How to measure rolling margin of reinforced steel

Rolling margin refers to the ratio of deviation in sectional weight of reinforcement steel permitted according to IS codes. Reinforcement steel is extruded from a mould that is formed with a specific size e.g. 8mm Dia.

When the mould is completely new, the sectional weight of 8mm steel extruded through mould is perfect as per IS standard.

Mould is slightly expanded after specific period of time or after definite quantity of production is acquired from a particular mould. Now equivalent 8mm dia bars extruded from the similar mould will contain more weight per Metre say 0.400Kg per Metre rather than 0.395 as per IS. So, more mass per Metre/Length is necessary for equivalent length.

Given below, the variation in weight as per IS code-1786 for various dia:-

8mm to 10mm +- 7%
12mm to 16mm +- 5%.
20mm and above +- 3%.

Rolling Margin is measured as follow :-

Total Weight of Bars (Dia wise) / Total Running Metre of Bars = Actual Sectional Weight of bars.

Also Read: How to arrange reinforced steel bars in a beam on jobsite

Compare sectional weight with Standard IS Weight.

Weight as per IS Standard = Dia x Dia / 162.

Rolling margin means the differentiation among the theoretical and actual weight of steel. It occurs due to the die that is applied for casting of rebars. Over a period of time, the shape of die alters and consequently the diameter of the steel bar is also modified which leads to create variation in unit weight of steel.

The size of the die is retained small and accordingly rolling margin is negative in the preliminary phase of production, there after it is comparatively close to theoretical weight and then the size of die is raised that leads to rolling margin on positive side.

If the steel is brought from same supplier over a period of time, the rolling margin is rectified and there will be no loss.