Pinning cedar fence posts to ledge

[roricka]

On coastal Maine, I'm having an experienced friend install a white cedar picket fence. 8' sections, 6' and 8' high. Some of the 8" cedar posts will be sitting on granite ledge (bedrock).  What is the proper method for pinning these to the ledge? Is the technique any different if the ledge is a foot or two down, compared to being on the surface?

Thank you.
Tony

[flyingvan]

  When I get home again I can get a picture of how I worked around this, I'll be very interested in other solutions.  I drilled into the rock with a hammer drill and epoxied rebar in, then made a form out of a bucket cut in half and inverted the top half over the rebar.  Filled it with concrete that was colored to match the rock then sunk a Simpson CBSQ in the concrete.  I suppose if the ledge had some soil over it I'd use the whole length of the bucket, or a sonotube, or the soil itself

[pocono_couple]

wow.. can't help with ideas for anchoring the posts..   but curious about where you are in Maine.    We recently bought a piece of property in  Phippsburg, and I can't wait to get started on a project up there.. but  I have enough on my plate right here in PA  for a while    jt

[UK4X4]

https://www.permacolumn.com/drill-set-models

if your rock is close to surface scrape away, drill and attach the brackets

[roricka]

Thanks for all the help. Btw, I was wrong -- they're 5" posts, not 8". We're in Portland. Great little city.

[pocono_couple]

I agree - love Portland - tried to convince my step daughter to go to southern maine community college so that we could visit her there

[DaveOrr]

I'm using these: http://www.strongtie.com/products/connectors/canada/rcps.html  to pin my foundation posts to the bed rock on my property. 

[flyingvan]

5" posts?

[Don_P]

A note from the Simpson catalog,
"Post bases do not provide adequate resistance to prevent members from rotating about the base and therefore are not recommended for non top supported installations (such as fences or unbraced carports)". This also applies to unbraced cabin posts. These post bases are really intended to give uplift resistance.

The perma column bases do provide some moment resistance but not a whole lot. I can't remember exact numbers but a fencepost is an easy way to describe moment resistance. I think I remember one of them giving 500 inch-lbs moment resistance.
Divide by 12 = 42 ft-lbs moment resistance.
If the fence is 1' tall divide 42 ft lbs by 1' = 42 lbs resistance at the top of the post.
If the fence is 6' tall divide 42 ft lbs by 6' = 7 lbs resistance at the top of the post.
Short of boring a substantial hole into the rock and using a pipe cantilevered out of the rock for a post, bracing is the easiest way to pick up real overturning resistance.

[Adam Roby]

I meant for this to go here, might also apply to the other thread.

I wonder if you could use a combination of different braces to accomplish the whole task.  For instance, use the carport saddles for the uplift counter-effect, and use some braces on the sides of the posts to counter the rotational forces.




I couldn't find taller braces (brackets) but imagine them being as high as the saddles would be, two of them coupled with the saddles should provide at least some additional support (I would imagine).

* Ooops... this was meant for the other thread...