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Calculations for Steel Rebars Weights

 

How to Calculate Weights of Steel Bar Reinforcement in Reinforced Concrete Works

Reinforcement for Concrete Works may consist of Round Bars, Deformed bars, and Welded Mesh fabric and are used in concrete slabs, walls, beams, columns. For estimation of quantities of rebars for the purpose of costing is based on total weights in Kg or Tons.

For Normal Reinforcements 

 Rebars Picture The following Table 1 below gives Bar Reinforcement weights, irrespective of whether the bar is round, deformed, mild steel or high yield, unit weight is the same:
 Table 1 

Bar Diameter

Unit Weight

Sectional Area

(mm)

(kg/m)

(mm2)

6

0.222

28.3

8

0.395

50.3

10

0.617

78.5

12

0.888

113.1

16

1.578

201.1

20

2.466

314.2

25

3.853

490.9

32

6.313

804.2

40

9.864

1256.6

To obtain weights simply select the Bar Diameter and the corresponding weights in kg/m and calculate as follows :

Bar Dia (mm)

Unit Wt, (kg.m)

Length of Bar (m)

Total Weight (kg)

 12

0.888

5

4.44

It would be easier if you use a simple spreadsheet to prepare the table, or simply download a copy here

For Mesh Reinforcement Fabric

 Mesh Rebar Fabric Picture Pre Welded Mesh rebars are commonly used for slabs and walls, especially those with large and uniform areas as these can be purchased quickly, and placed easily without the need to check quality or spacings.

Unit weight for Mesh Rebars can be obtained from the manufacturer or based on the British Standards typical fabric types given in the Table 2 below. Note that there are several Fabric Types depending on the standard used, so a check with the manufacturer is necessary.

 Table 2 

Ref

No

Unit Weight

Fabric Type

 

 

(kg/m2)

 

A

393

6.17

 Square 200x200

A

252

3.95

 Square 200x200

B

785

8.14

 Structural 100x200

B

503

5.93

 Structural 100x200

C

785

6.72

 Long Mesh 100x400

C

503

4.34

 Long Mesh 100x400

D

49

0.766

 Wrapping 100x100

D

31

0.493

 Wrapping 100x100

To Obtain Total Weights, simply multiply the Unit Weight by the Surface Area Covered.

Using a Spreadsheet in a table form and a proper take-off sheet would make quantities take-off easier, more organised and accurate. You can download a copy here

click to enlarge

For Slabs & Walls Reinforcements

Slabs and walls normally have rebars in two direction in a mesh form as in Fabric layout, however the spacings of rebars are not standard, eg: T16mm dia, 125mm x 200mm. In this case you would need to develop a similar Unit Weights in kg/m2 so that quantities can be taken off based on metre square rather than counting individual bars. You can obtain a sample copy here

Wastage in Rebars

For quantities estimation of rebars, due allowance should be made for wastage and if you like can include a factor for site, locality & local practices. Quantities should be taken to the nearest tons. For small projects, you may want to purchase in Individual Bars and in this case you need to convert the total weights in kg to the nearest standard delivery length, usually 12m.

Generally for wastage allow about 2.5% for standard cut and bent bars, 5% for standard precut lengths, and 10% for random lengths. Again discretion is advised as if site logistics is far and difficult then allow 20% or more, while for easier logistics, purchase to closest 12m length or tons works fine.

Lapping & Bent of Bars & Mesh Fabric

Due allowance should be made of Lap & Bent of Bars and Lapping of Mesh Fabric. In general, minimum lap lengths is about 30 x Dia of bars, or allow 200 mm for fabric, 900 mm for straight bars and 150 mm for bent-up or hooks all measured per end/side. If you are purchasing the materials directly then you should make allowance for lap area and lengths. If you are doing cost estimate then the lapped areas or lengths can be ignored and the Net Area can be assumed as the unit rate for costing should include all these factors. To learn how to do costing estimates for rebars, click here

click to enlarge

 

 

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Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE, C.Eng) MEC Engineers, Civil & Structural Engineer HP: 016-8672189, Email: Widget: email cloaker