Quote:
Originally Posted by Jeffkop
Al .. The floor will be about 400mm - 500mm above the ground and so to the top of the footing.
|
That's not a problem with your floor over the footing (and separated from it)
.
Quote:
Originally Posted by Jeffkop
I planned to bolt the pier onto threaded rods that were into the footing. Do you think I should be putting the pier into the footing ???
The floor of the Obs will not be in contact with the pier
|
For rigidity the preferred options in decreasing order of rigidity of the pier footing connection are:
- Embed the pier in the footing
- Adequately grout the pier to the footing
- Bolt it securely to a smooth, flat footing (with a thick, stubby base plate (distance of bolt from pier member / thickness of baseplate <=2!)
- Bolt it to an uneven footing
- Bolt it on levelling nuts on the hold down bolts (but no grout)
- Bolt it down on a central packer only (no grout)
A well grouted connection is near as makes no difference as good as embedding the pier, and it's easier to do a neat job and get it plumb.
The "right way" to apply the grout is set you pier up level and plumb on the anchor bolts with levelling nuts underneath, then use a good quality non-shrink grout to fill underneath. If your grout is stiff push it in from one side until it comes out the opposite side so you know the joint is full. If you are using a free flowing grout (epoxy etc) then form up for the grout and pour it in from the one side to make sure there are no bubbles in the joint.
Now if you are a bit lazy like me and think you can do it...
... (WARNING! There's potential for this to go wrong so attempt this at your own risk!
)
What I did with mine was cast my footing about 20mm lower than floor level. I then made a
stiff mortar mix and levelled and smoothed that off to floor level. While it was wet I placed the pier on it and used the anchor nuts to pull the pier down just
slightly into the mortar (just enough to make sure there's no air bubbles - not enough to deform the mortar around the baseplate) and adjust the nuts till the pier is plumb and level. Then leave it to cure and make sure is protected from anything that could bump or move it while the mortar sets. After a week of curing tension the anchor nuts up tight
. I used a tension wrench to set mine just because I could
. Avoid tightening the anchor nuts too soon so you don't crush the fresh mortar/grout.
... and Robert is your mother's brother...
Quote:
Originally Posted by Ian Robinson
Interesting that you guys advocate supermassive footings for piers (ie 1.5m x 1.5m x 1.5m presumeably only maybe 300mm above ground level).
Is there a good engineering reason for this ? and does this depend on the type of gound you have ?
I have seen similar recommendation by guys at CN, BUT there they have the issue of the ground freezing in winter - and it's done because of this annual freezing and thawing. Obviously not a problem here unless you live above the snow line (in the Snowy Mountains). So is it really necessary to have such massive (AND DEEP) footings ?
|
I could see the need for a wide footing in sandy soil perhaps where there's simply no chance of getting anything too solid, but in reality depth is what you need. The ground pressure increases linearly with depth, so the deeper you go the more secure it is... unless you find rock
.
Active clays soils will always be a problem with movement unless you can get to bedrock
. In that case, you might have to live (hopefully) with regular polar alignments to correct the movements
).
Al.