Pile Foundation Design

[CBSE]

I'm working on my first Pile Foundation supporting building in about 8 years...which was done at a company I no longer work for. It's a really simple building, one story, rectangular 90x60, and an Essential Facility.

Questions I have:
1) I received the soils report from the Geotech and I have vertical load capacities for 10" & 12" diameter piles hollow steel piles. Is it my responsibility to determine the steel wall thickness of the piles? I can't find it anywhere in the Geotech Report.
2) Is it more preferable to fill these with Concrete or weld a 1" thick by 14" square steel cap on them with headed nelson studs? I have my detail created for filling the pile with concrete, but was asked to show one with a steel cap as well.
3) For my lateral loads on the building, I'm assuming the Geotech will need this info to determine whether or not the Pile Spacing I have determined as adequate will work?
4) Do I need to check the steel piles for bending adequacy from my lateral load calcs?
5) Does anyone have any good references for structural notes for piles that I could look at?

Thank you!

 

[jayrod12]

1) Yes, however the piling contractors in your area should have standard sizes that they generally use.

2) Filling with concrete is generally a waste of concrete. We've done the plate with nelson studs, or plate with weldable rebar.

3) Is the geotech going to check the piles for lateral (unlikely) or just provide you with soil properties that will allow you to check lateral resistances for your piles(more likely)?

4) Yes, the key here is knowing how far down into the soil you need to consider your pile is subject to bending.

5) Unfortunately I do not but someone else here might.

 

[CBSE]

Thanks for the info.

 

[BigH]

I would suggest that you might wish to consult M.J. Tomlinson's book Pile Design & Construction Practice - 5th Edition. Has a whole chapter on Structural design aspects - as well it is a dang fine book to have for pile design and construction. (note - any of the editions are good . . .)

 

[CBSE]

Attached is my pile cap detail. Does this look reasonable? My grade beams are 14" and 12". I used a 20" square cap for all conditions which gives me 3" of tolerance if the pile is misplaced.

 

[jayrod12]

If it were me, I would likely provide the pile cap with it's own vertical reinforcing located as close to the outside face as allowed and then provide the ties around that rather than just providing the ties around your pile reinforcing.

But that's just my thought, I doubt it would be a requirement.

 

[CBSE]

Good catch. Thanks!

 

[cetiger]

I agree with Jayrod12 regarding his recommendation for relocating the vertical reinforcement. If I could offer another suggestion...I would avoid welding the #6 verts to the steel cap plate. I see you have the correct grade, etc. called out, but if you do some research on weldability of rebar and the process to do so, it is very difficult to achieve in the field. The process works great in a lab under controlled conditions, but outside in the open environment, this can be tricky to accomplish. If not done incorrectly, welding on rebar can actually make it brittle due to the amount of heat induced in the bar during the welding process. Again this has to be done by a certified welder who has experience doing this, which in my experience can be hard to find. In lieu of welding the #6 verts to the steel cap plate of the pile, I might suggest extending the steel pile and cap plate up into the grade beam or making the grade beam deeper (locally) around the steel pile and encompassing the cap plate. I would then provide a reinforced cage around the pile cap within the grade beam that the #6 verts could then be embedded into to achieve the connection to the slab on grade above. Doing it this way would most likely be cheaper, faster to construct, and again avoid the risk of not performing the welding correctly. You may add a little more concrete and reinforcement, but I think that would be a minimal cost compared to paying a welder's labor.

 

[CBSE]

cetiger:

I'm not sure I entirely follow. How would I run my bottom bars in the grade beam past the steel pile? I suppose I could specify bar bends to occur so that the bars can transfer around? Do you have a sketch of one you have done like this?

For welding of the rebar, I was contemplating specifying that the bars be welded in a controlled environment to remove the field weld issues.

The other alternative was to use Nelson Headed studs instead of the rebar, but I like the rebar better.

 

[KootK]

Assuming that you're not attempting to take slab moments into the pile, I would absolutely use Nelson studs. I'd also make the "cap" just a concrete thickening that extends maybe 6" below the floor slab. Lastly, I'd make that thickening at least 6" wider than the pile cap plate on all sides to account for tolerances. Unless I'm missing something regarding the function of the joint, what you've shown strikes me as considerable overkill.

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

 

[CBSE]

The only load I'm intending on transferring into the pile is vertical and horizontal (wind/seismic).

 

[KootK]

Then this may be an attractive alternative for you. It's probably better load transfer for wind and seismic. I should have drawn the cap plate embedded.

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