved.

    As this GCB company installation guide was noted and they sell opposition products, I decided to call some stockists and asked for engineering. None was forthcoming. I then noted the fine print of their installation guide and it reads like this.

    "Installation must be accordance with local council building regulations and engineers(sic) specification."

    So from what I can assume with my limited search, there does not seem to be capacities for the GCB product. Now no doubt they are well made, but the few stockists I spoke to can not offer advise on the post support's maximum capacities when installing the post as per their guide. There must be a maximum capacity installing the post as per the GCB install guide, though what is it?

    When not supporting the post on the cross member Pryda's engineering team found failure well below the maximum capacity noted when bearing the post on the cross member. The failure was potentially low so they insisted on the bearing being used and didn't offer capacities without bearing.

    As mentioned I do have a vested interest in the Pryda product. I want you to buy one of the many products we distribute to the hardware markets under many different brands but we also want you to install them correctly. But please do not take my word for it. Please call the Pryda engineering department and have them clarify this for you in person. So there you have it. Straight from the horse's mouth, so to speak.


    And I did notice in that previous post the question was posed on when could it ever be wrong to go above specification on engineers drawings. Going up a size in bolts was an example. Straight away I though of bearer or ledger situations where the size of the ledger is determined by the safety factor either side of the bolt. If the bolt size was increased by the person installing without advising the engineer, there may not be enough timber either side of the bolt and the timber could split.


    Well I'm off to go see what goodies I can dream of doing to my old place in tarragindi. great site here.

    thumbs

  2. #2
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    Hi thumbs, thanks for the info and being so open re your affiliations.

  3. #3
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    Run. Now. Quick. While you still can.


  4. #4
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    Like the answer and well explained.

    I too noticed GCB were lacking in detail on their website.

    And you are right about changing engineers specs. If he says "A" and you do "B", you have to justify why "B" is acceptable and NOT up to him to prove it isn't

  5. #5
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    Agree about the engineers specs, don't always agree with what they come up with. but its up to me to prove them wrong!

  6. #6
    Old Chippy 6K
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    Quote Originally Posted by jiggy View Post
    Agree about the engineers specs, don't always agree with what they come up with. but its up to me to prove them wrong!
    what lots of DIYers and tradies too is that engineering specs are usually related to systems -ie: how the whole structure will perform when connected or used in the specified way using the components that have been tested and conform. So for example the larger bolts might have the affect given above, but the system might be designed so that any failure is graceful and visible so that bending occurs in a particular component or at a particular place and in a controlled way. Changing one or more components might create unexpected and unwanted results.

    An example can be seen on motor vehicles: that's one of the problems with just placing any old bull/roo bar on a vehicle with airbags - the airbags might still be triggered, but the forces and times will be quite different to the engineered design - and not in any clear way. Likewise a bar mounted without being engineer specced for that vehicle will change the way the body panel collapse occurs - both the rate and direction of the collision force absorption will be different and unpredictable. So when you hit an animal or another vehicle or a fixed object your safety is likely to be impaired not improved.

    Building components are carefully designed for a reason - what appear to be simple and 'commonsense' changes might not be as simple or sensible as they seem. Having said all that there is significant safety factor in most designs so it usually take extreme diversion for specs to make any real difference (and usually from downgrading not upgrading).
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  7. #7
    4K Club Member ringtail's Avatar
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    Without wanting to open this can of worms again, I would like to respond to the op's post. I wasnt going to but I'm bored so bugger it.

    "I thought the tech sheet was self explanatory but may need further investigation."

    The tech sheet specs are only valid for uplift - nowhere does it give or state a live/dead load figure for the stirrup and therefore the argument that the post must bear on the cross brace for adequate load bearing is moot. Unless you are citing a different tech sheet to the installation guide.

    "To clarify, the post support was never designed to have the posts only supported by the bolts as the capacities of the post support bracket itself was too low."

    This makes no sense

    "The post helps keep the sides of the post support rigid. It was found during testing that if the post is not bearing on the cross member, it creates a weak spot on the arms of the post support allowing for buckling and failure of the post support well before the maximum dead load noted on the tech sheet is achieved"

    Mmmmmm. If anything, a weakspot is created at the site of the weld between crossbrace and vertical sections. This junction could fail if the post was to move back and forth sideways repeatedly in a arc of 180 degrees to fatigue the metal sufficiently to break it. Now if that post is one in a series holding a deck up, how can that post, or any of the posts, move in such a manner to allow fatigue to occur ? I'd love to see how pryda have tested this theory in a real world application.

    "When not supporting the post on the cross member Pryda's engineering team found failure well below the maximum capacity noted when bearing the post on the cross member. The failure was potentially low so they insisted on the bearing being used and didn't offer capacities without bearing."

    Failure of what ? the post, the stirrup, the bolts ? Again, how did they come to this conclusion ? Did they put 1 post up in the middle of a paddock with 500 kg sitting on top at 3 metres high, then pulled / pushed back and forth through 180 degrees until the metal broke ? More details please.

    "Going up a size in bolts was an example. Straight away I though of bearer or ledger situations where the size of the ledger is determined by the safety factor either side of the bolt. If the bolt size was increased by the person installing without advising the engineer, there may not be enough timber either side of the bolt and the timber could split."

    Yes you are correct. However, common sense and basic engineering priciples dictate that a ledger in compression will not have holes drilled in the centre of its width but be staggered either side of the centre line ( depending on width) or be biased beneath the centre line giving more timber above the bolt, where it is required. At the risk of upsetting the engineers out there, 10 mm bolts have no place in the construction industy IMO and are generally inadequate for anything other than non structural applications.

    Awaiting you reply hammerthatthumb

  8. #8
    Soldiers Earned Your Right To Free Speech watson's Avatar
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    OK....its time to bring the References into play.
    In case there are different Tech Sheets/Engineering Instructions/ and to ensure we are all talking about the same thing..........please provide a scan or a link to the references you are both using.

    Fair??

  9. #9
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    You know what, Watson? I'm not playing this game. I come here in good faith taking the time to gain the correct information when members of your forum call my place of employment for clarification. I called the manufacturer direct and forwarded this information back to the forum. I also suggested to not take my word for it and to contact the manufacturer direct. With what I'm seeing here I can't continue to direct customers to this site as I had started doing this week.

    It's your forum and you can allow whatever you want. I'm just going to enjoy and learn from other aspects of the forum.

  10. #10
    4K Club Member ringtail's Avatar
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    Fair. In relation to metal fatigue , I am referencing my own knowledge gained through doing a material science course as part of my welding qualifications. A extract from the course notes

    1. Fatigue - alternating stress such as a push / pull motion until the stress reaches a point of failure
    2. Brittleness - member fails without appreciable deformation
    3. ductility - a substance that can be permantly deformed without failure is said to have high ductility ### MS ( mild steel ) has high ductility ------ guess what stirrups are made from
    4. cracking of a weld in mild steel is not common as the carbon content is so low. The higher the carbon content the more brittle the material. As the crossbar is welded ( commonly) on one side only ( sometimes both sides) there has only been a moderate heat input to the parent mild steel. The weld pool will be almost chemically identical to the parent metal and therefore will be very stable and very unlikely to crack. Any crack on a mild steel welded product will nearly always appear in the HAZ ( heat effected zone) caused by the weld. This is generally at the toe of the weld or within 2-3 mm from the weld.
    Any metalurgy book / google search will confirm this information, but in short, mild steel is used because it is so forgiving ( ductile , because it is only .25 % carbon) and will yield a lot before failing.

    Timber

    I reference AS1684.2, section 2.3 and figure 2.8 for vertical nail lamination where two timbers are to be joined. This is the only info I can find as there is no reference to ledger beams. It should be noted that the AS is the minimum standard. I also reference AS1684.2 section 4.1.6, notches, cuts and holes in beams, bearers, joists and rafters. Note figure 4.1 ( f and g ) where a beam is less than 200 mm in depth ( which would apply to a ledger) if the hole is in the centre of the beam, only 1 hole per 1800 mm is allowed ( g) if the hole is staggered, 3 holes per 1800 ( or 600 ctrs) is allowed
    Attached Files Attached Files

  11. #11

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    Default A word From The Admin Team

    HERE'S THE WORD

    WE IN THE ADMINISTRATION TEAM ARE NOT
    ENGINEER'S
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    STRUCTURAL DESIGNERS

    OUR JOB IS TO KEEP THESE FORUMS RUNNING SMOOTHLY

    HENCE

    WE RECOMMEND THAT YOU CHECK THE FOLLOWING

    PRODUCT TECHNICAL DATA
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    THE THREAD IS CLOSED


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