How to calculate cutting length of chair bar

How to calculate cutting length of chair bar,Chair reinforcement cutting length, in this articles we know about how to calculate cutting length of chair reinforcement and what is the main function of chair reinforcement used in slab and footing Foundation.

The reinforcement which are used in chair shaped to support uppercage and lowercage of reinforcement used in footing. And it maintain the constant gap among the upper cage reinforcement and lower cage reinforcement.

There is no any specific IS code and rule is given how to calculate cutting length of chair bar, but in this article we discuss about how to calculate cutting length of chair bar and what is the main function of it and how it is provided in slab and footing.

Why chair bars provided in footing and Slab?

The chair bars provided in footing and slab due to following reason

1) it maintain the constant gap between upper cage reinforcement and lower cage reinforcement in footing

2) it provides vertical support to the upper cage reinforcement and lower cage reinforcement used in footing and slab

3) we know that in tention zone concrete is weak, chair bar strengthen the tension property of concrete.

4) so chair bar improve the the strength of a structure like footing and slab and retain the tension in RCC structure.

5) chair bar provided in footing and slab reduce the chance of collapsing and touching of upper cage reinforcement and lower cage reinforcement to one another and reduce the failure of compression and tension zone in concrete structure.

6) chair bar should be made of scrap Steel it should not be less than 12 mm diameter of Steel bar

◆You Can Follow me on Facebook and Subscribe our Youtube Channel

You should also visits:-

1)what is concrete and its types and properties

2) concrete quantity calculation for staircase and its formula

Structure of chair bar

● chair bar should be made of scrap Steel used in construction site not less than 12 mm diameter of Steel bar it has three component

1) Head of chair bar

2) height of chair bar

3) leg of chair bar

1) Head of chair :– horizontal top part of chair bar which is running cross and below to the upper cage reinforcement to provide support is head of chair ,head is generally provided cover three reinforcement used in uppercage of footing. So head of chair should be sum of two spacing between top main reinforcement addition to 2 lateral sides of 50 mm length of bar.

Length of Head = (2×spacing) +(2×50)

There is two spacing between 3 reinforcement and 50 mm length both side of 1st and 3rd reinforcement used in footing

2) height of chair :- vertical distance of chair bar is known as height of chair, it is main part of calculation to find and how to calculate height of chair bar

Height of chair = depth of footing _ (upper and lower clear cover of concrete + bottom 1bar dia + upper 2 bar dia)

3) leg of chair :- lower part of chair bar is known as leg of chair which is running cross over the the bottom reinforcement used in footing, generally length of leg is provided minimum covering of distance between 3 reinforcement. So length of chair should be sum of two spacing addition to 50 mm length one side extra.

Leg of chair= (2×spacing) +50 mm

How to calculate cutting length of chair bar

1) Head of chair

Length of Head = (2×spacing) +(2×50)

Let spacing= 150 mm between top main two bar and between top 2 distribution bar

Head of chair = (2×150) +(2×50) mm

Head of chair = 400 mm

2) height of chair

Height of chair = depth of footing _ (upper and lower clear cover of concrete + bottom 1bar dia + upper 2 bar dia)

Suppose depth of footing =600 mm

Upper clear cover = 50 mm

Lower clear cover = 50 mm

Bottom bar dia = 16 mm

Top main bar dia = 16 mm

Top cross bar dia = 16 mm

Putting all the value we get

Height of chair = 600_(2×50)_(16)_(16+16) mm

Note :- leg of chair bar is resist over lowermost reinforcement in bottom so diameter of 1 bar should be deducted and head of chair resist below two top reinforcement so diameter of two bar should be deducted.

Height = 600 _148 mm

So height of chair = 452 mm

3) leg of chair

Leg of chair= (2×spacing) +50 mm

Spacing = 150 mm

Leg of chair = (2×150) +50 mm

Leg of chair = 350 mm

4) cutting length of chair reinforcement

Cutting length= (1head + 2 height + 2 leg) _4 bend of 90 degree

Cutting length = [{400 +(2×452) +(2×350)}_(4×2×12)]

Head = 400 mm
Height = 452 mm
Leg = 350 mm
4 bend of 90° = 4× 2d
Dia of chair bar = 12 mm

Cutting lenght = (400+904+700)_96 mm

Cutting length = 2004_96 mm

Cutting lenght of chair bar = 1908 mm