reinforcing for pier cube

[Spookyer (Brett)]

Hi all, got my pier holes dug, about 1.1 cubic meters each. I may have an opportunity to get a pour done in the next week when they do the house slab.

Is it necessary or advisable to put some reinforcing in the concrete? If so how much?

[jenchris (Jennifer)]

A couple of layers of f8 200 won't hurt,
But it's moot as there's very little tensile strength required.
It will at least give you something to hitch the j bolts to

[AlexN]

Mate. I'm a concrete batcher. Have been for quite a few years now. If you want a kilo or two or concrete reinforcing fibres let me know.

[JoelyE95 (Joel)]

Brett,

I'd second Alex's comment.

If you are not casting in a hold down plate, and are just dynabolting a peir, there is no need to stuff around fixing steel into place, you should just get the fibres added to your batch. Hymix and Hanson can help you out there.

If you are casting in a hold down plate, I would add at least a layer of top mesh (F72 or F82 at about 900m square) with about 40mm cover. Just jiggle it in when the concrete is added. Make sure the plate is level though, before you walk away to appreciate your work.

Joel

[AlexN]

Are you mixing this concrete yourself or ordering a load in an agitator? Again, I get staff rates at boral and can add fibres to your load that will increase the torsional strength no end.

[Spookyer (Brett)]

I plan on getting it done when they do the house slab so I don't think they will mix me anything special, it will just be the same mix as for the house slab.

Where is the best place to get two square meters of reinforcing?

I guess the fibres have to go into the mix so they are probably out.

Brett

[AlexN]

Yep fibres need to go in the mix. I can supply fibres to you to add to the mix before its poured into the hole. Failing that. For 1 square meter of reo I would go to Caboolture concrete supplies.

[Pierman (Phil)]

Hi mate, good choice to go the fibres for the concrete footing. I am not sure how much you might know about the finishing of the footing but may I offer a couple of suggestions to help you get a good long term outcome.

Insulate the pier footing from your surrounding observatory slab or flooris a given.

I would strongly encourage you to think about securing your pier flat to the concrete footing and not suspended off the footing on the four or six threaded bolts.

From a purely scientific and practical perspective, It is no use going for a good heavy duty steel pier to gain that rigidity and structural integrity if you then destroy all of that by mounting it all on four threaded bolts.

If mounting to the concrete it might be worthwhile doing some work in the forming up and levelling the top of the foundation the pier is going to sit on as perfectly as possible so that when you do place the pier, you start with a level foundation that you can secure your pier to with confidence.

Level bottom = level top.

Hope this helps you and good luck.
Cheers
Phil
Pegasus Piers

akubrahatman@gmail.com

[Spookyer (Brett)]

I imagine the concrete will be already mixed and in the truck for the slab so I don't think I will be able to add fibres for my 2 cubic meters.

The floor of the obs itself is elevated off the ground, the pier is getting bolted into the concrete block in the ground directly and will come up through a hole in the floor of the obs. Not ratcages at the top or bottom.

I have built wooden formwork in an attempt to get the top of the concrete block level but will have to supervise this on the day to get it level and flat and smooth so the bottom plate of the pier will sit on it nice and flat and as level as possible.

I am currently getting a quote for the pier construction.

thanks for the advice.

[rally]

Brett,

To get the pier bedded on the footing -
Without having to get the slab perfectly level - which can be very hard if you have set the mounting bolts into the slab at the time you pour.
ie the mounting bolts can be attached to a simple metal frame that gets set into the concrete at the time of pouring.

The other way is to drill holes and use chemset or similar to glue in threaded rod, or use standard masonry anchors.

Just make up a small amount of slurry level and spread that flat and evenly over the footing the moment before you tighten up the bolts/nuts.
Get the pier level, tighten nuts firmly but not to full tension, allow the slurry to cure and and then tighten the bolts to full tension.

Or you can get expanding concrete used for this specific purpose - set the pier onto the bolts/threaded rod protruding form the pier footing, using jacking nuts under the pier mounting plate and adjust them until the plat eis level, tighten the hold down nuts on top and then ram and pack the expanding concrete under the pier.
It can be done without expansing concrete too !
For a pier it will be fine.

The slurry is in compression so you dont really need that much to be effective, just shove it in until no more can be pushed in without some coming out the side and smooth off the sides at 45 degrees.