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Cut and weld stirrups, pack out or bolt on bearers above plate for correct height?

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  1. #1
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    Default Cut and weld stirrups, pack out or bolt on bearers above plate for correct height?

    I’m building a deck this weekend over a cement slab. The cement slab isn’t level (i.e. its quite slopped away from the house) and is raised at one end where a section was replaced some time ago. Rather then making holes in the cement for the stirrups to be cemented in, I’m going to bolt stirrups directly to the cement. The only problem is that because the cement isn’t level and I want the deck (bearers) to be level, I obviously can’t get stirrups in the different lengths (heights) I require (they are all short, at less than 300mm).

    I have 2 options; firstly I can cut the stirrups and weld them at the height required. Alternatively, I can bolt the stirrups down and pack the top plate where the bearere would normally rest with a piece or 2 of thin timber (between the stirrup plate and the bearer resting on it), or can I just bolt the bearer to the stirrup with a few cm of clearance between the stirrup plate and the bearer? Does the bearer need to be resting on the plate or is it ok for the bolts to be taking the weight?

  2. #2
    Senior Member brynk's Avatar
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    another alternative would be to chemically set threaded bolts into your concrete slab. now, pack under the stirrup to the right height & plumb, then bolt the stirrup down onto the packer. this will save you a bit of grief!

    have a read of this older thread for a discussion on the merits of chemset/dyna's (also another option!) & a method of installing the chemical anchors if you are not familiar with them. http://www.woodworkforums.com/showth...set#post671307

    r's brynk
    "Man got the opposable thumb - woman got four opposable fingers." - Rowdy

  3. #3
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    I dont like the sound of packing out the top of the stirrups to hold the bearer of the stirrup plate; any ideas is this a good or bad idea? Likewise not packing it out and bolting the bearer off the stirrup plate?

  4. #4
    Senior Member brynk's Avatar
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    if you bolt the stirrup flush to the slope it will be out of plumb. if you don't rest the bearer on the stirrup you would need to up the # of bolts to ensure strength is maintained. you are also changing the geometry of the stirrup because the load is no longer a direct path to the base-plate, you are introducing a rotational force even at rest - if you look at the stirrup closely you can see the top-angle where you bolt the bearer is generally tack-welded to the post, likewise to the base-plate. these are designed to be vertical.

    with my method suggested you will be packing under the stirrup's base-plate with steel / similar non-compressible material, not under the bearer. then using concrete anchors, be they chemical or friction, to hold the stirrup down onto the packing & the conc itself. the stirrup will be plumb. i should also mention then you need to mix up a little mortar and stuff it under the stirrup base-plates to seal off the packers from exposure to the weather/poinding, etcet.

    another alternative to packers under the base-plate is to use two nuts on the threaded chemical anchor - one on the bottom side to rest the plate on and one on the top side to lock it into place. if you use this method then you should use a little loc-tite on the nuts or nylock nuts, and encase the whole base-plate of the stirrup, threaded rods and nuts in mortar to prevent weathering or loosening of the nuts.

    these are all acceptable methods of construction used mainly in industrial / commercial rigid steel framing. most light-posts are set into the ground this way, though the threaded rod that they are bolted to is usually cast into the concrete footing rather than being drilled in at a later date - this is to give more strength to resist rotational forces at the base.

    r's brynk
    Last edited by brynk; 18th Apr 2008 at 01:11 PM. Reason: more detail
    "Man got the opposable thumb - woman got four opposable fingers." - Rowdy

  5. #5
    Senior Member brynk's Avatar
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    here in this photo you see the threaded rod is suspended inside the concrete's reinforcement before the pour. a light-post is bolted after the pour to these bolts, which will protrude from the surface.

    in your instance, you are inserting the threaded rods after the concrete has cured. um, your concrete is also not level - but a picture says a thousand words
    Attached Thumbnails Attached Thumbnails bolts-after-pour.jpg   rag-bolts.jpg  
    "Man got the opposable thumb - woman got four opposable fingers." - Rowdy

  6. #6
    Rigid Member UteMad's Avatar
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    Bolt the stirrups to the concrete.. you'll find different brands have slightly different lenghts like some are 220mm others 200mm etc ... we just buy a box load of mixed and find the one we need and pack the base accordingly or cut 10mm out of the bot of the bearer to go down...
    Just a fiddle we have done ones like this where one end has no bearer and the other is 300mm up to the bearer.. you may have to change your sub structure design to suit the section your covering

    look at the bolts as positioning and uplift only and you wont get into trouble

    good luck

    cheers utemad


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