Torsion transfer to pile

[allimuthug]

I have a pile cap with two piles.The Fz in the pedestal causes torsion in the pile cap. If the concrete in pile cap has enough capacity to take torsion, torsion reinforcement is not required. But the torsion in the pile cap should be transferred to the pile.
Can anybody explain me weather i am right or wrong. Kindly explain me in detail the force transfer from pile cap to pile for force Fz.
Link

 

[Retrograde]

The force Fz will cause bending Mx in the piles that needs to be designed for. Any torsion My in the piles would be only a "compatibility" torsion and can therefore be ignored (provided you are not relying on it to reduce the bending moment My in the pile cap).

 

[allimuthug]

Hope you didn't understand my question can you explain me force tranfer

 

[zakmuh]

Hi,

Convert the torsion (Mtorque) into horizontal force, then apply to the pile. If you already have a Hforce acting on the pile, add this up to that.

Cheers

 

[hokie66]

Retrograde's answer is correct. The torsion in the pile cap becomes a bending moment to be resisted by the two piles. Or you can just take Fz/2 to each pile, which gives you a shear and a bending moment.

 

[allimuthug]

So the torsion is transfered as moment to pile, it means the tension from distribution bar has to be transfered to the pile rebar. Please confi this

 

[KootK]

Assume "y" to be the vertical distance from the top of pile to force Fz. Each pile will experience the following due to Fz alone:

1) V = Fz / 2
2) M = Fz x y / 2

From there, each pile will need to transfer force in a manner very similar to what we've discussed in past threads where we were talking about single pile systems.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

A sketch of the the load path is shown below. I asked a related question recently regarding the detailing at the cap/pile connection: Link. You may find that relevant to your problem.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[allimuthug]

If the concrete has the capacity to take torsion.then the compression and tension force from concrete is transfered to the pile rebar.
If the torsion in thel pile exceeds the concrete torsion capacity, then reabrs are provided to carry torsion.hence the torsion from steel has to be transfered to the pile rebar.for this The width of the pile cap has to be reduced.kindly clarify me weather my statementl is right.

 

[KootK]

If the concrete has the capacity to take torsion.

This is the part that requires care. At the proportions you've drawn your system, sectional method torsion checks, as you might use for a regular beam, don't really apply. Strut and tie is more suitable.

Regardless of how you choose to check cap torsion, you're going to have three column/beam style connections in close proximity to one another. Expect plenty of rebar.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[allimuthug]

Could you please send me an example problem for the above.I don't know how to calculate the rebar detail. I was thinking that I should check for beam torsion only.

 

[KootK]

Link

I'm afraid that I'm not aware of any worked examples although I'm sure there are some out there. Maybe try TXDOT research reports on STM methods.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[allimuthug]

If my torsion is very less, and concrete could take torsion. No need of rebar for torsion.