Tips to find out the cutting length of chair bars

In this civil engineering article, you will learn how to determine the cutting length of chair bar. The purpose of chair bar is to ensure that the reinforced bars can’t be contacted with the framework at the time of loading the fresh concrete.

If it is not provided then the bar is uncovered to the lower surface of slab and thus the corrosion of the bar will occur in due course of time.

So, in order to safeguard the bars, chair should be properly implanted inside concrete mass. The bar chair is utilized to lift them from framework.

Benefits of chair bars :-

It retains the spacing among upper and lower cage.
It helps in safeguarding the bars from collapsing in concrete time.
It provides support to the upper cage.
It raises the strength of the structure & sustain the tension in RCC.

The calculation is based on the following dimension :-

Footing size = 3m x 3m
Height of the footing = 1.2 m
The size of the column = 0.6m x 0.6m
The main bars & distribution bars in footing are provided as 16 mm dia @150 mm c/c

The diameter of vertical bars in footing = 25 mm
The tie bars are provided as 10 mm dia @150 c/c
The cover of footing = 50 mm in all sides
The cover of column = 40 mm

To determine the cutting length of chair bar, initially it is required to find out the height of chair bar :-

The following formula is used for this purpose :-

Also Read: How to work out cutting length of stirrups

Footing Height + [(Upper + Lower Side Cover) + (Upper side main & distribution bar dia + lower side main bar dia)]

After putting the values, we get the following result :-

= 1200 mm – [(50+50) + (16+16+16)] mm = 1052 mm or 1.052 m
The head of chair bar = 50 x d (diameter is provided as 12 mm)
So, 50 x 12 = 600 (the diameter of bar should not be under 12 mm)

Chair bar leg will be calculated as follow :-

Chair bar leg = 2 nos c/c distance + 50 mm (bars which are located at bottom)
= 2 x 150 mm + 50 mm = 350 mm

Now, the cutting length will be calculated as follow :-
[600 + (1052 x 2) + (350 x 2)] – (2 x 4 x 12) mm (as the chair is bent at 4 sides) = 3308 mm or 3.308

Video Source: Under Construction