How to Find the Cutting Length of Chair Bar in Footing | Why Chair Bars are Used in Reinforcement

In this Article today we will talk about the Cutting Length of Chair Bar | Why Chair Bars are Used in Reinforcement | Parts of Chair Bar | Chair Bar Segments | How to Calculate Chairs in Slab | Chair Bar Calculation Formula | Chair Bar in Footing | What is Chair Bar

What is Chair Bar:

Chair reinforcement or simply chair bars are small structural elements used to properly place reinforcement bars in position and maintain the proper space between the top and bottom reinforcements. Chair Bar Segments

Chair bars are mainly used in slab and footing. It is one of the most important parts of the raft foundations. The diameter of chair bar should not be less than 12 mm.

Why Chair Bars Are Used In Reinforcement?

The importance of chair bars is considerable. They are used for the following purposes.

1. To hold the reinforcement properly in position.
2. To maintain the distance between top reinforcement and bottom reinforcement.
3. To maintain the cover of top and bottom bar.
4. To provide vertical support to the upper cage reinforcement andllower cage reinforcement in footing and slab.
5. To provide strong supports to the bars.
6. To increase tension property of concrete. Thus it helps to prevent the structure from collapsing due to the fai ure in tension zone.
7. To hold the reinforcement properly so that the concrete may surround the reinforcement from all directions (from the bottom also).
8. To minimize the tidiness of work and to avoid messing up the reinforcement.
9. To hold the upper cage bar from collapsing during vibrating.
10. To withstand labour’s weight and fresh concrete weight.
11. Finally, when concrete hardens, chairs remain trapped in the concrete, making no problem at all for later.

Parts Of Chair Bar:

Head Of Chair: The top horizontal part of chair bar on which the upper cage reinforcement rests is called head of chair.

Height Of Chair: The vertical distance of chair bar is called height of chair.

Leg Of Chair: The bottom vertical part of chair bar is known as leg of chair.

Before Calculating the Cutting Length of Chair Bar you must read this article:

Bar Bending Schedule Basic Formulas | BBS Formula | What is BBS

How To Calculate Cutting Length Of Chair Bar:

The chair bars are placed in the footings to support the top and bottom reinforcement cage as shown below.

You keep it in your mind that, always the top head or supporting part of the chair should be tied to the bottom layer bar ( top distribution bar ) of the upper cage & the bottom leg part of the chair should be anchored to the bottom layer bar (bottom main bar ) of the lower cage.

For your understanding, I have given a drawing of a chair bar showing three parts in it, i.e. head, height & leg.

Chair Bar Calculation Formula:

The cutting length of the chair bar

= [{(2nos.× height ) + (1no. × head ) + ( 2nos. × leg)} – (4nos. × 90° bend )]

Example No.1:

Given Data:

Example No.2: