Bar Bending Schedule
Bar bending schedule of Reinforced concrete structural members having comprehensive Terminologies and Reinforcement detailing
Description
In Reinforced concrete structural members, the steel rebars are used to overcome the tensile stresses as concrete has negligible tensile strength. In estimation, we just calculate the amount of steel required for specific line elements (beams and Columns) and plate elements (slabs) of reinforced concrete Structure. Structure Engineers not only calculates the amount of steel but also prepare a bar bending schedule. They also determine the Bars location (inline and plate elements), marking of bars ( to mark the bars according to the drawing details), size of bars ( length and diameter), the number of bars, cutting length, bend and shape of the bars which we called bar bending schedule (BBS).
From this article you can learn following details of bar bending schedule which are mentioned below;
1- Definition of bar bending schedule and its signification?
2- Associate terminologies in Bar bending schedule BBS
3- Drawing details of Reinforcement in Bar bending schedule of a beam (BBS)
Bar Bending Schedule and its Signification
The bar bending schedule is the calculation of steel in the Reinforced concrete structure. Then, locating the bars inappropriate location, marking the bars for drawing details, cutting the bars where it is required, deciding the type of bend and shape of the bars for any reinforced structural members.
Signification
When we construct to reinforce concrete structural members, so we provide the bars at different locations. There are a lot of bars which we offer at some angle. We also use some cutting bars; we also provide various bends in the bars. So, this bar bending schedule helps us a lot in reducing the duration of the project.
- They are labor who usually cut and bend the bars on the construction site. They cannot technically understand the drawing details of Reinforcement, so we provide the details of the bar bending schedule to overcome any inconvenience.
- In the construction site, the worker may cut down the steel from the wrong direction or having an inappropriate length. So, a bar bending schedule will help them determine the exact location of the cutting and bending of bars.
- For the site Engineer, it will be easy to guide the labors about the Reinforcement detailing.
BBS reduces the cost of steel due to reducing wastage of Reinforcement in cutting and bending, and also it will reduce the time by making the execution process faster.
Associate Terminologies in BBS
Hook length (stirrup cutting length)
Hook length is generally provided inline elements ( beam and column). It is offered to stirrups. In stirrups, hooks are usually provided at both ends of rebars.
Cutting length or hook length= 9d (d is the diameter of bars)
Cutting length of rectangular stirrups having hooks
Total cutting length or hook length of any stirrup or tie (for two hooks) = full length of rebar + 2× total hook length
If we consider that the total length of the bar is “L.”
Total cutting length = L+ 2 × 9D
Cranked length and bend length
The calculation of bend length differs from the estimate of cranked bar or bent up bar and the bends we provide at the corner.
Cranked length of the bar
Due to the shear stresses negative moment (hogging) produce, so to resist that moment we provide the bent-up bars which are called cranked bars.
Cranked bar in slab
Cranked bar in beams
Crank length = 0.42D
Where D is the height of rebar
D= Slab thickness – (Top cover +bottom cover) -bar diameter
Usually, bars are bent at 45o or 300
Cranked are mostly used in plate elements (slabs) sometime in beams. We also use cranked bars.
Bend length
It is length when we bend the column rebars to combine it with footing rebars. The extra bending length is considered as bend length.
Bend length = 16d
Development length in BBS
It is the length of bars which is provided for the transferring of stresses from steel to concrete. To embed the steel into concrete for increasing their bond strength, we need some extra quantity of length of steel.
Calculation of development length
Ø = nominal diameter of the bar
σs = Stress in steel bar where we consider the design load
τbd = Design stress
lap length
If the bar’s length is not sufficient to make it the adequately designed length, then we provide the lap between the bars. The length of the lap is called lap length. It is also called overlapping length as bars are overlapped with each other side by side.
Calculation of lap length
Different grade of concrete has different lap length.
For grade M20 concrete
For column= 45d
For beam= 60d
For slab= 60d
Unit weight of steel
It is the weight of steel which will be taken by the supplier.
The formula is W= D2L/162
D is the diameter of steel bar in mm
L is the length of bars in the meter
W is the weight of steel bar
Drawing Details of Reinforcement in BBS
Bent up Bar
additional length= 0.444h
total length = L + 0.44h
90o-Standard Hooks (ACI)
Total length = L + 18 db ; for R = 4db
180o-Standard Hooks (ACI)
Total length = L + 20db
Cross-section details of the beam are given below
h =375 – 2 *40 -2 *10 – 2(15/2) = 260
M2= 4000 + 2*228 – 2*40 + 2* (0.414*60) = 5092
Shear stirrups
a = 375 – 2 * 40 – 10 = 285mm
b = 228 – 2 * 40 – 10 = 138mm
Total length of S-1 = 2(138 +285 +18* 10) = 1206 mm
Bar Bending Schedule
Conclusion
The above article concludes that the bar bending schedule is essential to understand the drawings of Reinforcement in concrete structural members. Otherwise, it would be difficult to comprehend the Reinforcement detailing while making the bar bending schedule the terminologies and formulas should keep in mind. By making it, we can reduce the cost and time of the project, because cutting and bending of bars will be done in the factory by the manufacturer and the percentage of wastage of steel will reduce while working on the construction site.
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