Preparation of Bar Bending Schedule For Floor Slabs

Bar bending schedule is an important structural working document that shows the disposition, bending shape, total length, and quantity of all the reinforcements that have been provided in a structural drawing. It is often provided in a separate sheet (usually A4 paper) from the structural drawing. The bar marks from structural detailing drawing are directly transferred to the bar bending schedule. We normally quantify reinforcements based on their total mass in tonnes or kilograms. For smaller projects, you can quantify based on the number of lengths needed.

Bar bending schedule is prepared for floor slabs to show the quantity, size, and shape of rebars needed during the construction. This document is very important for pre-contract and post-contract operations. The information needed for the preparation of bar bending schedule for floor slab is picked from the reinforcement detailing drawings. One important parameter in the preparation of bar bending schedule is the quantity of steel required (in kilograms or tonnes). This is based on the unit mass and size of the rebars.

Unit mass of rebars
The unit mass of the reinforcements are derived from the density of steel. The density of steel normally used for this purpose is 7850 kg/m³.

For example, let us consider 12mm bar;
The area is given by (πd²)/4 = (π × 12²)/4 = 113.097mm² = 0.0001131m²
Considering a unit length of the bar, we can verify that the volume of a metre length of the bar is 0.0001131m³;

Density = Mass/Volume = 7850 kg/m³ = Mass/0.0001131
Therefore, the unit mass of 12mm bar = 7850 × 0.0001131 = 0.888 kg/m

Therefore for any diameter of bar;
Basic weight = 0.00785 kg/mm² per metre
Weight per metre = 0.006165 ϕ² kg
Weight per mm² at spacing s(mm) = 6.165ϕ²/s kg

Where;
ϕ = diameter of bar in millimetres

The unit weight of different types of reinforcement sizes is given in the Table below;

Diameter of bar (mm)	Weight per metre (kg)	Length per tonne (m)
6	0.222	4505
8	0.395	2532
10	0.616	1623
12	0.888	1126
16	1.579	633
20	2.466	406
25	3.854	259
32	6.313	158
40	9.864	101

Basic Shapes for Bar Bending Schedule

There are some basic shape codes in the code of practice (BS 8666:2005). But these days, it is common to sketch the bending shape on the BBS document to avoid the confusion and extra effort that comes with extracting the shape from a standard document.

To obtain the length of reinforcement bars in a structural drawing, use the following relation;

Length of bar = Effective Length + Width of Support – Concrete cover (s) – Tolerances

The typical values of tolerances (deductions) are given in the table below;

Example on the Preparation of the Bar Bending Schedule of a Slab

To illustrate how this is done, consider the general arrangement of the first floor of a building as shown below;

Bar Bending Schedule Calculations

Cutting Length of reinforcement = A + B + C – r – 2d (Table 2.19, Reynolds, Steedman, and Threlfall, 2008)

Where;
r = radius of bend (r = 24 mm for high yield 12 mm bars; and 20 mm for Y10mm bars)
d = diameter of bar

Bar Mark 01:
A  = 4000 + 230 – 35 = 4195 mm
B = 150 – 2(25) – 10 = 90 mm (including 10 mm tolerance)
C = 230 + 800 – 35  = 995 mm (from detailing considerations 0.2L)
r = 24 (for 12 mm bars)

L = A + B + C – r – 2d = 4195 + 90 + 995 – 24 – 2(12) = 5235 mm

Bar Mark 02:
L = 2230 mm

Bar Mark 03:
A  = 3600 + 230 – 35 = 3795 mm
B = 150 – 2(25) – 12 – 10 = 78 mm (including 10 mm tolerance)
C = 230 + 720 – 35  = 915 mm (from detailing considerations 0.2L)
r = 24 (for 12 mm bars)

L = A + B + C – r – 2d = 3795 + 78 + 915 – 24 – 2(12) = 4740 mm

Bar Mark 04:
A  = 1080 + 1200 + 230 – 25 = 2485 mm
B = 150 – 2(25) – 10 = 90 mm (including 10 mm tolerance)
C = 1200 + 230 – 25 = 1405 mm (from detailing considerations 0.2L)
r = 24 (for 12 mm bars)

L = A + B + C – r – 2d = 2485 + 1405 + 90 – 24 – 2(12) = 3932 mm

Bar Mark 05:
A  = 6000 + 230 – 35 = 6195 mm
B = 150 – 2(25) – 12 – 10 = 78 mm (including 10 mm tolerance)
C = 1200 + 230 – 35 = 1395 mm (from detailing considerations 0.2L)
r = 20 (for 10 mm bars)

L = A + B + C – r – 2d = 6195 + 1395 + 78 – 20 – 2(10) = 7628 mm

Bar Mark 06:
L = 4630 mm

Bar Mark 07:

L = 3830 mm

Bar Mark 08:
A  = 1200 + 230 – 35 – 25 – (15) = 1355 mm (including 15 mm tolerance)
B = 150 – 2(25) – 10 = 90 mm (including 10 mm tolerance)
r = 24 (for 12 mm bars)

L = 2(A) + 2(B) + C + D – 3r – 6d = 2(1355) + 2(90) + 2(125) – 3(24)  – 6(12) = 2996 mm

Bar Mark 09:
L = 2030 mm

Bar Mark 10:
L = 1830 mm

The final table for the bar bending schedule can be prepared as shown below. However, it is important to include all details in the schedule to avoid confusion.

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