Detailed estimate is prepared to calculate the quantities of various items of work for civil engineering structures. For preparing this, drawing and specifications of items is required. In this chapter step-by-step procedure for preparing the detailed estimate is explained with the help of suitable example.
4.1.1 Procedure for Taking out Quantities for Various Items of Works by P.W.D. and IS 1200
For preparing the estimate and costing, it is necessary to determine the quantities of various items. With the help of drawings and specifications each item is taken with full description and length, width, depth is determined.
Items are expressed in m3, m2, and running metre and in numbers according to the mode of measurement while preparing estimates, in taking out quantities study of drawings, visit of site, sequences of operation accuracy, deductions of openings, etc. are followed.
Method of taking out quantities:
There are 2 methods of taking out quantities or methods of estimating:
1. P.W.D. method, 2. Centre line method.
(public works Department) (I) Load Bearing Structure:
59 1. Prepare foundation plan showing centre line with all dimensions. Centre to centre dimensions taken out by adding half width of each cross wall to inner dimensions of a room.
2. Now divide the walls in two groups. In plan, walls in horizontal direction are called long wall and vertical direction walls are short walls and vice versa.
*It is advisable not be change the grouping of wall to avoid errors.
3. Measure length of long wall for an item by using formula
Long wall length for an item = Length of centre line of long wall + Width of item 4. Measure length of short wall for an item by using formula.
Short wall length for an item = Length of centre line of short wall-Width of item This method is adopted by state P.W.D.
Advantages:
1. This method is simple and accurate.
2. There are no chances of mistake in calculation.
3. The method gives quantities quickly.
Centre Line Method:
1. Prepare the foundation plan of the given drawing. Write centre line lengths of each wall in it.
2. Find the total length of the centre lines of long and short walls, having same type of footing.
That corners of building where two walls meets are not taken in kuncions and if two walls meets a wall some point take n = 2 at that point.
4. For an item calculation of length is done as below:
Length for an item = Total centre line length –n (
width of item) N= number of junctions of cross walls with main walls
5. For buildings having different types of walls, each set of walls should be taken separately.
Advantages:
1. It can be used for calculation of quantities of rectangular, circular and polygonal buildings.
2. This method is simple and quick.
60 3. Calculation are easy and less.
Deductions of Openings: When area of volume of openings are to be deducted from various items like plastering pointing and brickwork for superstructure following rules should be used.
1. Measured the quantity without considering opening.
2. Deduct the openings quantity by considering bearings.
No deduction is made for the following in case of brickwork in superstructure:
1. Opening each upto 0.1 sq.m.
2. Ends of beams, posts, rafters, purlins upto 0.05sq.m. in secion.
3. Wall plates, bed plate, bearing of chaiia upto 10 cm depth.
4. Bearing of floors and roof slabs etc.
For opening of doors and windows and arches deductions from masonry is given below:
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Deduction = l
Rules for deductions in plastering and pointing:
1. No deduction is made for ends of beams, posts and rafters etc.
2. No deduction is made for small opening upto 0.5 sq.m. and no addition is made for jambs, soffits and sill of these openings.
3. For openings more than 0.5 sq.m. and less than 3 sq.m.
4. For opening above 3 sq.m. both faces are deducted and area of jambs, soffits and sill are added.
(II) For Farmed Structure Building:
[A] R.C.C. works.
R.C.C. works complete in one item, including concrete, steel a 2. Whole R.C.C. work is divided in three parts:
(a) Concrete works;
(b) Steel works;
(a) Concrete works;
(b) Steel works;
(c) Centering and shuttering or form calculated.
Deduction = l
Rules for deductions in plastering and pointing:
1. No deduction is made for ends of beams, posts and rafters etc.
2. No deduction is made for small opening upto 0.5 sq.m. and no addition is made for jambs, soffits and sill of these openings.
3. For openings more than 0.5 sq.m. and less than 3 sq.m. Deduction is made for one face only.
4. For opening above 3 sq.m. both faces are deducted and area of jambs, soffits and sill are
(II) For Farmed Structure Building:
R.C.C. works complete in one item, including concrete, steel and form-work.
2. Whole R.C.C. work is divided in three parts:
shuttering or form-work and quantities of each above item are separately
62 2. No deduction is made for small opening upto 0.5 sq.m. and no addition is made for jambs,
is made for one face only.
4. For opening above 3 sq.m. both faces are deducted and area of jambs, soffits and sill are
work and quantities of each above item are separately
63 [B] Calculation of quantity of concrete:
It is calculated by determining by volume of concrete member (slab, column, beam, etc.) and expressed in cubic meter.
Note: According to I.S. 1200 no deductions are made for steel while calculating quantity of concrete.
[c] Calculation of quantity of steel:
Approximately the quantity of steel for a R.C.C. member can be calculated as below; when detailed drawings and designs are not available.
(a) For lintel and slab:
Quantity of steel = 0.7 to 1% of quantity of concrete (m3)
But steel is not expressed in cubic meter, so quantity in quintals is calculated by considering the densely of mild steel.
As 1 cubic mt. of steel = 78.5 quintal = 7850 kg 1 tonne= 1000kg
1 quintal = 100 kg (b) For beams:
Quantity of steel = 1 to 2 % (c) For columns:
Quantity of steel = 1 to 5%
(d) For foundation and footing:
Quantity of steel = 0.5 to 0.8%
For R.C.C. work finishing no extra payment is made.
Minimum cover for steel should be provided as below:
For slab- side cover 4 cm to 5 cm; top and bottom cover 1.2 cm to 2 cms. For beams – 2.5 cm to 5 cm.
[D] Measurement of length of reinforcement Standard hook:
[E] Bar bending schedule:
For guidance of supervisors and laborers it is provided. It is list of the reinforcement bars give in tabular form as below:
Sr. No. Description Shape of bar
It is the list of reinforcement bars in tabular form giving the particulars of bars, shape of bending with sketches, length of each bar, total length and total weight for each R.C.C. work, a schedule of bar or bar bending schedule is prepared. From this requirement of different size and length of bars may be known and bent up during the time of construction. Hooks are not provi
of Tor steel.
For guidance of supervisors and laborers it is provided. It is list of the reinforcement bars give
Shape of Dia. Of bar
in mm No. of bars
Total length of abr in mtr.
It is the list of reinforcement bars in tabular form giving the particulars of bars, shape of bending f each bar, total length and total weight for each R.C.C. work, a schedule of bar or bar bending schedule is prepared. From this requirement of different size and length of bars may be known and bent up during the time of construction. Hooks are not provi
64 For guidance of supervisors and laborers it is provided. It is list of the reinforcement bars given
length of abr in mtr.
Wt. in kg
It is the list of reinforcement bars in tabular form giving the particulars of bars, shape of bending f each bar, total length and total weight for each R.C.C. work, a schedule of bar or bar bending schedule is prepared. From this requirement of different size and length of bars may be known and bent up during the time of construction. Hooks are not provided in case
65 Weight of different bars: This table should be referred while calculating quantity of steel.
Dia. In mm Wt. in kg/mtr. Dia. In mm Wt. in kg/mtr.
The following provisions are made in the estimate other than the items of work, their quantities and cost:
(1) Provision of contingencies:
During the execution of works there will be some miscellaneous expenditure which cannot be classified under any subhead or any item. These are the expenses of misc. character. To meet such expenses, 3 to 5% of estimated cost is provided, which is known as contingencies. If there is a saving in the amount of contingencies, it can be used for extra items after getting the sanction from competent authority.
Tools and plants (T. and P.) : For a big work or project 1 to 1.5% of estimated cost is provided in estimate for purchase of tools and machinery required for execution of works.
(2) Work charged Establishment:
It is the establishment whose expenditure is directly charged to the works. During the period of construction, the service of work-supervisors, store clerk, mistry, chowkidar etc. are required.
These ae Temporary employees and their salary is paid from the amount of work charged
When the quantities of a particular item are not certain, provisional quantities are worked out and provided separately in the estimates for such items. For this purpose quantities are calculated from measurement of the drawing with certain assumptions of the probable increase and are kept
66 in bill of quantities. These items are marked us ‘provisional’. The payment of provisional quantities is made on the completion of these items of work, after knowing the exact nature.
Example:
1. Nature of soil is uncertain, below the ground so depth of footing may vary.
2. Lengthening or shortening of concrete piles.
(4) Provisional Sum:
While preparing an estimate, the details of a specialized item or special work done by specialists, are not known, some amount is provided in the estimate or bill of quantities for such items. It is called provisional sum.
Example:
Installation of lift, air conditioners fitting, installation of refrigerating machine. During the execution of work. Quotations are called for this specialized item from firms or contractors. The contractor is not allowed to alter the amount of provisional sum and if he does will be treated as invalid.
(5) Electrification, sanitary and water supply works:
While preparing the estimate, a lump sum provision of 20% is made in the estimate.
For water supply and sanitary - 8% of the estimated cost.
For electrification - 8% of estimated cost For electric fans - 4% of estimated cost.
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