All about civil construction knowledge- PARAM VISIONS

What is chair bar in construction work?/ Spacing & purpose of providing chair bars in construction.

 Now, let us go through some of the FAQs related to the chair bar used in the construction work.


1.  What is a chair bar in construction?



A chair bar is a support bar placed and tied in between the upper & lower reinforcement cage to maintain the gap and stability of reinforcement. As they are somewhat bent up like a chair, and provides a sitting arrangement for the upper cage, we call it, a chair bar in civil engineering.


2.  What is the purpose of providing a chair bar in construction reinforcement?



1. To maintain the required gap between the upper & lower reinforcement cage in footings, slabs, raft foundations, etc.

2. To maintain the clear cover for the reinforcement at the time of concrete vibration.

3. Protecting the top & bottom cage from displacement and sagging at the time of concreting work, due to the movement of trolleys, walking of the workers, dead load of the fresh concrete, etc.

4. Providing extra support for the reinforcement bars.


3. What should be the diameter of chair bars used in construction?

Generally, the chair bars are made of rebars of diameter 12mm and above. The most common dia. bars are 12mm, 16mm, and in some cases 20mm. 

In rare cases, it is OK to use 10mm bars in slabs, when there is no extra external load other than reinforcement cage load. 

The reason for not using the smaller dia. bars ( < 12mm ) is, they tend to bend or buckle for the overladen loads due to which, the main purpose of providing the chair bar becomes useless.


4. What should be the spacing of chair bars in construction?

The spacing of the chair bars depends on several factors like,

1. Diameter of the bar used in making a chair. 👉 The larger the diameter of the bar, the more the spacing is, and vice versa.

2. Type of the structural member.

3. Diameter of the reinforcement bar of the RCC structure.

4. External loads that act over the chair bar other than rebar cage.


As such, there no specification for the spacing of chair bars in the construction.

In general, 1no. of chair bar is provided for the reinforcement cage area of 0.8sqm - 2sqm., depending upon the above factors.


5. What is the number of chair bars required in 10sqm. of structural reinforcement area?

Let us consider providing 1no. of chair bar per sqm. area of RCC structure.

The no. of chair bars 

  = Area of structural reinforcement in sqm ÷ chair bar per sqm.

  = 10sqm ÷ 1sqm.

  = 10nos.

 





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