In every construction work, the owner wants to know the quantities of materials required for construction. During construction work first, we need to know the required quantities of materials in that construction work.
For this, there are 4 methods in Estimation to find out the quantities of materials.
1. Centerline method
In this method first, the centerline length of all walls in the building is measured and calculated. After that, the calculated centerline length is multiplied with the breadth and the depth or height of the respective item to get the quantities of materials (centerline length X breadth X depth).
For the different sections of walls in the buildings, the centerline method for each type shall be worked out separately. And at last add with others according to the nature of work.
This centreline method is quicker as well as accurate as other methods. But in the case of the unsymmetrical wall, this method is less effective over other methods to find out quantities. Since the calculation process is fast and easy so if we need the the the quantity required for any construction fast this method is very helpful.
From figure 1 and 2:
Here, the centerline length = 2 X (4.5+2.5) =14m
Total quantity of earthwork excavation = 14 X 0.8 X 0.6 = 6.72m³
2. Long and Short Wall method
In this long and short wall method, the longer wall in the building (generally in one direction) is considered as a long wall and the shorter or partition wall in a perpendicular direction of the long wall is considered as a short wall. The long wall is measure from out-to-out where the short wall is measured end-to-end. The length of a long wall and short wall are multiplied separately with the breadth and height of corresponding sides to get the quantity. At last, the quantity of a long wall and a short wall is added.
From above figure 1 and 2:
The length of a long wall = 5m
length of short wall = 2m (measured from inside end to end)
Quantity of earthwork excavation for longwall = 2(5×0.8×0.6) =4.8m³
Similarly, the quantity of earthwork excavation for short wall = 2(2×0.8×0.6) = 1.92m³
∴ The total Quantity of earthwork excavation = (4.8+1.92)m³ = 6.72m³
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3. Crossing method
The crossing method is the same as the centerline method but different in the calculation process to find the centerline length. In this method, first the overall perimeter of the building is calculated first and then four times the thickness of the wall is subtracted. After that, we get the centerline length of the building. In the case of an internal wall, walls are grouped separately to their sections and measured between the internal force of the main wall at that level. This is the most used method in civil engineering during estimating.
From above figure 1 and 2:
Overall perimeter = 2 x 5+2 x 3 =16m
Centerline length = (16-4 X 0.5)m =14m
∴Total quantity of earthwork excavation = 14 X 0.8 X 0.6 =6.72m³
4. Bay method
This method of quantities measurements is generally used when the buildings have several bays. When are building the structure having a similar dimension this method for the find out quantities of materials is fast and easy in the calculation process.
For example, we have to build a 10 classroom of the same dimension. Then the cost of the one classroom is worked out and then multiplies by the number of bays in that building. The extra cost of the end walls and different framing if there is any, should be made.
Also Read: Standard measurement methods to calculate building construction works