Introduction
In the world of construction, even the smallest parts can be super important. One of these parts is called a chair bar. These are small but very necessary pieces that help put the metal bars in the right place when building things with concrete, like buildings and bridges.
What is a Chair Bar?
Chair bars, or chair reinforcements, maintain spacing between reinforcement bars in concrete structures for structural integrity, crucial in slabs and footings, especially raft foundations.
Why Chair Bars Are Used in Reinforcement?
The utilisation of chair bars holds numerous benefits that contribute to the success of a construction project:
1.Precise Reinforcement Placement: Chair bars firmly secure the reinforcement in the desired position, preventing any unwanted shifting during the concrete pouring process.
2.Spacing Maintenance: They play a pivotal role in maintaining the optimal distance between the top and bottom reinforcements, ensuring even distribution of load.
3.Concrete Cover Preservation: Chair bars contribute to preserving the essential concrete cover over both top and bottom bars, shielding them from external elements and potential corrosion.
4.Vertical Support: In footings and slabs, chair bars provide invaluable vertical support to both the upper and lower cage reinforcements, preventing sagging and enhancing structural strength.
5.Robust Support System: By offering robust support to the reinforcement bars, chair bars significantly contribute to the overall stability of the structure.
6.Enhanced Tension Properties: Chair bars aid in boosting the tension-bearing capacity of concrete, ultimately preventing structural failure due to tension zone weakening.
7.Comprehensive Reinforcement Coverage: Properly positioned chair bars ensure that the concrete envelops the reinforcement from all angles, including from the bottom.
8.Tidiness and Precision: Chair bars contribute to the neatness of the construction process, ensuring a well-organised and efficient workflow without compromising on quality.
9.Vibration Stability: These bars prevent the upper cage reinforcement from collapsing during the vibration process, ensuring uniform distribution of concrete.
10.Weight Endurance: Chair bars effectively bear the weight of labourers and fresh concrete, providing additional stability during the construction process.
11.Convenient Longevity: As concrete hardens, chair bars become embedded within the structure, posing no future concerns.
Components of Chair Bars:
Understanding the components of chair bars provides insight into their role and functioning:
1.Head of Chair: This refers to the top horizontal part of the chair bar, upon which the upper cage reinforcement rests.
2.Height of Chair: The vertical distance covered by the chair bar, a critical factor in determining reinforcement placement.
3.Leg of Chair: The bottom vertical section of the chair bar, known as the leg of the chair, offers foundational support for the rebar arrangement.
Calculating Cutting Length of Chair Bar:
Now, let’s dive into a practical example of calculating the cutting length of a chair bar:
Height of footing = 600 mm
Diameter of top and bottom main bars = 20 mm
Diameter of top and bottom distribution bars = 16 mm
Clear cover (top & bottom) = 50 mm
Calculations
Height of chair = 600 – (2 x 50) – 20 – (20 + 16) = 444 mm
Length of Head = (2 x 150) + (2 x 50) = 400 mm
Leg of chair = (2 x 150) + 50 = 350 mm
Cutting length of chair bar = 400 + (2 x 444) + (2 x 350) – 4 x 2 x 20 = 1848 mm = 1.8 m
Conclusion🎯
Chair bars, often overlooked, hold immense significance in maintaining the integrity of reinforcement, optimizing load distribution, and enhancing the overall quality of construction. By understanding their purpose, components, and practical applications, construction professionals can continue to create resilient and long-lasting structures.