BBS for Circular RCC Column:
This article is about How to prepare bar bending schedule for Column
To preparing bar bending schedule for a column. there are some criteria & assumptions that require to be met Let’s get started.
Table of Contents
Forces on Column:
you should know the normal forces action on a column.
Just look at the diagram that is given below:
If you see the shear force and bending moment diagram, the column has less moments at center and more at bottom and top.
When bending moment is maximum not at any time tie a column at top & bottom every rime tie the column at center.
At site tie the bars at the height of 4 to 5 feet. The height of roof should not be more than 11 feet.
- Use less cutting of steel and provide desirable lapping.
- Lap another steels at same time.
- Overlap the top steels with bottom steels.
- Between the laps end to end spacing should be provided.
Bar Bending Schedule (BBS) used by:
Bar bending schedule is used by different kind of peoples and officials on construction site which is given below:
- Quantity surveyor
- Steel fixer
- Project manager
- Clerks of construction
In construction site all estimation and costing operation is the responsibilities of quantity surveyor. The bar bending schedule gives the details to quantity surveyor for finding out the number of steel its type, size and shape. Contractor are using bar bending schedule (BBS) for ordering the steel bar for proceeding the construction. Steel fixer using bar bending schedule (BBS) for doing their work or installing the bar in column, beam or slab according to the bar bending schedule (BBS) that how much cut length or bending of bar will be needed and which size of steel should be use. The inspector and clerks of construction refers to the BBS to make are that the reinforcement work in the field is in proper with the design reinforcement as per drawing.
BBS for Column:
Cross Section of Circular RCC Column
Detail of RCC Column
Details from the diagram:
- Thickness of slab is150 mm
- Floor height is 3 m or 3000 mm
- Footing depth is 400 mm
- Development Length is 50d
- Column has 8 numbers of 16 mm dia bars
- Stirrup spacing is 8mm @ 150 mm C/C
- Concrete Cover of Footing is 40 mm
- Concrete Cover of slab is 25 mm
Steps for BBS of Column:
Generally, there are five steps for preparing the bar bending schedule of column these five is given below:
- Find the length of Vertical Bar
- Find out lapping
- Cutting Length of Stirrups
- Number of Stirrups
- Bar Bending Schedule
Find the length of Vertical Bar:
Length of Vertical bar = Development length (Ld) + footing depth + Floor Heights + Slab Thicknesses + Overlap Length
= (12×16) +400+ (3000) +(150) +(50×16)
= 4734 mm or 4.73 m
Now we find the length of one vertical bar.
The total length of vertical bar = 4732 x number of steels in column
The total length of vertical bar = 4732 x 8
The total length of vertical bar = 37856 mm
Find out lapping:
length of lapping is 50d
Lapping length = 50 x Dia of steel
Length of lapping = 50×20 = 1000 mm.
We know that the length of typical steel is 12.25 m or 40 feet length
Total Length of Vertical Bar = 37.856 m that is more than 12.25 m or 40 feet so lapping should be provided.
Length of lapping is 1000 mm the result will be 37856 + 1 = 38.856 m
It is mentioned already in this article, consider the points while lapping the bar. There is no one right process we can use. Just remember the lines.
- Don’t tie a column at bottom and also at top
- Lap at another bars every time
- Overlap top bars with bottom bars always
Cutting Length of Stirrups:
we already discussed cut length of stirrup in Bar bending schedule of beam article.
Length of One Hook = 9d
Cutting length of Stirrup = (Perimeter of stirrup – concrete cover) + Number of Hooks
Cutting length of stirrup = (πd-cc) + (2 hooks)
Cutting length of stirrup = (3.14×450-25) +(2x9d)
= (1413-25) + (2×9×16)
= 1388 + 288
Cutting length of Stirrup = 1676 mm
Number of Stirrups:
Number of stirrups = (Total length of Column ÷ spacing of stirrups) +1
Number of stirrups = 4773 ÷ 150 + 1
Number of stirrups = 32.82 say 33 numbers
Bar Bending Schedule:
The bar bending schedule of column is shown below in table
|S. NO||Bar Mark||Bar dia||No of bars||Length (m)||unit weight(m/kg)||weight of steel (Kg)|
|Total Weight of Reinforced Concrete Column||116.02|
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You may also read:
- Types of Loads on Structure
- Important Thumb Rules used in Construction by Civil Engineers
- Standard Size of Column