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Vertical tie downs through wooden bearers

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  1. #1
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    Default Vertical tie downs through wooden bearers

    Hello Folks

    Just after some advice regarding tie downs.

    AS1684 specifies M12 rods to tie down bracing walls. So length of M12 with 50mm washer top
    and bottom, m12 nut top and bottom and the rod straight down from top plate to bearer through a drilled
    series of vertical holes through the frame and the drilled vertical hole through the bearer. Is this correct,
    or should I have a thick piece of angle bolted to the bearer to house the M12 rod?

    Similar setup regarding the bottom plate tie down. Do I just screw/bolt down through the bottom plate
    and through the joist/bearer or again use a piece of angle on the side for fixing?

    The angle would have to be rated of course but I would think it would be susceptible to bending.
    The hole straight down the bearer seems the strongest. Also as the bearers are laminated, would
    this impact its hold down ability or compromise the structure.

    Any help please.

  2. #2
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    Default Vertical tie downs through wooden bearers

    Do you have a bracing plan or tie down detail you can share for exactly what your doing?

    I know you can buy screw bolts with threaded heads to accept 12mm rod for situations like this.

    If you have a project on the go, the exact tie down would be specified so you have to follow exactly what it says. I don’t think an angle would pass.


    ====

  3. #3
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    Hi Micky

    I am building a backyard studio. I had design plans drawn for council submission but no construction plans. It is basically four walls and a roof, as a bit of a project I am doing it all myself
    (apart from the footings, roof trusses, plumbing, electrical, waterproofing and tiling) by working through 1684.2. It is woefully over-engineered as I want it to last forever. Anyway, AS1684 calls for M12 rods
    either side of a short section of bracing wall (of which I have designated 2 to the resistance calc's) but doesn't really specify how to fix the bottom end of the rods to the subfloor. That's
    why I posed the question of straight down through the laminated bearer. It is a sheet roof in N2 area so specific fixings required for bottom plate to subfloor. Type 17 14g batten screws
    are acceptable ( I was planning on every joist , again over engineered I know) but do I just screw them straight down with the required 'bite' into the joist. Detail is a bit lacking in the standard.
    I suppose if you are in the building industry you get taught/shown these things but it's just me and I don't have any contacts in the industry. Any help much appreciated.

    On a different note (probably need a new thread) I am using LevelMaster piers. The underside of the bearers are only 450mm off the ground. The actual length of SHS coming out of the concrete footing to the pier
    head is about 200mm. Because its 'elevated" I must address subfloor bracing under 1684 but there's not much room on the SHS to fix the bracing. I think I read somewhere that under 600mm bracing not required
    but I cant find a reference. Can you enlighten me.

    Thanks.

  4. #4
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    Default Vertical tie downs through wooden bearers

    Quote Originally Posted by Brett67 View Post
    Hi Micky

    I am building a backyard studio. I had design plans drawn for council submission but no construction plans. It is basically four walls and a roof, as a bit of a project I am doing it all myself
    (apart from the footings, roof trusses, plumbing, electrical, waterproofing and tiling) by working through 1684.2. It is woefully over-engineered as I want it to last forever. Anyway, AS1684 calls for M12 rods
    either side of a short section of bracing wall (of which I have designated 2 to the resistance calc's) but doesn't really specify how to fix the bottom end of the rods to the subfloor. That's
    why I posed the question of straight down through the laminated bearer. It is a sheet roof in N2 area so specific fixings required for bottom plate to subfloor. Type 17 14g batten screws
    are acceptable ( I was planning on every joist , again over engineered I know) but do I just screw them straight down with the required 'bite' into the joist. Detail is a bit lacking in the standard.
    I suppose if you are in the building industry you get taught/shown these things but it's just me and I don't have any contacts in the industry. Any help much appreciated.

    On a different note (probably need a new thread) I am using LevelMaster piers. The underside of the bearers are only 450mm off the ground. The actual length of SHS coming out of the concrete footing to the pier
    head is about 200mm. Because its 'elevated" I must address subfloor bracing under 1684 but there's not much room on the SHS to fix the bracing. I think I read somewhere that under 600mm bracing not required
    but I cant find a reference. Can you enlighten me.

    Thanks.
    So I’m assuming you have a bracing rating specified and that corresponds to the table which requires you to use m12 rod - only because there are other options which don’t require it.

    I would assume you would need to go through the bearer in that case.

    I haven’t done any frames on posts and bearers but I imagine the tie down would be similar to a second storey - strapped and 2 bugle screws at min 1200 and at lintel/bracing points(n2). Set them just below the plate surface. If you look in the standard it’s the same spacing and positioning principles as a masonry anchor.


    I do find it odd that you don’t have a framing plan that specifies exactly how it is all to be braced and tied down - that would be required by council surely.

    ====

  5. #5
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    Default

    The AS also provides other options such as strapping of the required studs at top and bottom plates. I've always seen using M12 rods a waste of money when you already have the studs in place, and their connection just needs strapping for them to perform tie down per the AS. Then you also strap the bottom plate to the bearer near the stud straps.

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