Bar Bending Schedule

 Introduction

Bar bending schedule is a means to calculate the exact quantity of reinforcements required in a structure. It is helpful for any concrete work to know exact amount of cement, aggregate or sand required for a structure. It is referred to as BBS in short form. It involves calculating development length, diameter of bars to be used, stirrups, cutting length, crank length, and many more. It is a process of cutting and bending reinforcement bars into desired shape and size as per structural drawing. These drawings are handed by structural engineers for various structural elements like footing, column, beam, slab, etc. and then handed over to contractors for the execution of the work at site by the labors. The contractor must understand in depth before portraying it to the labors. BBS is necessary to the contractor as it is important in bidding for tenders. All these works play an important role without which work can’t proceed.

Advantages
Some of the advantages of BBS are –

• Provides accurate information of reinforcements to be used in concrete structural members, as a result of which, total reinforcements required in a structure can be calculated.
• Provides good perception to the engineer as how much monitoring work will be required for implementing the BBS. Reduces extra efforts and saves time.
• With this, extra amount of reinforcements can be deducted from the estimation billing and cost can be reduced that will prove to be economical.
• Labors can get the idea of cutting bars beforehand and in this way lot of extra efforts to implement the work will be reduced.
• Project management will be easy and estimated time of completion will be more practical.
• It will help quality control in-charge to monitor the quality of work and point out the defects beforehand.
• Billing will be quick and easy and clients can get bills way before time. Any changes to be made will become possible without much hassle.
• Wastes at sites will be reduced as only that much quantity of reinforcements will be transported to the site as it has been mentioned in bills.
• When used Fe 500 instead of Fe 415, the cost will be reduced by approximately 10% which is beneficial to the client looking for cheaper alternative.

How to prepare?
Given below are the steps for preparation of BBS –

• Firstly, it is important to point out the amount of steel required for various structural members. This can be found out with the help of layout or drawings.
• Secondly, it is required to count the number of rebar having different shapes and it is to be noted down in the bar bending schedule.
• Next, the length of the reinforcement bars is calculated which is useful in quantity estimation.
• Then the unit weight of reinforcement bars is calculated for calculating the quantity or volume.
• Then the weight of particular shape of bar is calculated as follows:

Weight of Reinforcement Bar (Shape of Bar) = No of Bars X Length of Bars X Unit weight of Bar
This will give the total weight of specific shape bar in kilogram which is the SI unit.

• An excel sheet is prepared and at last summary is made which lists out the costs and quantities.

Precautions
It is important to keep in mind the following points as some mistakes are common in BBS which costs a lot of money to the clients. Some of them are –

• Often it is seen that number of bars are miscounted which effects the whole process so, this must be kept in mind.
• The dimensions taken from layouts or drawings must be accurate. It is often seen that the mistakes are made in recognizing the unit from the drawing and in this way, error in calculation occurs.
• Other elements like length is often miscalculated as extra length for cutting is sometimes missed by the engineers. So, it is another important criterion for accurate measurements and calculations.
• The bars must always be described as per storey wise starting from ground floor and then proceeding towards respective floors upwards.
• For each structural element, the bars must be grouped together. This should be like beams and columns for each floor and then proceed towards other floors. Same applies to other structural elements too.
• For cutting and bending purpose, separate A4 sheet is required so as to reduce confusions. Also, these should not be included in the drawings where details about reinforcements is provided.
• The bars must be ordered as per numerical order. This depicts a clearer vision to the contractor while understanding the contract.
• Welding is avoided at the bends so deductions must be made there.
• Commonly used reinforcements bar dimensions are – 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 28 mm, 32 mm, 36 mm, 40 mm. Whereas standard length of reinforcement bar is 12 m.
• Weight per length of reinforcement bar is given as D²/160 where D is the diameter of the reinforcement bar.
• Weight per bar is expressed as Weight of Bar per meter X Standard length of bar.

Conclusion
Bar bending schedule plays an important role in civil engineering and it is considered an important tool in building a structure. Any changes made in the bar bending schedule is accompanied by changes in contract regarding cost and project management. It directly links the project management and execution time in the field or site of construction. Any error in this will affect time, costs and manpower so it is advised to carefully calculate the quantity in order to avoid any mistakes in calculations. Also, it is advised to follow the respective country’s codes to avoid any confusion like in India it should be followed as per IS code and so every country will follow different formula and method.

References

• Civil Click, “Bar Bending Schedule”- https://www.civilclick.com/what-is-bar-bending-schedule/
• Dream Civil, “Bar Bending Schedule”- https://dreamcivil.com/bar-bending-schedule-bbs/
• Construction Civil Engineering, “Download BBS – Bar Bending Schedule”- http://constructioncivilengineering.com/download-bar-bending-schedule.html
• Civil Query, “(BBS) Preparation of Bar Bending Schedule and Its Advantages”- https://www.civilquery.com/bar-bending-schedule/
• Medium, “What is bar bending schedule? Advantages of the bar bending schedule”- https://medium.com/@GemEngserv/what-is-bar-bending-schedule-advantages-of-the-bar-bending-schedule-564283e31c9a