The quantity of Steel is usually derived from the drawings using Bar Bending Schedule. The quantity of Steel arrived used bar bending schedule is usually in length of each diameter of bar required.
How To Derive The Formula For Weight Of Steel Bar?Here I am willing to explain how it has been arrived D2/162 (Note: D unit is in MM)Density of Steel (in Kgs/Cu.m) = Weight of Steel (in Kgs)/Volume of Steel (in Cu.m) So
Weight of Bar (in Kgs) = Volume of Steel Bar (in Cu.m) X Density of Steel Bar (in Kgs/Cu.m)Data:
Volume of Steel Bar (Cu.m) = Area of Steel Bar (sq.mtr) X Length of Steel Bar (m) Since We are trying to calculate the unit weight of Steel Bar, the length of Steel Bar in the calculation would be 1 m or 1000 mm.
Area of Steel Bar = (3.14 X D^2)/4Density of Steel Bar = 7850 Kgs/Cu.m = 7850/(1000X1000X1000) Cubic mmSo considering these data in the Weight formula we getUnit Weight of Steel Bar (in Kgs) = (3.14 X D^2)/4 X 1000 X 7850 / (1000 X 1000 X 1000)
= D^2 X (0.006162)
To simplify, we can reciprocate the decimal figure here i.e., (1/0.006162) and get a figure of 162.28Unit weight of Steel Bar (in Kgs) = (D^2)/162.28 ~ (D^2)/162Where D is the Diameter of the Steel Bar in mm.
How To Measure The Weight Of Steel Received At Site?Since it is hard to weight the bars at site, Trucks carrying steel (Gross weight) and empty truck (Tare weight). Steel Weight can be calculated by the following formula
Reinforcement Steel received at Site (in Kgs) = Gross Weight – Tare WeightDiesel allowance (30-40 Kgs) is diesel consumed between obtaining the two weights This Diesel allowance needs to be deducted incase the weigh bridge is far away from the Site.
Lap length is one of the important terms in the reinforcement. This is usually confused with another important term called development length and anchorage length.
During the placement of steel in a Reinforced concrete structure, if the required length of the single bar might fall short. To get the desired design length, the lapping of two bars side by side is done. An alternative to this is to provide mechanical couplers.
The overlapping of the steel is very important in R.C.C works because splicing of steel is used to transfer all the stresses from one bar to another bar. The length of the lapping is different in different concrete mixes because different concrete having a different crushing strength.
1- The lapping is not provided above 36 mm diameter bars because those diameter bars doesn’t transfer the stresses from one bar to another bar and also the alignment of the column bar is also affected by providing the lap on these bars.
2- The lapping of the steel bars also not provided in high shear force zones and it should be provided at that zone where the shear force will be minimum.
In M 15 Concrete Mix: In M 15 we use the concrete mix 1 : 2: 4 means 1 part of cement, 2 part of sand and 4 part of aggregates.
Tension zone Compression Zone
Fe 250 – 55 ∅ Fe 250 – 45 ∅
Fe 415 – 57 ∅ Fe 415 – 47 ∅
Fe 500 – 68 ∅ Fe 500 – 57 ∅
In M 20 Concrete Mix: In M 20 we use the concrete mix 1: 1.5 : 3 means 1 part of cement, 1.5 part of sand and 3 part of aggregates.
Tension zone Compression Zone
Fe 250 – 46 ∅ Fe 250 – 37 ∅
Fe 415 – 47 ∅ Fe 415 – 38 ∅
Fe 500 – 57 ∅ Fe 500 – 46 ∅
In M 25 Concrete Mix: In M 25 we use the concrete mix 1 : 1: 2 means 1 part of cement, 1 part of sand and 2 part of aggregates.
Tension zone Compression Zone
Fe 250 – 39 ∅ Fe 250 – 32 ∅
Fe 415 – 41 ∅ Fe 415 – 33 ∅
Fe 500 – 49 ∅ Fe 500 – 39 ∅
Where ∅ is the diameter of the bar? Suppose we are using a steel bar Fe 500 and concert mix M25. The diameter of the bar will be 10 mm. By using the formula, the splice length of the steel bar will be 49 x 10 = 490 mm and if the bar is in tension zone and 39 x 10 = 390 mm if the bar is in the compression zone.
