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Sunday, August 13, 2017

Preparation of Bar Bending Schedule For Floor Slabs


Introduction
Bar bending schedule is an important structural working document that rightly gives 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 length needed.


Unit mass of rebars
The unit mass of the reinforcements are derived from the density of steel. The density of steel normally adopted 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

Knowing full well that;

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


Bending Shapes
There are some basic standard shapes that have definite shape codes in the code of practice. But these days, it is better to sketch the bending shape on the document to avoid the confusion that concerns the exact document the shape code was picked from. Ideally, all these information ought to be provided in the document.

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





The design produced the floor slab detailing shown below;



                                 SECTION A-A

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 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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7 comments:

  1. Dear UBANI, I looked ur rebar details. Which code? European
    or American codes and practices?.. Normally bottom bars shown with dashed lines.Some of the bottom bars in general half of them used as bent up.Good luck..

    ReplyDelete
    Replies
    1. Top reinforcements are represented with dashed lines, while bottom reinforcements are represented with continuous lines.

      Delete
    2. See BS EN ISO 3766:2003 Table 1 (No. 16) It explains what Ubani Ranks says.

      Delete
    3. Actually BS EN ISO 3766:2003 Table 1 (No. 16) says Top Reinforcement is represented with continuous lines while the bottom reinforcement is presented with Extra wide dash lines whenever bottom and top reinforcement is presented on the same drawing.

      Delete
  2. You did well explaining these things. It seems so easy here till one gets to the field and begin to sweat but with this explanation, any one can grab it

    ReplyDelete
  3. This is apt and interesting.
    Now it'll be easy to do some preparation before these thieves come and begin to spill trash.

    Thank you for these wonderful tips dear

    ReplyDelete
  4. Excellent tutorial,informative and easy to read.

    In plan, dwg shows section looking west. In section dwg shown looking East.

    British standards shows bottom reinforcement presented with dashed lines whenever bottom and top reinforcement is presented on the same drawing.

    ReplyDelete