Details of bar bending schedule for column
In this construction article, you will learn step-by-step guidelines for generating bar bending schedule for column.
The following points should be noted prior to create bar bending schedule for column.
Since, the column contains maximum moments at top and bottom and less at centre, therefore, a column should not be joined at top & bottom where the critical moment is extreme. The column should be joined at centre.
Never join a column at top & bottom where the critical moment is high. Always join the column at centre.
It is always recommended to join the bars at 5 feet height as each roof should not be in excess of 10 feet. In this regard, the following points should be considered :-
• Curtail the cutting of bar and lapping frequently.
• Always lap alternate bars simultaneously.
• Always overlap top bars with bottom bars.
• Retain adequate end to end spacing among the laps.
Assume the dimensions of the column as follow :-
• Slab Thickness – 125 mm & 100 mm
• Floor height – 3000 mm or 3 m
• Ground Floor Level – 3300 mm
• Footing Height – 300 mm
• Development Length – 50d
• Column has 6 numbers of 20 mm dia bars
• 8mm stirrups @ 150 mm C/C
• Footing Clear Cover – 40 mm
• Slab Clear Cover – 25 mm
Step 1 – Determine the length of Vertical Bar
Length of Vertical bar = Development length (Ld) + Height of Ground Level + Floor Heights (1,2,3)+ Slab Thicknesses + Overlap Length (Det.B)
= (50×20)+3300+ (3×3000)+(3×125)+100 +(50×20)
= 14775 mm or 14.78 m
The length of one vertical bar is known. Generally, the reinforcement drawings of column will not be available with lapping details.
Step 2 – Determine lapping
Since, the necessary lapping length is 50d = 50 * Diameter of the bar = 50×20 = 1000 mm.
Suppose, every bar is 12.25 m or 40 feet length (approx).
Total Length of Vertical Bar = 14.2 m that is in excess of 12.25 m so each rod will be lapped minimum one time to obtain the desired length.
There, the lapping length is included with the total length = 14775+1000 = 15775 mm or 15.78 m
Step 3 – Cutting Length of Stirrups
Length of One Hook = 9d (According to Estimating and Costing in Civil Engineering P.No.214)
Cutting length of Stirrup = Perimeter of stirrup + Number of Bends + Number of Hooks
= 2(a+b) + 3 numbers of 90 degree bends + 2 numbers of hooks
= 2(500+200)+(3 x2d)+(2x9d)= 2×700+3x2x20+2x9x20
Cutting length of Stirrup = 1880 mm
Step 4 – Number of Stirrups
Number of stirrups essential = (Total length of Column/spacing of stirrups)+1
= (3300+125+3000+125+3000+125+3000+100)/150 + 1
Number of stirrups = 85 no.s
Step 5 – Bar Bending Schedule
Diameter of Bar - 20 mm
Numbers – 6
Cutting Length – 14.2 m
Total Length- 85.2 m
Diameter of Bar - 8 mm
Numbers – 85
Cutting Length – 1.88 m
Total Length- 159.8 m