How to calculate the length of helical reinforcement bar in the bore pile

Question

How to calculate the length of helical reinforcement bar in the bore pile

Answer 1

 lh = sq.rt.(h^2 + (pi*dh)^2)

basically i know the formula ... but why is (pi*dh) not (dh) only

Answer 2

Try this. Get a rectangular piece of paper, draw a diagonal line connecting 2 of its corners. In landscape view, connect the sides to make it a cylinder. The length of the diagonal line will represent as the length of 1 cycle of the helix.

The length of the diagonal line can be computed using the Pythagorean Theorem; wherein the base is the circumference of the cylinder, the height is the pitch (height of helix), and the diagonal is the length of 1 cycle of the helix.

To apply this in piles, let:
D = pile diameter
d = helix rebar diameter
cc = concrete cover or clear spacing
h = pitch or height
L = pile length
n = no. of helix cycles
lh = length of 1 helix cycle
dh = diameter of the helix cycle

To solve for the no. of helix cycles required,
n = L/h

To solve for the diameter of the helix cycle (diameter of the "cylinder"),
dh = D - 2*cc - 2*(d/2)
dh = D - 2*cc - d

To solve for the length of 1 helix cycle (using Pythagorean Theorem),
lh = sq.rt.(h^2 + (pi*dh)^2)

Lastly, to solve for the total length of helix rebar,
total length = n*lh

Answer 3

L=N*3.18(d+D)+8d
N=Nos of turns
d=Dia of bar.
D=Intrnal dia of cylender