Bar bending schedule (BBS) of a storm water drain. / Calculating the cutting length & weight of reinforcement in a storm water drain.

 Let us make BBS of the stormwater drain as shown below.

Given data:

RCC pardi depth = 450mm.

RCC pardi width = 150mm.

Drain bed width = 850mm.

Drain bed thickness = 150mm.

Stormdrain length = 8m.

Clear cover = 50mm.

Calculation:

A. Cutting length:

Given data:

Drain pardi vertical reinforcement     = T10 @ 200c/c

Drain pardi horizontal reinforcement = T8 @ 175c/c.

Drain bed reinforcement-1= T10 @ 150c/c.

Drain bed reinforcement-2 = T8 @ 175c/c.

1. Drain pardi vertical reinforcement:

a. Cutting length of outer vertical reinforcement

= [ {a } + {b} + {c } + {d } - (2nos.× 90° bend)]

= [{pardi width -(2nos.× cover)} + {(pardi depth - cover) + (bed thickness -cover- bed reinforcements )}+ {pardi width  -cover} + {175mm.} - ( 2nos. × 2d)]

= [{150mm. -(2nos.× 50mm.)} + {(450mm. - 50mm.) + (150mm. - 50mm.-10mm.-8mm. ) }+ {150mm. -50mm.} + {175mm.} - ( 2nos. × 2 × 10mm. )]

= [{50mm.} + {482mm.} + {100mm.} + {175mm.} - (40mm.)]

= 767mm.

= 0.767m.

b.  Inner vertical reinforcement 

 Cutting length of inner vertical reinforcement

=  [ {a } + {b} + {c } + {d } - {2nos.× 90° bend}]

= [{pardi width -(2nos.× cover)} + {(pardi depth - cover) + (cover + top bed reinforcements )}+ {cover} + {175mm.} - {2nos. × 2d}]

= [{150mm. -(2nos.× 50mm.)} + {(450mm - 50mm.) + (50mm + 10mm. +8mm. )}+ {50mm.} + {175mm.} - {2nos. × 2 × 10mm.}]

= [{50mm.} + {468mm.} + {50mm.} + { 175mm.} - {40mm.}]

= 703mm.

= 0.703m.

2. Drain pardi horizontal reinforcement:

 Cutting length of horizontal reinforcement

= [ drain length - (2nos. × cover)]

= [ 8000mm. - ( 2nos. × 50mm.)]

= 7900mm.

=7.9m.

3. Drain bed reinforcement -1:

Cutting length of bed reinforcement-1 

= horizontal reinforcement of pardi = 7900mm.= 7.9m.

4. Drain bed reinforcement -2:

Cutting length of bed reinforcement -2

= [{2nos. × a} + {b} - {2nos. × 90° bend}]

= [{ 2nos.×( bed thickness - 2nos. × cover)} + {bed width - 2nos. × cover} -{2nos. × 2d}]

= [{ 2nos.× ( 150mm. - 2nos. × 50mm.)} + {850mm. - 2nos. × 50mm.} -{2nos. × 2 × 8mm.}]

= [ { 100mm.} + {750mm.} - {32mm.}]

= 818mm. = 0.818m.

Note: Cutting length of top & bottom reinforcement -2 is equal.

B. No. of bars:

1. No of drain pardi vertical bar

= [(drain length - 2nos. × cover) ÷ c/c distance] +1

= [8000mm. - 2nos. × 50mm.) ÷ 200mm.] +1

= 39.5 +1

= 40.5

By rounding off = 41nos.

2. No of drain pardi horizontal bar

= [(pardi depth - cover) ÷ c/c distance] +1 

=  [(450mm. - 50mm.) ÷ 175mm.] +1 

= 2.28 +1

= 3.28nos.

By rounding off = 4nos.

3. No of drain bed bar-1

 =  [(bed width - 2nos. × cover) ÷ c/c distance] +1 

 = [(850mm. - 2nos. × 50mm.) ÷ 150] +1 

= 5+1

= 6nos.

4. No of drain bed bar-2

 =  [(drain length - 2nos. × cover) ÷ c/c distance] +1 

 = [(8000mm. - 2nos. × 50mm.) ÷ 175] +1 

= 45.14+1

= 46.14

By rounding off = 47nos.

Total no. of bed bar-2 for top & bottom

= [2sides × 47nos.]

= 94nos.

Now, let us prepare a BBS table for the stormwater drain.

Sl. No.	Type of Bar	Dia. in mm.	Nos.	Length in m.	Total length in m.	Weight in Kg/m.	Total  bar wt. in kg.
1.	Drain pardi vertical bar.
a.	Outer bar.	10	41	0.767	31.447	0.612	19.24
b.	Inner bar.	10	41	0.703	28.823	0.612	17.64
2.	Drain pardi horizontal bar	8	4	7.90	31.60	0.395	12.48
3.	Drain bed Bar-1	10	6	7.90	47.4	0.612	29.00
4.	Drain bed Bar-2	8	94	0.818	76.89	0.395	30.37
5.	Total weight of bars =						108.73
6.	Add 3% wastage =						3.26
7.	The grand total wt. of rebar's =						112.00

 

Note:

1. The depth of the stormwater drain varies according to the road level & slope. But to understand the calculation, a constant value is taken. 

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Thank you for going through these calculation steps❤. Have a good day 😄.

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