What is Rolling Margin?
Rolling margin is the difference between the actual weight of round bars (Reinforcement) Vs. Theoretical weight of round bars. This theoretical weight of round bars pick in IS Codes.
ISÂ Codes 1786: 2008 ( High Strength Deformed Steel Bars and Wires for Concrete Reinforcement, Fourth Revision), this picks in Table-1 Nominal Cross-Section Area and mass, ( Dia Bars: 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 16mm, 20mm, 25mm, 28mm, 32mm, 36mm, 40mm).
This is because of the dia, which is used for casting of rebars. Over a period of time, the shape of dia changes, and as a result, the diameter of the steel bar also changes, which results in a difference in a unit weight of steel.
The size of the die is kept small, and as a result, the rolling margin is negative in the initial stage of production, there after it is more or less close to theoretical weight and then the size of die increases, which results in a rolling margin on the positive side.
As per IS code tolerance for reinforcement as below
As per above tolerance of reinforcement weight
1. Up to and including 10 mins: 4 mm to 10 mm dia of a bar, Individual weight of Up and Down 8%, The Batch weight of Up and Down 7%.
2. Over 10 up to and including 16 mins: 12 mm dia bar to 16 mm dia bar reinforcement, individual weight of Up and Down 6%, The Batch weight of Up and Down 5%.
3. Over 16 mins: 20 mm dia bar to 40mm dia bar reinforcement, individual weight of Up and Down 4%, The Batch weight of Up and Down 3%.
The Procedure of Rolling Margin
Download Format
The above format is used in a rolling margin for reinforcement.
• In this method, one dia of bar minimum three sample requirement, Each sample length minimum 1 m. (1000 mm)
• All the above three sample take the induvial weight, Heter correct length because of cutting of reinforcement not perfect length (Example: 990 mm, 995 mm, 996 mm)
• So Convert in 1000mm length in weight Like 10 mm dia bar 990 length steel weight 0.598 kg, After converting 1000mm length steel weight 0.604 kg, all three weight fill in a block No. 8
• And block No. 9 actual weight of IS 1786, page- 5, table-1 consider
• Block No 10 is a difference between block no. 8 and block no. 9
• Here, Block no 11 is a negative all there sample average difference. Same as block no 12 positive block all three difference.
FAQs
What is rolling margin in the context of steel reinforcement?
Rolling margin refers to the difference between the actual weight of steel reinforcement bars (rebars) and their theoretical weight as specified in standards such as IS Codes (e.g., IS 1786:2008).
Why does rolling margin occur?
Rolling margin occurs due to variations in the diameter of the steel bars during production. Changes in the die size and other factors can lead to slight deviations from the standard theoretical weight.
How is rolling margin calculated?
Rolling margin is typically calculated by comparing the actual weights of randomly sampled steel bars against their theoretical weights specified in relevant standards. The difference between these weights determines the rolling margin.
What are the tolerances for rolling margin as per IS Codes?
According to IS Codes, the allowable tolerances for individual weights vary depending on the diameter of the steel bars. For example, bars up to 10mm in diameter may have a tolerance of up to ±8% individually and ±7% for batch weights.
How does rolling margin affect construction projects?
Rolling margin impacts construction projects by influencing the amount of steel reinforcement required. Deviations from theoretical weight can affect the structural integrity and durability of reinforced concrete structures.
How is rolling margin managed or controlled during manufacturing?
Manufacturers control rolling margin by monitoring production processes closely, adjusting die sizes appropriately, and adhering to quality control measures to minimize deviations from theoretical weights.
What are the implications of negative and positive rolling margin?
Negative rolling margin occurs when steel bars are lighter than their theoretical weights, while positive rolling margin indicates bars that are heavier. Understanding these variations helps in managing material costs and ensuring structural compliance.
How can engineers and contractors account for rolling margin in their projects?
Engineers and contractors account for rolling margin by considering the allowable tolerances in steel reinforcement weights during design and construction phases. This ensures that the specified standards are met for safety and performance.
Are there international standards similar to IS Codes for rolling margin?
Yes, various international standards exist that specify tolerances and requirements for steel reinforcement, similar to IS Codes. These standards provide guidelines for manufacturers, engineers, and contractors worldwide.
What are common methods used to measure rolling margin in practice?
Common methods include random sampling of steel bars, weighing them accurately, and comparing the results against theoretical weights specified in standards. Quality assurance procedures ensure that deviations are within acceptable limits.
