Rebaring technique in reinforced concrete construction is a method for proper fabrication and placement of reinforcement bars as per the design and drawings for RCC works.
We know that, concrete is very strong in compression and weak in tension. The reinforcement bars or rebars are good in tension, that are incorporated with concrete to make use of its tension property.
Estimation of reinforcement bars for a reinforced concrete work is done by the engineer in charge. The engineer provides us with the specific details of the number of reinforcement bars, the shape and size of each bars for each work.
There are different types of loads that including tension, compression, lateral, horizontal and torsion that are forms of pressure, against which the concrete has to show its strength.
The strength gained by the R.C.C structure is dependent on the method, as well as the techniques that are employed to install the reinforcement bar. The reinforcement bars are mainly patterned over its surface to facilitate proper bonding with the concrete.
Necessity of Rebaring Technique in Reinforced Concrete Construction
The steel reinforcement mostly is divided into two categories i.e.
- Primary Reinforcement or Main Steel reinforcement
- Secondary reinforcement or distribution reinforcement
Main steel reinforcement bars are employed in R.C.C structures to ensure resistance against the whole design loads coming over it. The secondary reinforcement bars are mainly employed due to durability as well as for aesthetic reasons.
This reinforcement guarantee resistance for localized areas, like limited cracking. These also offer resistance against the stresses that are created due to temperature variations.
The main bars employed of specified diameter are bent at the ends. The stirrups are reinforcements that are provided laterally, to keep the main bars of the structural elements like beams and columns, in position.
The stirrups may be circular, square, rectangular, helical or diamond shape based on the cross-section of the structural element. The reinforcement bars in the corners may be L – shaped.
The caging for the structural element under consideration must be properly tied, so that during concreting no bar is disturbed from its position. This is a check to be always kept in mind during concreting, else it is a threat to the durability of the structural member.
The rebars are mainly provided at the junctions where the formwork of the structural element is closed as well as at the point where a new structural element needs to be bond with the former one.
Operations in Rebaring for Reinforced Concrete Works
The three main operations carried out in rebaring for reinforced concrete construction bars are cutting, bending and tying. The diameter of reinforcement bars used reinforced concrete work mainly ranges from 6 to 42mm. These reinforcement bars come from the steel mill in specified lengths.
So, during installation, the reinforcement bars must be cut into required size. The design engineer shows the details about the bars bending and related works, based on which the workers proceed the work. The rigid connection is made between all the members of the rebars with the help of steel wires.
Equipments used for Rebaring Techniques
The equipment that is used for rebaring operations is developed with time, as the size of bars is increasing. Larger size bars are difficult to be handled by hand operation.
The usage of chisel and hammer was an earlier practice used for bar bending. The bar is held fixed with the help of three thick bars over a bar bender bench. Then the bending is done by means of manual force, operated with the help of levers. To tie the rods, cutting pliers were used, and tied by steel wires.
The enormous demand for work and bars with large diameters have made to depend on machines for bar bending. This improved method helps in reduction of time consumed by an ordinary method.
Different Types of Rebaring Equipments are:
The different equipment that is used for rebaring based on cutting, bending and tying operation are explained below.
Equipment used for Cutting of Reinforcement Bars
1. Electric Rebar Cutters
Electrical cutters that can cut diameters up to 16mm are employed. These consume power to cut the bars. Higher varieties are available in the market.
2. Heavy Duty Rebar Cutter
These are a higher version of the same, the heavy-duty cutters, that have the capability to cut the bars up to 42mm. At a time, these cutters can cut three to six bars at a time. These cutters make use of oil bath lubrication, that makes the operation noiseless. The system is simple and hence easy to use.
3. Wire Rope Cutter
The cutting blade of wire rope cutters is made of steel with a titanium coating. They have a high-speed cutting. These cutters are employed to cut the bars up to a diameter of 20mm. They cut a single bar within 8 seconds, so fast and so clean cut.
4. Rebar Cutting Shear
Rebar cutting shear is a cutter used to cut the stirrups at the equal size in a huge amount. These can also be used for cutting the pipe section, angle or channel sections.
Equipment Used for Bending of Reinforcement Bars
1. Electric Automatic Rebar Benders
This machine helps to bend the bars either on site or at the workshops, based on the convenience. The machine is noiseless. It operates only during the bending procedure.
2. Spiral Hoop Radial Benders
This machine is used to get radius in the bars that are of higher diameter. It has rotating rollers, of which one is adjustable to hold the bars.
Equipment used for Tying of Rebars
As in rebar cutting machines, the rebar tying machines too are available, both manmade and automatic.
1. Manual Rebar Tying Machine
Manual rebars have a net weight of 680 to 700 grams, which can be used to tie a combination of bar size. Their size is mostly in the range of 300mm x 25mm. These are cheap and can be used for any working or weather conditions.
2. Automatic Rebar Tying Machine
There are automatic rebar tying machines that can help tying bars up to a range of 32mm. It requires 16 seconds for each tie. These rebaring machines can facilitate completion of a large volume of work within limited time. This method does not compromise on the quality as well as efficiency.
There are many agencies, that supply the bar bending, cutting and tying operation, based on the set of specifications provided to them. These suppliers also advise whether the concrete formwork must fully or completely erected before they are ready to supply the tied-up bars as per specification.
Safety During Rebaring
To prevent injury, the bars that are extended intentionally for later work must be covered with any plastic caps or “plate caps”. There are certain caps called mushroom caps, that too can be provided so that scratches or injuries can be avoided.