Holdown anchor through existing footing

[AaronMcD]

Wonder how you all detail a holdown anchor through an existing footing.

Do you bolt it directly to the bottom of the concrete and allow deformation or crushing at the rough surface? Do you extend a distance below the footing and cast it in? Is there a need to use rebar or does a block of plain concrete work? Does water intrusion corrode the anchor? What else am I missing?

Thanks.

 

[structSU10]

What exactly are you trying to accomplish? If you don't have sufficient concrete thickness to accommodate an epoxy dowel or similar you may be better off demolishing and rebuilding to suit the new construction.

 

[AaronMcD]

There is enough thickness, it is a 16" wide by 20" thick footing.

10" is the maximum epoxy embedment and that is not strong enough for overstrength or ductility.

Originally we assumed a 12" thick footing, and specified a new 16"x16" footing below with t&b rebar. Now that we know the existing footing is so thick we have enough existing ballast and just need to go through the existing footing.

 

[Heaviside1925]

10" is the maximum epoxy embedment

Is this limited by rod diameter? Can you use a larger diameter rod and couple/reduce it to the required anchor size?

 

[AaronMcD]

Is this limited by rod diameter? Can you use a larger diameter rod and couple/reduce it to the required anchor size?

That's an idea. There is a stem wall they would have to remove and replace. There is no push back to going underneath.

 

[Heaviside1925]

allow deformation or crushing at the rough surface

This doesn't feel right, not saying it would be ok. If going this route, I'd be inclined to use a steel plate on the bottom, grout between plate and bottom of the footing, with the rod extending through.

 

[bones206]

Sounds like an undercut anchor might be a good solution here.

 

[AaronMcD]

Sounds like an undercut anchor might be a good solution here.

I glanced at a few but none long enough.

 

[Aesur]

I second the steel plate on the bottom and grouting around for proper concrete cover over the steel.

 

[BridgeSmith]

Sounds like an undercut anchor might be a good solution here.

I glanced at a few but none long enough.

Can you extend them with a coupler nut and all-thread?

I would caution that using epoxy anchors for tension applications requires very strict QC/QA, particularly in the thorough cleaning of the holes and the thorough mixing of the epoxy components.