Bar Bending Schedule (BBS)
Bar bending schedule is a table form data in which various diameters of steel, the shape of bending, length of each bent and straight portions, angles of bending, the total length of each bar, and a number of each type of bar. This information is very useful for site engineer who is working on-site and while preparing estimate and bills of work.
How Is Bend Deducted In Bar Bending Schedules?
The Bend deductions are very much important while calculating the Bar Bending Schedule. Basically, we will be having a thought that while bending a bar how much length of the bar should be cut.
Many of us think that we require more than the required length so that the bar will come to its perfect length after Bending. But this is not true.
The Reinforcement bars which come to the market are of Length 12 m.
So as the steel has the deformation property, due to the elasticity the length of the bar increases while we bend them.
So the Deductions will be different for the different bents based on the angles.
The Deductions are as follows:
d is the diameter of the bar.
1. For a 45-degree bend, the deduction is d.
For example, if the length of the bar is 12 m (assume), the diameter is 25 mm. So for one bend, it is deducted by d.
Cutting Length = 12- d= 12- 0.025= 11.975 m.
Therefore only 11.975 m bar is necessary to get a bar of Length 12 m after bending.
If we bend a bar of 12 m then the length of the bar after bent will be
= 12+ d= 12+0.025= 12.025 m which will be more than required.
2. Similarly for a 90-degree bend, the deduction is 2d.
For example, if the length of the bar is 12 m (assume), the diameter is 25 mm. So for one bend, it is deducted by 2d as it is 90 degrees bend.
Cutting Length = 12- 2d= 12- 2*0.025= 11.95 m.
3. Similarly for 135-degree bend, the deduction is 3d.
For example, if the length of the bar is 12 m (assume), the diameter is 25 mm. So for one bend, it is deducted by 3d as it is 135 degrees bend.
Cutting Length = 12- 3d= 12- 3*0.025= 11.925 m.
4. Similarly for a 180-degree bend, the deduction is 4d.
For example, if the length of the bar is 12 m (assume), the diameter is 25 mm. So for one bend, it is deducted by 4d as it is 180 degrees bend
Cutting Length = 12- 3d= 12- 4*0.025= 11.900 m.
Note: For n number of bends there should be n deductions in the original length to get the cutting length.
Length=12m, Diameter=25mm, bent angle= 90 degree & no of bents are 2.
Therefore Cutting Length= 12- 2*(2d)= 12- 2(2*0.025)= 11.9 m.
Note: Practically in the construction site we will be deducting only 2d for a single bend irrespective of the angle (i.e. even though the angles are 45 degrees, 90 degrees,135 degrees, 180 degrees we will deduct only 2d for each bent).
Refer to “IS:2502 Code of Practice for Bending and Fixing of bars” for further information.
Read More: Steel Quantity Calculation Excel Sheet
How to Prepare Bar Bending Schedule
Let’s take the example of RCC slab reinforcement to calculate and prepare Bar Bending Schedule.
RCC Slab Reinforcement Details
- Main Bent Up Bars = 12 mm Dia. @ 150 c/c
- Distribution Steel Bars = 8 mm Dia. @ 180 c/c
- Side Cover = 50 mm
- Top & Bottom Cover = 20 mm
- All Hook’s = 90 Degree
- Bent Up = 45 Degree
|1||12 mm dia main Steel bars |
@ 150 mm c/c Alternate
|L = Span Length + Wall Width(Right) + Wall Width (Left) + 2 x 9D (Hooks) – 2xCover|
L = 3 + 0.23 + 0.23 +
(2 x 9 x 0.012) – (2 x 0.05)
|L = 3.58 m (Straight length without bent)|
|Span = 4 + 0.23 + 0.23 – (2 x 0.05)|
= 4.36 m
|No. of Bars = (4.36/0.15) + 1 = 30 nos.|
|Extra Length of Bent up:|
|X – Value|
|Extra Length = 0.45 X|
|X = 0.12(Slab Thickness) – 2 x 0.02 (Top & Bottom Cover) – 0.012/2(Harf dia top) – 0.012/2( Half dia bottom)|
|L = 3.58 + 0.45X|
L = 3.58 + 0.45 x 0.068
L = 3.61 m
|(Note: In case of bent up bars are provided on both sides, we have to add 0.45 X twice in length)|
|8 mm dia. Distribution steel @ 180 mm c/c|
|Bars at Bottom:|
| Hook Length = 9d|
= 9 x 0.008
= 0.072 < 0.075
( Mini. Hook length = 0.075)
|L = 4 + 0.23 + 0.23 + 2 x 0.075(Both side hook(9d)|
|L = 4.51 m|
|Width of Slab = 3 + 0.23 + 0.23 – 2 x 0.05 (Both Side Cover) |
= 3.36 m
|No. of Bars = (3.36 / 0.18) + 1 |
= 20 nos.
|Bars at Top:|
|Width of Slab at one end for bent up at Top|
|L= 0.23 + 0.45 – 0.068 – 0.05(cover)|
|L = 0.562 m|
|Nos. of Bars at one End:|
= (0.562/0.18) + 1
= 5 nos.
|Nos. of bars at both side |
= 2 x 5 = 10
|Total Bars = 20 + 10 =30||30||4.51||@||0.40||54.12 kg|
Advantages of Bar Bending Schedule (BBS)
1. When Bar bending schedule is available, cutting and bending of reinforcement can be done at the factory and transported to the site. This increases faster execution at the site and reduces construction time and cost due to less requirement of workers for bar bending. Bar bending also avoids the wastage of steel reinforcement (5 to 10%) and thus saves project costs.
2. Using a bar bending schedule when used for Fe500, saves 10% more steel reinforcement compared to fe415.
3. It improves the quality control at the site as reinforcement is provided as per bar bending schedule which is prepared using the provisions of respective detailing standard codes.
4. It provides a better estimation of reinforcement steel requirement for each and every structural member which can be used to compute overall reinforcement requirement for the entire project.
5. It provides better stock management for reinforcement. Steel requirement for the next phase of construction can be estimated with accuracy and procurement can be done. This prevents the stocking of extra steel reinforcement at the site for a longer time, preventing corrosion of reinforcement in the case of coastal areas. It also prevents a shortage of reinforcement for ongoing work by accurate estimation and thus concrete construction works can proceed smoothly.
6. Bar bending schedule is very much useful during auditing of reinforcement and provides checks on theft and pilferage.
7. Bar bending schedule can be used for reinforcement cutting, bending, and making a skeleton of a structural member before it can be placed at the required position. Other activities such as excavation, PCC, etc can proceed parallel with this activity. So, overall project activity management becomes easy and reduces the time of construction. It becomes helpful in preventing any damages due to construction time overrun.
8. It provides benchmarks for quantity and quality requirements for reinforcement and concrete works.
9. Bar bending schedule provides the steel quantity requirement much accurately and thus provides an option to optimize the design in case of cost overrun.
10. It becomes easy for site engineers to verify and approve the bar bending and cutting length during inspection before placement of concrete with the use of bar bending schedule and helps in better quality control.
11. It enables easy and fast preparation of bills of construction works for clients and contractors.
12. The quantity of reinforcement to be used is calculated using engineering formulas and standard codes, so there is no option for approximate estimation of steel reinforcement.
13. With the use of bar bending schedule, mechanization of cutting and bending of reinforcement can be done, again reducing the cost and time of project and dependency on skilled labor requirement. It also improves the reliability of the accuracy of bar cutting and bending.
14. When mechanized bar cutting and bending is used, the cost of reinforced concrete work per unit reduces and helps in cost optimization of construction projects.
What Is Bar Bending Schedule?
Bar bending schedule is a table form data in which various diameters of steel, the shape of bending, length of each bent and straight portions, angles of bending, the total length of each bar, and a number of each type of bar.
Bar bending is a table form data in which various diameters of steel, the shape of bending, length of each bent and straight portions, angles of bending, the total length of each bar, and a number of each type of bar.
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