Torsional capacity in drilled piers
Torsional capacity in drilled piers
(OP)
I am working on a drilled pier design software. I would like to add torsional resistance and am very interested in the different equations and approcahes used worldwide. The program already has axial downward, uplift, lateral and moment loads. In addition it will have reinforcement design per ACI 318-11. Adding torsional capacity is the missing link. Thanks.






RE: Torsional capacity in drilled piers
RE: Torsional capacity in drilled piers
RE: Torsional capacity in drilled piers
You should be checking the frictional resistance between the concrete and soil against rotation of the entire pier.
RE: Torsional capacity in drilled piers
ACI 318 has provisions for torsion design in Chapter 11.
RE: Torsional capacity in drilled piers
RE: Torsional capacity in drilled piers
The skin friction value is normally in the soil report. I agree it's not a lot that's why the rotation of the entire pier would typically govern vs. the development of torsion in the pier itself.
RE: Torsional capacity in drilled piers
If you assume the fixity point is too high up the pier (too shallow a depth) then you run the risk of underestimating pier rotation.
If you assume it too low, then you would overestimate the pier rotation.
But assuming a single point of fixity may not be entirely accurate either as the soil will deform to some extent along with the pier and nailing down the actual shearing stresses in the soil would be difficult.
The pier torsional design seems to be straightforward - there is an applied torque at the top of the pier and you would need to determine adequate torsional ties as well as longitudinal reinforcement for that.
RE: Torsional capacity in drilled piers
It has been a long time since I have used it, but FDOT had several Mathcad templates for auger cast piles. I believe they were available to the public on their website, you can probably do some online research and find them.
RE: Torsional capacity in drilled piers
RE: Torsional capacity in drilled piers
JAE, you explain the plan torsion but how about the eccentric shear load torsion - see attached diagram?
RE: Torsional capacity in drilled piers
If you assume an X, Y, Z axis on top of the pier with Y vertical and X and Z horizontal directions, then I'm talking about My (moment about the y axis) which is pure torsion in the shaft of the pier.
If there are shear forces laterally (Fx or Fz) then they would simply apply direct shear to the shaft, not torsion. If Fx and Fz are eccentric to the center of the shaft, then they would each have My components to the shaft which would just be added to any other applied My value.
RE: Torsional capacity in drilled piers
RE: Torsional capacity in drilled piers
The current research is a pile system that is water jetted into the ground and then pressured out into the soil mass, instead of relying on skin friction of an auger cast concrete pile. The values in torsion and bearing are impressive.
RE: Torsional capacity in drilled piers
http://www.soilstructure.com/