When there are number of junctions in a building, for every junction special consideration shall have to be made to find the correct quantity. For each junction half breadth of the respective item or footing is to be deducted from the Centre line length. For building having different types of walls each set of wall shall have to deal separately.
Following points should be kept in mind while using centre line method -
(1) The term junction is used to indicate the meeting points of cross walls with main walls. For one cross wall, there are two junctions and so on, refer fig.
Total centre line length = (2 X 5.30 +2 X 3.40 + 3.40)
= 10.60 + 6.80 + 3.40
= 20.80 m
Net centre line length = Total centre line length - (1/2 X width X number of junction)
= 20.80 - (1/2 X 0.30) X 2 = 20.80 - 0.30
=20.50 m
(2) Centre Line lengths are to be calculated with great care where walls with different thickness meet.
Centre line length of 300mm walls = (2 X 5.30 + 2 X 3.40) = 17.40 m
Centre line length of 200mm wall
= 17.40 - (1/2 X 0.20 X 2)
= 17.20 m
(3) When to cross walls are meeting the main walls as shown in figure then Centre line length of walls are calculated As given below:
Centre Line length of 300 mm wall = ( 2 X 6.00 + 2 X 4.00)
= 20.00 m
Number of junctions 300 and 300 mm walls= 4
Number of junctions 200 and 200 mm walls = 2
Centre Line length of 200 mm wall =
( 2 X 2.00 + 6.00) - [ ( 1/2 X 4 X 0.30) + ( 1/2 X 2 X 0.20)]
= 10.00 - ( 0.6 + 0.2)
= 9.20
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