Cutting length calculation of spiral or helix reinforcement cage for piles

In this civil engineering article, you will learn a simple process to determine the cutting length of spiral or helix for pile reinforcement cage design as well as quantity of steel.

The purpose of the pile cages to increase the strength of vertical concrete columns normally when the soil is weak or deep foundation should be provided.

Column sizes and designs fluctuate with application, and several different assembly methods are required to make sure that the concrete reinforced columns are manufactured based on the utmost effective standard.

Pre-fabricaged pile cages are provided to site completely assembled; welded or tied, or delivered in their component parts to be assembled on site.

The calculation is done based on the following data :-

Diameter of pile is given as 1.5 meter.
Depth of pile is given as 20 meter
Pitch of spirals or spacing of spirals is taken as 100 mm or 0.1 meter
Diameter of spiral bar is taken as 12 mm.

The concrete cover is taken as 50 mm or 0.05 meter.

Initially, it is required to work out the net dia of spiral in caging as follow :-

Total diameter - (2 x cover both sides)

= 1.5 - (2 x 0.05) = 1.4 meter

So, net diameter of caging = 1.4 meter

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After that, it is required to calculate the circumference of one spiral as follow :-

πd = 3.1416 x 1.4 (as value of pie = 3.1416) = 4.4 meter

Now it is necessary to determine the numbers of spirals as follow :-

Depth of pile /Pitch + 1 = 20/0.1 + 1 = 201 numbers.

Now, determine the total cutting length as follow :-

Circumference of one spiral x Numbers of spirals = 4.4 x 201 = 884.4 meter

So, for 20 meters pile, 884.4 meter long spiral should be cut.

The quantity of steel will be calculated as follow :-

We know, for 1 running meter, the weight of bar with 12 mm diameter is 0.888 kg. It is the unit of bar. It is derived by the following formula :-

d2 / 162 = 12 x 2 / 162 = 0.888 kg.

To determine the quantity, the following formula is used :-

Quantity of 12 mm dia bar = Total cutting length x unit weight = 884.4 x 0.888 = 785.35 kg.