Training 2

FOUNDATION DESIGN


The necessary ultimate capacities of the helical piles are shown in a foundation schedule. These loads are the total live and dead loads determined by typical structural engineering techniques multiplied by the factor of safety for bearing and pullout capacity (usually 2.0 for helical piles).


The installer shall screw the piles until the minimum torque is acquired signifying the necessary
capacity has been reached. The number and size of helical blades necessary to attain the minimum torque depend on the soil stiffness. Characteristically, the installer must depend upon his/her experience with local soil conditions to size the helical blades correctly so that the minimum torque is achieved within a useful depth.

The most reliable method of predicting actual helical pile capacity is the installation torque. Therefore, torque correlations should always be integrated in the design of a helical pile foundation.

It is sensible to advise a minimum length at least equal to 5 helical pile diameters in order for the capacity determination techniques to be valid since they presume a deep failure mode. The engineer may also find it essential to advise minimum helical pile lengths.

 

FORMULAS

Torque is the twisting force that tends to cause rotation. The point where the object rotates is known as the axis of rotation.

T(torque) = F(force) * r(distance from pivot) * sin(theta), where theta is the angle between the force and the position vector. In our case theta = 90. 

Torque -  T = F * r * sin(theta), and it has units of Newton-meters.

T=torque

r=radius

F=force

0=angle between F and the lever arm

L = R x p

L = Length or depth of shaft

R = Revolutions

p = Pitch of the blade

Convert Nm to Ft Lbs - Nm/1.356 = Ft Lbs of Torque

Convert PSI to :Ft Lbs of torque - PSI/12 Inches = Ft Lbs of Torque 

1 kip = 1000 Lbs

A kip is a US customary unit of force. It equals 1000 pounds-force and is used primarily by architects and civil engineers to indicate engineering loads where the pound-force is too small a unit. Although uncommon, it is occasionally also considered a unit of mass, equal to 1000 pounds, i.e., one half of a short ton.

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