welcome back to the channel in todays video we are going to look at How to make a chair bar for over support for steel reinforcements
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.
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.
Rebar-the common term for the metal bar used to reinforce poured concrete-must be embedded to the proper depth (known as cover) in order to provide the proper strength. Rebar chairs, or similar devices, are used to prop up the rebar, separating it from the concrete form or subbase, so that the rebar is embedded in the concrete to the specified cover depth.
There are many types of chairs and other supports available for different applications. Choosing the right support for a particular project depends on several factors, such as the type of surface beneath the concrete, the type of concrete formwork, and the design specifications of the project.
Common support devices include:
Standard rebar chairs
Spacer wheels
Multi-level rebar chairs
Tip (round-cap) spacers
Standard Rebar Chairs
The most common type of chair simply suspends the rebar off the ground so that it becomes fully embedded in the concrete as it is poured. They are often used on foundation footings, concrete slabs, and other flatwork. The chairs may be made of metal or plastic or other non-corrosive material. They provide stability and are lightweight, economical, and easy to install.
Specialty versions of standard chairs include flat-bottom chairs that provide a stable surface and prevent the chair tips from puncturing the vapor barrier under slabs. Standard steel chairs may be fitted with plastic feet to prevent spot corrosion on the concrete surface. There are also stainless steel chairs, which are non-corrosive and are used when plastic is not allowed into the concrete, or when the weight of the rebar is too much for plastic chairs.