Deduction Rules For Brick Masonry In Arch
The following types of deduction should be provided in arch construction :-
- Rectangular Openings
- Segmental Arch Openings
- Semi-circular arch opening
- Masonry of arch
- Lintel over opening
For rectangular opening, full deduction should be provided.
Deduction = Length x Height x Thickness of wall = L x H x Thickness of wall
Segmental Arch Openings
If there exist a segmental arch opening over the rectangular opening, deduction in masonry should be provided for both the rectangular opening & the segmental arch opening.
Area of rectangular section = Length x Height = L x H
Area of segmental section = 2/3L x R + R3/2L
So, the total deduction should be as follow :-
[L x H + 2/3L x R] x thickness of wall
Semi Circular Arch Opening
Area of semi-circular section = πR2/2
But the approximate area of the semi-circular section = 3/4 L x R
So, the total deduction = [L x H + 3/4 L x R] x thickness of wall.
Masonry Of Arch
The quantity of masonry in arch is calculated in cubic metre as a individual item.
The quantity of arch masonry is subtracted from the total masonry.
Masonry of arch = Centre length of arch x breadth of the arch x thickness of arch
So, the deduction for arch in masonry = Lm x b x t
Lintel over opening
An RCC lintel is arranged over the door/window opening.
The quantity of RCC in lintel is subtracted from the masonry work.
A bearing of 10 to 15cm from the edge of opening is arranged to the lintel on either end of the opening.
So, the length of lintel will be as follow :-
Length of lintel (L) = Span of opening + 2 x bearing deduction for lintel = L x width of wall x thickness of lintel.