Old to new foundation 2

[Cyengineer]

Anyone have experience with connecting old foundation to new. This design is what I came up using hilti design software and aci code for rebar development length. Im a bit concerned for future settlement. Do you think using a joint instead may be a better solution?

 

[CovertShear]

You could use mechanical or chemical anchors. HILTI sounds like a good option.

Is it necessary to connect the foundation of the new house wing with the old structure?
Why not construct a dilatation joint? Maybe I am reading the plans wrong.

You should be worried about settlement. Consider evaluating bearing pressure with the added load.

 

[Greenalleycat]

I do a lot of old to new foundation junctions in my work

The answer depends on what your design loads are
If you just want to extend the foundation and transfer nominal compatibility loads then what you have drawn is fine
If you require some sort of anticipated spanning then you will need to increase the embedment of the bars if you want to develop a lap with existing bars - this is relevant here as we have loss of support conditions due to liquefaction in our design guideliens

Consideration of the founding materials is important due to the potential for differing settlement
Presumably the soils under the existing foundation have been consolidated at this point so there isn't much more movement left under static conditions
Your new foundation will be sitting on virgin material and may be prone to some initial static consolidation which could lead to differential issues in the superstructure above
If this is a concern then perhaps specifying some sort of compaction of the excavation base could help mitigate this risk

Also - should you have transverse bars in your new footing?
It seems a bit odd to have hooks landing in effectively an unreinforced lump in the middle then to have two longitudinal bars hanging out by themselves
Perhaps stagger the hooks on your vertical bars alternating facing each way then stick the vertical bars on top of the hooks to give them some support?
And perhaps a longitudinal bar on the inside of the hook?
Up to you though

 

[ldeem]

I don't do a lot of work like this but when I do I try and use smooth bars to connect between foundations. My thinking is I want to prevent differential vertical movement and transfer some out of plane loads. I also want to avoid vertical shrinkage cracks past the dowels. By using smooth dowels any shrinkage can be taken by sliding on the bar instead of developing tensile forces.