CHAIR BARE IN REINFORCEMENT FUNCTION & HOW TO CALCULATE CUTTING LENGTH.

  What is chair bar ?

            Chair reinforcement or simple chair bars are small structural elements used to properrly place reinforcement  bars in position and maintain tha proper space between tha top and bottom reinforcement.

                 

         Chair bare are mainly used in slab and footing .tha diameter of chair bar should not be less than 12 mm.

                        

Parts of chair bar :

      Head of chair :- tha top horizontal part of chair bar on which tha upper cage reinforcement rests in called head of chair.

      Height of chair :- tha vertical distance of chair bar is called height of chair .

        Leg of chair :- tha bottom vertical part of chair bar is known as leg of chair 

      HOW TO CALCULATE CUTTING LENGTH OF CHAIR BAR : 

          leg of chair bar

 Head of chair :– 

Length of Head = (2×spacing) +(2×50)

height of chair :- 

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

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