Attaching post to concrete

[gsouth]

All,
A few days ago I posted a topic about putting a deck pier into back filled soil. The general concensus of everyone I have spoken to is not to do it - either dig till I hit natural ground, or build a concrete pad to support a pier.

A friend has suggested an alternative and I wanted to see what you think.

Attachment 17596


The idea would be to attach the post to the decking of the pool, which is 150mm thick steel reinforced concrete. The post would be supported by a bracket which would be attached to the concrete.
The engineering plans for the deck state that it's engineered to take a 2kpa live load - would this be sufficient to do the above?
I can't put the pist on top of the deck as there isn't enough room.

Thanks
Geoff

[rrich]

Geoff,
Why would you put stress on the side of the pool to save a few dollars by not pouring the propper concrete foundation for your deck supports? All of the concrete deck foundations would cost less than repairing a fracture in the pool decking or the pool itself.

[bennylaird]

Pretty sure you would get no where near 2kpa load in that configuration, just heartache from the damage caused when it breaks off and destroys your pool foundation. Go with a pad and a stirrup as well to keep the post from rotting once it gets wet.

[gsouth]

Guys,
Thans for the responses - the reason I'm doing it this way is because the soil here is all backfill, and to reach natural ground would mean sinking a pier of over 2 metres deep.
The sewer line runs adjacent to this area, so pouring a pad bigger than 400x400 would mean the pad sits on top of the sewer.....

This was one alternative....

Geoff

[bennylaird]

Might be a use for an engineer here then, they have their uses at times.

[Eastie]

If the post were extended and concreted about 400-500mm into the soil (still using the bracket to attach to the slab) the load applied to the rail would put the force against the concrete in more of a compressive load rather than causing strain on the lip - much less likely to cause a problem.

[jimc]

out of left field, why not specify a larger bearer and just avoid the fill area.
Alternatively if you where to sink a 200x100 redgum/concrete sleeper into the surface then drop your stump directly in the middle of the sleeper, it would take the compressive load and disributing it over a large area.
only hiccup with this suggestion is if you are planning on getting it inspected.

I have jsut installed a 2000l water tank on backfill utilising the sleeper method with no movement in the surrounding soil!

[rod1949]

I think you a worried about nothing. You state is engineered for 2kpa live load. What’s that, 2 tonne?
Are you ever going to get 2 tonne, be it people or whatever, immediately above that post? I don't think so.

[silentC]

out of left field, why not specify a larger bearer and just avoid the fill area.

I suggested that in the last thread. Seems like the simple solution to me.

[bennylaird]

I think you a worried about nothing. You state is engineered for 2kpa live load. What’s that, 2 tonne?
Are you ever going to get 2 tonne, be it people or whatever, immediately above that post? I don't think so.

If atttached to the side then the load would be expansive, doesn't concrete dislike an expansive load?

[rod1949]

If atttached to the side then the load would be expansive, doesn't concrete dislike an expansive load?

Yep you are probably right. I omitted to say that I wouldn't fix it to the concrete pool surround as water from the pool with all its chemicals in will very quickly corrode the post (if steel) and the fasteners. I'd dig a hole in the ground.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
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[gsouth]

All,

Thanks for the advice so far in both threads.
I have attached a pic of what I am trying to do.

Attachment 17608


The decking boards will run from top of picture to bottom of picture to match the existing deck.
The addidtion deck is 1300 wide from the house.

As you can see the area where the 'problem' post is going to be is right where the fill is, hence trying to figure out the best way to get around this.
What's not on this picture is the sewer which runs about 400mm to the right of the pool running from the top of the picture down and under the house.

The length of the 2 bearers drawn is about 3300.

If I was to put a post in before the fill area, how can I calculate the size needed to cantilever out to the end? Is this even recommended? The cantilever would be about 1800mm to where I could put a post on natural ground.


This is my first deck, so I am struggling through this part of the design and appreciate all the help.

Cheers
Geoff

[johnc]

Digging is generally not all that tough in disturbed ground, why not just get yourself a post hole digger. Not sure how deep the motorised ones go these days, but there are hand units that will almost get there and if you are really lucky you might get to solid ground before then. If the going gets tough just fill any holes with water and leave overnight, that will usually soften the fill a reasonable distance in.

Besides a bit of shovelling is good for the soul, but only because it resembles penance .
John.

[bitingmidge]

[COLOR=black]Are you ever going to get 2 tonne, be it people or whatever, immediately above that post? I don't think so.

Are you going to put a load on the pool coping that it wasn't designed for?

Yep.

Is it going to be cheaper to do it properly now than to fix the crack at the edge of the pool in five years time?

Yep.

The two metres isn't a big deal, go to your local hire joint and hire a hand auger (post hole digger) with a couple of extensions. You should be able to bore a six or 8" pier by hand in no more than 15 minutes.

If you've only got a 6" auger, drill two or three piers into the solid ground, fill with concrete to the level of the underside of your normal footing, then build the column normally.

It's really no big deal.

Cheers,

P (Do it once, do it right.)