Sign foundation
Sign foundation
(OP)
Hi all,
I have an existing caisson supporting a sign post where the top of the caisson is below the sidewalk. The sign will be removed and the caisson will be re-used to support the new sign. I want to place the new sign base plate above the sidewalk surface (with a protection box) to allow inspection of the anchor rods and base plate in the future, and so I will need to extend the top of the caisson so that it projects 6” above the sidewalk. The diameter of the existing caisson is unknown but will be confirmed during construction, it is likely minimum 16” in diameter.
Several questions:
1. I am having a hard time getting the new post-installed anchors to meet current code requirements for combined tension and shear given a 16” diameter caisson. Sign base plate anchors will be threaded rods that will be embedded using Hilti’s HY200 adhesive system. I am using Hilti PROFIS to design the anchorage, and increasing the embedment beyond 8" does little to increase tension and shear breakout capacity. Any ideas for an alternative solution? Mechanical anchors (undercut anchors) offer greater capacity but they are not long enough to anchor into the original caisson from the new raised top.
2. The new caisson extension will be reinforced with 6 bars in the perimeter. Do these need to dowel into the original caisson even if the new base plate anchors anchor directly to the existing caisson? If so, would this be a nominal embedment of say 4”?
Yours thoughts on this would be appreciated.
I have an existing caisson supporting a sign post where the top of the caisson is below the sidewalk. The sign will be removed and the caisson will be re-used to support the new sign. I want to place the new sign base plate above the sidewalk surface (with a protection box) to allow inspection of the anchor rods and base plate in the future, and so I will need to extend the top of the caisson so that it projects 6” above the sidewalk. The diameter of the existing caisson is unknown but will be confirmed during construction, it is likely minimum 16” in diameter.
Several questions:
1. I am having a hard time getting the new post-installed anchors to meet current code requirements for combined tension and shear given a 16” diameter caisson. Sign base plate anchors will be threaded rods that will be embedded using Hilti’s HY200 adhesive system. I am using Hilti PROFIS to design the anchorage, and increasing the embedment beyond 8" does little to increase tension and shear breakout capacity. Any ideas for an alternative solution? Mechanical anchors (undercut anchors) offer greater capacity but they are not long enough to anchor into the original caisson from the new raised top.
2. The new caisson extension will be reinforced with 6 bars in the perimeter. Do these need to dowel into the original caisson even if the new base plate anchors anchor directly to the existing caisson? If so, would this be a nominal embedment of say 4”?
Yours thoughts on this would be appreciated.






RE: Sign foundation
RE: Sign foundation
Jeff
Pipe Stress Analysis Engineer
www.xceed-eng.com
RE: Sign foundation
Dik
RE: Sign foundation
Don't try to replace that with a 6" embed epoxy anchor
RE: Sign foundation
Is there rebar in the existing 16" dia. caisson? How long is the caisson and what are the sign loads on it? Would it make any sense to break off the top 24 or 36" of the old caisson, to expose the rebar, to be embedded in the new caisson extension with its own additional reinforcing, at about 18" dia? Then, cast a new top extension 24" in dia. This should give you plenty of room for new A.B’s., depth, side clearance, etc. You might even embed the A.B’s. in the top of the old caisson with epoxy, template them at the top and then cast them into the new caisson extension.
RE: Sign foundation
Hookie:
What are your concerns with extending the bored pile?
RE: Sign foundation
A 16" bored pile is not very large, and you don't even know if it is that big. I wouldn't like to be the person who has to drill those holes far enough down to lap with the existing bars. Are the existing anchor bolts corroded? If so, dhengr's solution may be best.
RE: Sign foundation
Thanks for the input. dhengr's approach seems best.
I am also looking at another sign base but this one is a little different, the top of the pile is above grade and the anchors are corroded. Pile diameter is 16". I want to install new anchors to lap with existing embedded rebar and so I am looking at a lap length of 500mm. Anchors would be on a 6x6" template. Can one safely drill 500mm embedment in this scenario? Where can I find guidance on maximum embedment given a certain edge distance?
RE: Sign foundation
RE: Sign foundation
RE: Sign foundation
RE: Sign foundation