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I am currently undertaking an extension to my house, a double garage with a couple of rooms above.
I have poured the slab and note that the engineer has specified a threaded rod in both front corners from the top plate right down into the slab (I would have to chemical it in) - this would be a length of rod about 6 metres long
Is this really necessary? Wouldn't hoop iron secured through 8 or 10 courses of the piers be sufficient?
Any thoughts
Mac
If that's what the engineer has specified then that's what you'll have to fit. I doubt that hoop iron as you're proposing to fit it will be acceptable because it won't provide a continuous tie down from roof to footings. You can just chemset a stud in and then use a pump rod connector to attach the longer length. Generally you cast a short length into the slab, usually hooked under a perimeter bar.
Mick
If you want to alter what the engineer specified you must get them to respecify the alternative, otherwise they will not take responsibility for the job should any thing unforseen happen.
Theraded rod is available in 1 & 3 mtr lenghts, they can be joined with a coupling. M10 or M12 rod is not all that expensive and is available most places that sell fasteners or building supplies.
If there is nothing specified as to how to fix the rod to the slab you may want to consider a mechanical anchor, the quickest and simplest is called a Pipe Spike, drill a 6.5 or 7mm hole (depending on the hardness of the slab) and hit it in with a 2lb club hammer.
http://www.powers.com.au/products/focus.aspx?bgid=82
And another is the Snake Drop in, drill a hole and screw it in with an inhex driver.
http://www.powers.com.au/products/focus.aspx?bgid=24
or this one.
http://www.powers.com.au/products/focus.aspx?bgid=29
All of these require no special setting tools and will take the loads you need, but you may want to run that past the engineer too. Be careful not to be too close to the edge of the slab as load reductions apply, even to chemical anchors.
The threaded rod would give a certain tie down which must be required. If you want to change it you need to ask the engineer. Also, I would verify the method for the connection of the end of the rod into the slab as it sounds by your description that the rod was meant to be cast in.