Drilled Shaft Details

[lutein]

I am seeking help in detailing of drilled shaft foundation system for concrete shear walls. I have some standard details that have been used but want to make sure it's applicable.
Structure is a 14 stories concrete building with stairs and elevators as shear wall cores, i.e. 4 sided box. 36"wide grade beam are spanning between shafts supporting shear walls. Shear walls have tension/compression coupler at each end.

the details I am interested in are:

1. Detail from shaft to grade beam: extend shaft verticals with 90 deg. hook into grade beam. bars will carry shear friction from shear wall in plane shear load.

2. Detail from shaft to shear wall at each end: straight bars from drilled shaft, extended above grade beam and lapped in shear walls. designed for tension coupler at wall ends.

Questions:

1. I wonder if these details are what other engineers have been doing?
2. I wonder if any of you out there are using a big mat or 'cap' over the whole shear core/box footprint? just like what we typically use for auger cast piles.

your help and input will be greatly appreciated. Thank you in advance.

 

[KootK]

Your details seem sound to me Lutein. I usually do use a raft foundation however. My thinking is as follows:

1) I think that the raft may actually be cheaper for stair shafts. The Formwork is easier and the rebar detailing is simpler. At least, that's my opinion.

2) If there's a concrete divider wall, the raft makes for a convenient support for that wall.

3) I usually assume that the wind and seismic shears get transferred to the soil via the piles. With a raft footing, I'm comfortable saying that all of the piles participate I both directions.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hokie66]

I agree with KootK that a pile supported mat makes good sense under a core of a 14 storey building. I can't see what difference the type of piling makes in this decision.

 

[oldrunner]

What does your geotech tell you?

 

[lutein]

Thanks for all the replies.

KootK and hokie66: the shafts are 48" and 60" in diameter. you have a point about formwork and beam reinforcing labor.

oldrunner: the geotech does not touch on grade beam detailing. they have provided us the shaft capacities.