How To Make BBS of Column in Details?

 

bbs of column
Column Cross Section of Building
Untitled
Top view of column section

Two type of load acts on column lateral load and axial load. When you will cut cross- section you will find six vertical bars. Out of which 4 is 25Ø and 2 is 16 Ø.

Floor to floor dimension is shown in figure above. Column clear length is 3m.

At top where column ends, there column outer reinforcement will go Ld (development length) distance in roof slab.

Ld= 50d, where d is dia of bar.

Column size= 300mm *600mm

Clear cover in column=40mm

Clear cover in footing=50mm

Clear cover in slab=30mm

Dia of Stirrup= 8mm

3
Considering column between two slab

Here column we have divided in two zone. Now L/6 from top and bottom of  is Zone A. Remaining at center there is Zone B. We always try column Lap always lie in Zone B not in Zone A. Because when load is applied on column moment is more at bottom in Zone A. So we avoid lap in Zone A. Spacing of Stirrup in Zone A is less than Zone B. See in figure above in L/6 portion spacing is 100c/c and in Zone B it is 150c/c.

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Vertical Bar Calculation:

Length of 20 Ø

= 300+ (1500-50-25-25)+600+200+(3000*4)+(175*3)+(50*20)-(2*2*20)+50*20

=16945 mm = 16.945 m>12m

Brief:

Length of 20 Ø = Ld+Footing depth – cover of footing- Main bar of footing- Bar of footing+depth upto ground floor+200+ Floor to Floor height*4+ (Slab thk *3)+ Development length- Two bend+ one lap

where Development length, Ld= 50d, Lap=50d, Bend=2d

Total no. of 20 Ø bar= 4

Total length of 20 Ø bar = 16.945 * 4= 67.78m

Length of 16 Ø

= 300+(1500-50-25)+600+200+(3000*4)+(!75*3)+(50*16)-(2*2*16)+(50*16)

 =16586 mm = 16.586 m

Total no. of 16 Ø bar= 2

Total length of 16 Ø bar = 16.586 * 2= 33.172 m

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Cutting Length of Vertical Bars:

4
Lapping detail M

 

5
Lapping detail S

Lap distance from center of column is 75 mm. Hence end to end distance of lap is 150mm.

For 20 Ø 

Part 1:  300+(1500-50-25-25)+600+200+(3000*2)+(175*2)+(1500-75)-1*2*20

              =10235 mm = 10.235 m

              where bend= 1*2*20, b’ = 1500-75= 1425mm

Part 2:  (1500+75+1000)+175+3000+1000-(1*2*d)

            = 6710 mm = 6.71m

             where a’ = 1500 +75+Ld= 1500+75+1000= 2575 mm

                         Ld = 50 * 20 = 1000mm

For 16 Ø 

Part 1 : 300+(1500-50-25)+600+200+b-bend

            = 300+ (1500-50-25)+600+200+2375-(1*2*16)

             =4868 mm or 4.868 m

           where b= 1500 + 75 + (50*16) = 2375 mm

Part 2 : a+ (175*3)+ (3000*3)+Ld- (1*2*16)

          =11718 mm = 11.718 m

         where a= 1500- 75 = 1425 mm

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Cutting Length of Stirrups

a= 600-40*2-8/2-8/2= 512mm

b= 300-40*2-8/2-8/2= 212mm

Cutting length=(2*a)+(2*b)+(2*10*d)-(5*2*d), where hook=2*10d and bend = 5*2d

=(2*512)+(2*212)+(2*10*8)-(5*2*8)

=1528 mm = 1.528 m

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No of Stirrups: = Length/ spacing+1

 

6

Part A = 2700/100 +1 =28 nos

Part B = 2000/150 -1=12 Nos*4 = 48 Nos

Part C = 1175/100+1= 13 Nos *3 = 39 Nos

Part D = (650-30)/100+1= 7 Nos

Total Nos = A+B+C+D =122 Nos

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