First of all, there are some criteria & assumptions that need to be met while making bar bending schedule for a column.
Loads Acting on Column
We hope that you know the typical load action on a column.
Just take a look at the below diagram.
If you see the internal forces and moment diagram, the column has maximum moments at top and bottom and less at centre.
Never tie a column at top & bottom where the critical moment is high. Always tie the column at centre.
For practical always tie the bars at 5 feet height. Since every roof should not be more than 10 feet.
· Minimise the cutting of bar and lapping as often as possible.
· Always lap alternate bars at a time.
· Always overlap top bars with bottom bars.
· Maintain sufficient end to end spacing between the laps.
Bar Bending Schedule for Column
From the diagram,
· 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 – Find 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
Now we know the length of one vertical bar. Normally column reinforcement drawings won’t come with lapping details.
Step 2 – Find out lapping
As we know that lapping length required is 50d = 50 * Diameter of the bar = 50×20 = 1000 mm.
We know that each bar is 12.25 m or 40 feet length (approx).
Total Length of Vertical Bar = 14.2 m which is more than 12.25 m so each rod will be lapped at least once to attain the required length.
So we have added the lapping length with the total length = 14775+1000 = 15775 mm or 15.78 m
As we mentioned earlier in this post, consider the points while lapping the bar. There is no one correct method we can use. Just remember the lines.
· Never tie a column at top & bottom
· Always lap at alternate bars
· Always overlap top bars with bottom bars
Step 3 – Cutting Length of Stirrups
Length of One Hook = 9d (As per 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 required = (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 | Numbers | Cutting Length | Total Length | |
Vertical bar | 20 mm | 6 | 14.2 m | 85.2 m |
Stirrups Bar | 8 mm | 85 | 1.88 m | 159.8 m |
