Piers - one pour with form work or slab and fixed metal pier?

[mura_gadi (Steve)]

Hello,

I watched the sky and telescope YT on pier pours etc and they state that the pour and the pier are two items.

The fixing of the pier to the slab is bolted down under high load. The idea being that the high load tension reduces the vibrations. The key loading stone stated was 1mx1mx1m, which is a fairly solid anchor!.

I was wondering if you had tried this pour and system before and the single pour with form work and noticed a difference in performance between the two options?

Both can be secured under tension, but the form work places the tension at the top of the beam and not on the loading stone.


Thanks

[strongmanmike (Michael)]

Sorry I'm not quite understanding exactly what you are saying/asking here Steve ..?

Mike

[mura_gadi (Steve)]

Ah, someone wants the English...

[strongmanmike (Michael)]

Ok ok...I think I may understand your query

I think you wanna know if THIS (NB: the pier was sitting up on nuts in this photo but was eventually bolted flat to the concrete footing) is any better or worse than THIS...? (bearing in mind that I had the same black steel pier bolted to the top of this monolithic pillar+footing too) aaand also HERE and again, same black steel pier....an almost 20 year journey and 4 observatories

If so, then the (very scientific) answer, is... all were bloody rock steady the last approach was probably the least stable and did show some very minor vibrations because I did not pour that pillar onto a wider, larger, heavier footing base but instead just continued the concrete pillar into the ground at the same diameter, with about 1m under ground and 1.3m above ground, so I suspect there was perhaps just a little bit of a flag pole effect..?

Mike

[appiice (Ed)]

Hello Steve

I think your question is moot, the size of the pier you mentioned ( 1 x 1 x1 ) would have a weight of about 2.5 tonnes, if the mount was attached so there was no slop in the connection I doubt it would matter how it was poured, for example, my mount is sitting on a 1000mm long 250 dia' steel tube with full length welded gussets, this rests on a .8 x.8 x .8 concrete base which is a projection above a concrete mass of 1.5 x 1.5 x 1.2 ( into the ground ) the two concrete masses total just over 8 tonnes, all the steel reinforcing is 16mm deformed bar, the connections ( 8 x 16mm bolts ) between the steel pier and the concrete base are NOT torqued down but are tight.
Nothing moves - of course 8 tones of concrete may have something to do with that but I think we over think problems which may not be there in the first place.

Why did I build such a big mass pier? I wasn't going to dig a 1 x 1 x1 hole by hand, it didn't cost much more to dig a slightly bigger hole, my observatory needed the height and small amounts of ready mixed concrete carry a price loading, so 3.2m in a big truck was not a lot more than 1m in a small truck.

Ed