Advice on building a pier

[E_ri_k]

Hey guys, I have just acquired a new mount head, and I need to build a pier in my obs. Just after some general suggestions from those who have done this.

Best ways of fixing the pier to the foundation?
Minimum dimension of the hole in the ground?
Re-enforce the concrete?

Thanks :)
Erik

[traveller]

Hi Erik,
There are several threads on piers under DIY observatory thread. My pier is a light weight one so I only dug a footing of 450x450x600 mm deep footing (12 bags of 20kg pre mix concrete, don't use the quick set type, use the normal type) and I cast threaded rods into the footing.
Have a trawl through the DIY obs thread and. It should answer most of your questions.
Best of luck.
Bo

[E_ri_k]

Thanks Bo.
Erik

[gregbradley]

I have a few piers and a slab. The pier was about 800mm deep and around 800mm square with a 100mm flange at the top. I filled it with a lot of steel reo bars and concreted it.

I then got a very heavy steel pier from Pegasus and its bolted to the pier with a series of anchor bolts. I packed underneath the pier with cement.

Its very stable.

Some have bolts set into the concrete but in my case the pier came later so I used anchor bolts. Big ones.

At my remote site I simply dug a hole about 600mm deep a bit bigger than the 8 inch diameter steel tube then filled around and in it with rapid set concrete. Worked like a charm.

Greg.

[g__day]

Some suggestions:

I for your base plate that attaches to the ground, work out where you want your holes to be - then drill through a wood back plate - so you have a light wooden plate you can use when setting bolts into your slab.

When you make your pier use per-galavinised steel. Go for the largest diameter pier you think functional to add stability.

Add gussets - a bit bigger than you think you need it to stabilise the pier.

When you well the pier column to the base - the heat may warp the base - so consider maybe spot welding in a few places, rather than say starting at one point in the column and working your way around the circular base of the column.

For the hear of the column you can either use a flat plate wielded on and then another plate bolted with four large plates on top of this - so you can level it - or make an aluminum cylinder that just fits into the top of your pier and bolt a slightly over-sized stainless steel slim disc on top of this; then you machine in the well where the base of the mount fits, then slide this into the top of your pier and bolt it in. I did the later approach - looks really good, no sway or movement whatsoever, your can't fine tune your mount level - but it doesn't need to be perfect. Once you drift align well it doesn't matter how exactly level your mount is.

[E_ri_k]

Thanks for the advice guys. I have started digging a hole, will be 1 cubic metre. I have gotten down 600mm and hit clay, so I think it will be pretty solid. I have spoken to a local metal fabricator, who has done some worker me in the past.

I'll get him to make the pier for me, and then thinking maybe a cage with bolts set in the right positions. Sit it in the hole and fill it.

I have seen some piers with a second plate mounted onto the main flange, with bolts in each corner for fine tuning the level.

Erik