Foundations for Large Sign
Foundations for Large Sign
(OP)
Hi guys
I have a large sign (15m x 4m or 50' x 12') that is situated on 8m (24') of sandy clay which overlies weathered rock. I need to come up with the best foundation system to resist the large overturning moment.
I have decided on using either a very large pad footing (several cubic meters of concrete required to provide the required resistance to overturning). Or provide a pile cap with either 2 or 4 piles that go down to rock.
Are there any other foundation systems that others would like to recommend to resist such a large overturning moment as this one.
I have a large sign (15m x 4m or 50' x 12') that is situated on 8m (24') of sandy clay which overlies weathered rock. I need to come up with the best foundation system to resist the large overturning moment.
I have decided on using either a very large pad footing (several cubic meters of concrete required to provide the required resistance to overturning). Or provide a pile cap with either 2 or 4 piles that go down to rock.
Are there any other foundation systems that others would like to recommend to resist such a large overturning moment as this one.






RE: Foundations for Large Sign
Or you tell me P and M. My gut feeling is going with single pile.
Sign Column mounted on pile top and piles extends to rock below.
Make sure to extend pile 12" above grade.
RE: Foundations for Large Sign
RE: Foundations for Large Sign
DaveAtkins
RE: Foundations for Large Sign
RE: Foundations for Large Sign
RE: Foundations for Large Sign
Pads are straight forward and can be done by any ground contractor. Usually only 4 foot deep.
I doubt a caisson would work in this instance due to the short embedment in the clay down to the rock. The rock wont stop this rotating in the clay and you dont want to bore 15' into the rock.
For piled foundations I usually would use helical piles, but once again I dont think it would work in this case.
If you were to use piles I would suggest raked traditional H piles. But I would think this would be overkill.
RE: Foundations for Large Sign
Takes no specialized equipment, just dig a hole and fill with concrete (a lot of tconcrete).
Sometimes mobilizing a cassion or pile rig is more expensive than just pouring concrete.
RE: Foundations for Large Sign
the dead load of the sign is 5tonne and the overturning momenet is around 800kN m for a 1000yr wind event. As you can see, it is a very large overturning moment and requires a lot of concrete to resist overturning.
RE: Foundations for Large Sign
RE: Foundations for Large Sign
Mike McCann
MMC Engineering
RE: Foundations for Large Sign
Is this a cantilever sign? If so, torsional forces can be quite large (esp. given the 7.5m+ moment arm).
For this size panel, I'd think a 6ft (3m) caisson would do nicely.
Also note, design is just one leg of the triad. Materials and installation are just as important as your design... If this is atypical construction for your area, bump up the safety factors to account for poor workmanship.
Good luck on your project! RAF
RE: Foundations for Large Sign
RE: Foundations for Large Sign
RE: Foundations for Large Sign
As RAF noted, your torsion component on this will likely be large.
RE: Foundations for Large Sign
RE: Foundations for Large Sign
RE: Foundations for Large Sign
RE: Foundations for Large Sign
Pole extended to the bottom of foundation could get away without structural reinforcing. I would provide minimum steel on the upper few feet of the footing, maybe down to local frost level.
RE: Foundations for Large Sign
I think you mean the same as what we almost always did. Extend the pole into concrete pier almost to the bottom without any rebar. The whole foundation with pole functions to resist the lateral and you don't have to mess with a big base plate.
RE: Foundations for Large Sign
You pozzled me on "base plate", did I mention it? Maybe you were trying to point out my previous "T shape foundation" suggestion, which was intended to overcome excessive OT while utilzing both soil pressures around the shaft, and bearing pressure under the cap. Or you were questioning "I would provide minimum steel on the upper few feet of the footing, maybe down to local frost level." in my latest response, the footing here was meant the "drilled hole" as mentioned by cmm1080. So which one is your question pointing to?
RE: Foundations for Large Sign
RE: Foundations for Large Sign
1000 year return interval?
RE: Foundations for Large Sign
RE: Foundations for Large Sign
RE: Foundations for Large Sign
I would then go with a 5x5m pad footing with 4 helical (screw) piles each side 7m into the sand. Load on the piles is approx 50kN plus or minus the pad which will give you the minimum size anchor.
If the load tsts on these dont get what you expect then you can always add another one.
I would imagine that where you are, a 2m caisson or bored pier would be uncommon and expensive.
RE: Foundations for Large Sign
The Australian codes don't factor the wind loads. The appropriate return interval is selected according to structure type (eg farm shed or nuclear facility etc) and limit state (serviceability or strength/stability).
I would have used a 500 year return interval for a sign.
RE: Foundations for Large Sign
RE: Foundations for Large Sign