Sign foundation 1

[GalileoG]

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.

 

[hokie66]

My thought is to support the new sign post at the same level as the old one, and protect the base. Extending the bored pile does not pass my smell taste.

 

[JGard1985]

Look at Drill-co maxibolt undrcut anchors, you can get them extra long if you need to

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[dik]

Can you use higher strength stainless steel threaded rod, with an extended base? The Hilti adhesive anchorage is good and you may want to check with Hilti to see what threaded rod they could recommend.

Dik

 

[hawkaz]

Don't be afraid to go deep with epoxy. Quite often- the bolts that show up with signs and light poles are very long (I have seen 42" in some cases)
Don't try to replace that with a 6" embed epoxy anchor

 

[dhengr]

GalileoG:
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.

 

[GalileoG]

Thanks all for the input.

Hookie:
What are your concerns with extending the bored pile?

 

[hokie66]

I am not a Hookie, but rather a Hokie.

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.

 

[GalileoG]

Sincerest apologies Hokie, you are a familiar name but I've always read your name in my head as "Hookie"

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?

 

[hokie66]

With only a 6" x 6" group, it must not be a large sign. So yes, you can drill 500 deep. Will just need some long bits and a good drill.

 

[Leftwow]

We encounter this a lot with long pedestals. This is where edge distance takes into effect. Your anchor bolt design depth depends on breakout area, so if the breakout area stays the same you can count on your design strength for breakout in appendix D to actually reduce. I think one person mentioned before that if concrete reinforcement is an x distance away from your anchor bolt you can count that as reinforcement for the anchor bolt, significantly increasing the strength which is Hilti Profis most likely doesn't take into account. Appendix D doesn't guide you through this but Canada has a code that allows you to figure out how much strength you are actually getting from it.

 

[GalileoG]

If I am drilling deep, there is a risk that the drill bit might go through the conduit that illuminates the sign) at the centre of the pile where it bends into the soil. The bend is usually 2’ below grade but I imagine its depth can vary significantly. Is there any way, other than not drilling at all, to mitigate risk of drilling through the conduit and in particular the bend in the conduit which is deep in concrete?

 

[jayrod12]

dig around the pile to determine where the conduit exits the pile. This should allow you to locate the approximate location of the conduit.