Minimum Shear reinforcement for Short Piles 1

[engr.levy]

I had a discussion with my supervisor regarding the minimum shear reinforcement for piles.

This case our pile was a short pile with bid diameter and the lateral loads governing.

I am just confused on the shear reinforcement as I am designing the reinforcement for the actual Vs requirement, while my supervisor insists on using the minimum shear formula for beams.

The code does not clearly states what to do as on the pile code it says you can design as column, and on column section it points you to beam sections. Which the minimum shear formula comes from.

The minimum Vs formula produces big value and I found it unreasonable for a pile that is supported on its length and I assume as short pile the soil will fail first before reaching any failure on the strength of the pile.

Could you help me guys what's the proper logic to this or if this is stated in any code section?

Thanks.

 

[centondollar]

A short pile is in practice not supported along its length; it will rotate as a rigid body in failure, and the large localized soil pressure will cause a significant shear force. Long piles are supported along their length, mobilizing the soil (often portrayed with winkler springs) and spreading out the effects (deflection and associated shear and bending) along the pile length.

The code will not tell you how to perform detailed structural analysis. I suggest that you find examples of short pile design formulas and derive approximate pile internal shear forces using those. The method by Broms (developed during the 1960s) is one of many options for approximating short-pile behavior against lateral loading.

 

[RPMG]

The minimum tie requirements are not applicable when:
1. It is designed as a plain concrete pedestal.
2. Or half the concrete strength is sufficient to resist shear.

It's my preference to design simple block sections as plain concrete, and then reinforce them anyway for ductility.

 

[engr.levy]

The minimum tie requirements are not applicable when:
1. It is designed as a plain concrete pedestal.
2. Or half the concrete strength is sufficient to resist shear.

It's my preference to design simple block sections as plain concrete, and then reinforce them anyway for ductility.

How about Vu>Vc but the Vs shear requirement is less than the minimum shear formula? The Vs only requires 12-200mm ties but the minimum shear formula requires 16-200 (due to large diameter of pile)

I am just not sure if we are required to satisfy the minimum formula for columns or piles.

 

[RPMG]

Use the minimum. The Phi-factor assumes a ductile failure. It was calibrated with a minimum area of steel in mind. If the minimum is not met, the formula for calculating Vs is not applicable.