Foundation Requirement for 40m High & 2.5m diameter stack

[Eng_Struct]

Hi Group,

I am looking for foundation design guidance for a 40m tall and 2.5m in diameter stack for an industrial building. The native soil is 3m below the finished grade and will mos likely require a deep foundation solution.

What are the design considerations i.e., seismic and wind lateral load, overturning, and sliding? I am thinking a 3.5 (W) x 3.5 (L) x 1.2 (D) concrete pile cap on concrete caissons or H-Piles around the perimeters and in the middle. The push and pull action on the piles will help resist the overturning. I will have to engage geotech to work out the resistance of pile skin friction for uplift/tension. I am thinking I will also require P-Y curves for soil structure interaction for bending moment and shear force values on caissons/H-piles for their design.

1. Any other watch-its or considerations I need to pay attention to?

2. Any design references or guidelines for Canadian industry for the foundation design of stacks will be helpful?

3. My challenge will be designing the pile cap (probably using strut & tie method) to transfer the loads to the caissons/h-piles. Are there any tools out there that can assist with pile-cap design?

Thank you all!

 

[JStephen]

Are you involved in the design of the stack itself? If so, look into vortex-shedding issues that can increase the wind loads or otherwise affect design.
Also watch design temperatures, thermal effects.

 

[Eng_Struct]

Are you involved in the design of the stack itself? If so, look into vortex-shedding issues that can increase the wind loads or otherwise affect design.
Also watch design temperatures, thermal effects.

I am not involved in the design of the stack. Sounds like I will need to request base reactions for the stack from the designer/manufacturer.

How will the temperatures/thermal effect impact the foundation? Are you referring the the base ring of the stack expanding and contracting? If so, I can see that introducing additional axial tension/compression in the concrete pile cap and potentially moment since the load will be applied to the top surface of the concrete.

Am I correct in understanding this?

 

[BridgeSmith]

You'll have a difficult time getting enough uplift resistance from H-piles, or even caissons with the dimensions of the pile cap you've proposed.

If you do drill caissons that close together, you'll have reductions for interaction of the shafts, and you'll almost certainly have to drill and pour them one at a time.

I suspect you're going to need a much larger pile cap, unless you use a single caisson/drilled shaft, which is what I would recommend you consider if the lateral bearing capacity of the soil for the 15-20 feet below frost depth is decent.

 

[Eng_Struct]

You'll have a difficult time getting enough uplift resistance from H-piles, or even caissons with the dimensions of the pile cap you've proposed.

If you do drill caissons that close together, you'll have reductions for interaction of the shafts, and you'll almost certainly have to drill and pour them one at a time.

I suspect you're going to need a much larger pile cap, unless you use a single caisson/drilled shaft, which is what I would recommend you consider if the lateral bearing capacity of the soil for the 15-20 feet below frost depth is decent.

Thanks @BridgeSmith! Good point - I will run numbers to see if I can come up with a practical pile cap size that will result in smaller uplift loading.

For the single caisson suggestion, is a caisson of 2.5m to 3m in diameter even feasible? This will require a steel casing to be driven into the ground first to retain soil, which itself will be custom (welded steel tube). Are there augers in the market with this kind of shaft diameter? I am thinking the steel rebar cage will also be substantial and will require additional considerations to prevent cage from buckling under its own weight.

 

[BridgeSmith]

For the single caisson suggestion, is a caisson of 2.5m to 3m in diameter even feasible?

I assumed a 1.8-2.0m drilled shaft/caisson would be anchored into a larger cap and then the stack anchored to that. Shafts with a diameter of 3m are also feasible, but may not be economical in your area.

 

[canwesteng]

That is pretty hefty for a pile for this application. I'd expect 600-900 diameter, which can be 3D apart, would work well enough. The main thing is to remember the wind acts in any direction, and for a typical pile arrangement wind on a diagonal may well be critical.

 

[HTURKAK]

I am looking for foundation design guidance for a 40m tall and 2.5m in diameter stack for an industrial building.

Is this a flue gas stuck ? What is the material of construction? Steel or concrete?
If there are no constrains for the sizing of the footing , i would prefer hexagonal mat foundation .
If you provide ore info. ( material of stuck , base reactions ..) you may get better responds.

 

[Eng_Struct]

Is this a flue gas stuck ? What is the material of construction? Steel or concrete?
If there are no constrains for the sizing of the footing , i would prefer hexagonal mat foundation .
If you provide ore info. ( material of stuck , base reactions ..) you may get better responds.

The stack is flue gas stack and will be made of steel. The foundation will be concrete.

Thank you for the help!