Civil Engineering Department

TOPIC –BBS For Column – Important Notes

SEMESTER-6^TH

BY

Mrs. MANDAKINI MOHANTA / MR BIKASH DAS

(LAB ASST. civil eNgineering department)

AY:2021-2022

BBS For Column – Important Notes

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Ensure to follow the below rules while bar bending for column

• Always tie the column at the centre of each floor Since the axial loads & internal forces are maxim at top & bottom of the column.
• Always lap alternate bars
• Always lap top bar over the bottom bar
• Try to minimize the lap length and cutting of the bar as much as you can

Given Data

• Slab Thickness – 175 mm & 125 mm
• Floor height – 2750 mm
• Basement height – 650 mm
• Footing height – 1200 mm
• Footing Development Length – 250 mm
• Column Size – 600 x 300 mm
• Column Cover – 40 mm on each side
• Column Reinforcement – 6 nos of 16mm dia
• Stirrups – 8 mm of 200 c/c
• Ld = 50d (assumption)

Step 1 – Find the total length of vertical bar height

Vertical Bar Length = Footing Development Length + Footing height + basement height + Height of all floors + Slab thickness of all floors + Development length at the end of the column top 

Vertical Bar Length = 250+(1200-30-25-20)+650+(4*2750)+(175+150+150+125+125)+50d

= 13750+(50*16)= 14550 mm or 14.55 m

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Step 2 – Find Lap Length of Column Reinforcement

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As you know the steel comes at a predetermined length of 12.25 m or 40 feet. From the above calculations, we know that we have to lap the column at least once in order to attain the height.

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Assuming, Lap Length of column reinforcement as 40d

Lap Length = 40d = 40*16 = 640 mm or 0.64m

Total Vertical Reinforcement = 14550+640 = 15190 mm or 15.19m

Step 3 – Find Number of Stirrups

Number of Stirrups = (Total Vertical Bar Height / Spacing) + 1

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Total Vertical Bar Height = Footing height + basement height + Height of all floors + Slab thickness of all floors

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= (1200-30-25-20)+650+(4*2750)+(175+150+150+125+125) = 13500

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Number of Stirrups = (13500/200)+1 = 68.5 or 69 Nos

Step 4 – Find Cutting Length of Stirrups

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Cutting Length of Stirrups = Perimeter of Stirrup + 2 hook length – 3 * 90° bends – 2 * 135° bends

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= 2(520+220)+(2*9d)-(3*2d) – (2*3d) = (2*740)+(2*9*16)-(3*2*16)-(2*3*16)=1576 mm

Step 5 – Bar Bending Schedule – Column Format

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