HOW TO CALCULATE CUTTING LENGTH FOR SPIRAL STIRRUPS -lceted LCETED INSTITUTE FOR CIVIL ENGINEERS

## Dec 20, 2020

In this article, we will cover how to calculate the cut length of the spiral stirrups in this topic. We know about the helical stirrups used in circular piles and columns. Another term for the stirrups is also called ring or shear reinforcement.

the main reinforcement in RCC structure like column and beam will behold in this closed loop of reinforcements. The spiral helical ring used in the column provides lateral support to the main bar against the buckling, which is applied to the beam and column at right intervals.

Also, they protect the RCC structure from collapsing during a seismic activity like an earthquake. It is used to resist lateral shear stress and diagonal tension stress in RCC structure and provide stability to the reinforcement of Steel bar. let us discuss how to calculate the cutting length of spiral stirrups.

Let's consider as,

GIVEN DATA

The diameter of pile or column = 600mm or 0.6m

Radius of pile or column = 300mm or 0.3m

Spacing or Pitch of spiral bar = 200mm

Length of pile = 10m

Dia of spiral bar = 8mm

Clear cover = 50mm

SOLUTION:

STEP: 1

we find the radius of the spiral and then the length of the spiral ring which completes the one spacing of spiral bar which distance is given in the data,

= Radius of pile (d/2) – clear cover – half of spiral dia bar

= 300 – 50 – 4

= 246 mm

So the length of 1 no of the spiral ring is

= 2Ï€r = 2 x 3.14 x r

= 2 x 3.14 x 246

= 1544.88 mm or 1.5m

STEP: 2

Find the number of spirals, then find out how many laps are needed in the total length of the spirals

NUMBER OF SPIRAL

Number of spirals = length / spacing of spiral+ 1

= 10000 / 200 + 1

= 50 + 1

= 51 nos

51 nos of the spiral are completed for spiral bar in this length of given column or pile.

So, Total Length of the spiral bar is

Total Length = No Of Spiral x Radius Of The Pile

= 51 x 1.5m

= 76.5 meters

We know that the length of a whole bar is 12m, so lapping is necessary in this case.

No of laps = total length of spirals/length of one bar

= 76.5 / 12

= 6.29 say 7 nos

7 nos of laps are required

In general, lap length is 50d which means 50 times the bar diameter

where d is dia of bar

= 50 x 8 = 400mm or 0.4m

Total length of spiral bar

Total length of laps = 7 x 0.4 = 2.8m

Total length of spiral rings = 76.5 + 2.8 = 79.3m

Total weight of spiral rings

= d2/162 x length

= 82 / 162 x 79.3m = 31.32 kg

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