Let us make a footing of size 1.5 ft × 1.5 ft. having 10" ( 0.833 ft. ) thickness as shown in the drawing.
Given data :
footing length = 1.5 ft., width = 1.5 ft. , thickness = 0.833 ft.
rebar diameter = 10 mm.(0.0328 ft.), spacing =5" (0.416 ft. ) c/c, cover = 2"(0.166 ft ) on all the sides.
From part 1, the number of footings = 14nos.
4a. The volume of footing for the compound wall
= total nos. × length × breadth × thickness
= 14 nos. × 1.5 ft. × 1.5 ft. × 0.833 ft.
=26.24 cu ft.i.e.0.743 cum.
4b. BBS for the footings:
No. of bars along x-axis
= [ {( footing length ) - ( 2 × cover )} ÷ spacing ] + 1
= [ {( 1.5 ft.) - ( 2 ×0.166 ft.)} ÷ 0.416 ft.] +1
= [ { 1.168 ft. } ÷ 0.416 ft. ] +1
= 2.807 +1
= 4 nos.
( by rounding off )
No. of bars along y-axis
= [ {( footing width ) - ( 2 × cover )} ÷ spacing ] + 1
= [ {( 1.5 ft.) - ( 2 ×0.166 ft.)} ÷ 0.416 ft.] +1
= [ { 1.168 ft. } ÷ 0.416 ft. ] +1
= 2.807 +1
= 4 nos.
( by rounding off )
Cutting length of the bar along the x-axis
= [ {bar length in x - axis } +{ 2 nos. ×( L- bend length)}] - 2nos.× ( 2 times bar dia. for 90° bend.)
( we have deducted 2 times bar dia i.e. 2d for the 90° bend of the bar. )
=[ { footing length - 2 × cover } + 2nos.×{ footing height - 2 × cover}] - 2× ( 2 × bar dia. )
= [ { 1.5 ft. - 2 × 0.166 ft. } + 2 × { 0.833 ft. - 2 × 0.166 ft. } ] - 2 × ( 2 × 0.0328 ft.)
= [ 1.168 ft. + 1.002 ft. ] - 0.131ft.
= 2.17 ft. - 0.131 ft.
= 2.039 ft. i.e. 0.6214 m.
Cutting length of the bar along the y -axis
= [ {bar length in y - axis } +{ 2 nos. ×( L- bend length)}] - 2nos.× ( 2 times bar dia. for 90° bend.)
=[ { footing width - 2 × cover } + 2nos.×{ footing height - 2 × cover}] - 2× ( 2 × bar dia. )
= [ { 1.5 ft. - 2 × 0.166 ft. } + 2 × { 0.833 ft. - 2 × 0.166 ft. } ] - 2 × ( 2 × 0.0328 ft.)
= [ 1.168 ft. + 1.002 ft. ] - 0.131ft.
= 2.17 ft. - 0.131 ft.
= 2.039 ft. i.e. 0.6214 m.
Note: The cutting length & number of bars in both ( x & y ) directions will be the same, in the case of square footing having a similar bar diameter.
Now, we will prepare BBS of the footing, from calculated data.
1. x- axis 10 4 0.6214 2.4856 0.62 1.54
2. y - axis 10 4 0.6214 2.4856 0.62 1.54
Total weight of the bars = 3.08kgs
Add 2 % wastage = 0.0616kgs
A grand total of rebar for a footing = 3.1416 kgs.
Note : Weight of 10mm dia bar /meter is 0.62 kg.
The total weight of the 10mm bar for all the footings
= 14 nos. × 3.1416 kgs
= 43.98 kgs.
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