USEFULL CIVIL ENGINEERING TIPS FOR SITE ENGINEERS:

#USEFULL CIVIL ENGINEERING TIPS FOR SITE ENGINEERS:

#TOSETLANDSURVBEYINSTITUTE,SALEM.

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Following are the basic civil engineering tips you should be remembered while working on a construction site.

1. GRADE OF CONCRETE:

M5 – 1 : 4 : 8

M10 – 1 : 3 : 6

M15 – 1 : 2 : 4

M20 – 1 : 1.5 : 3

M25 – 1 : 1 : 2

2. CLEAR COVER TO MAIN REINFORCEMENT:

Footings: 50 mm

Raft Foundation (Top) : 50 mm

Raft Foundation (Bottom): 75 mm

Raft Foundation (Side) : 75 mm

Beam: 25 mm

Strap Beam: 50 mm

Column :40 mm

Slab: 15 mm

flat Slab: 20 mm

Staircase: 15 mm

Retaining Wall: 20 – 25 mm

Water Retaining Structures: 2 0- 30 mm.

Maximum water absorption by bricks – 15%

Compressive strength of bricks – 3.5 N/mm2

Density Of Bricks- 1600-1920 Kg/m3

Minimum thickness of slab – 125 mm

Dimension tolerance for cubes – +2

Maximum free fall of concrete – 1.50 m

Lapping should not be used for the bars having larger dia than 36 mm.

Binding wire required for steel reinforcement – 8 kg per MT

3 samples should be taken for every 100 m2 in core cutting test.

Maximum chair spacing – 1 m.

Minimum dia should be used in dowels rod – 12 mm.

Hook for strriups (one side) – 9D

No. of strriups = (clear span/spanning) + 1

Length of main steel in cantilever anchorage – 69D.

Minimum no. of bars in square column – 4

Minimum no. of bars in circular column – 6

Minimum dia of main bars and distributors in the slab – 8 mm.

Maximum dia of main bars and distributors in the slab – 1/8 of slab thickness.

All reinforcement should be free from mill scales, loose rust, and coats of paints, oil or any other substances.

3. SETTING TIME:

Initial setting time should not be less than 30 minutes.

Final setting time should not be greater than 10 hours.

4. REQUIRED CURING DAYS:

Super sulfate cement – 7 days

Ordinary portland cement – 10 days

Cement with minerals and admixtures – 14 days.

5. SLUMP VALUE (IS-456):

Lightly reinforced concrete: 25 – 75 mm.

Heavily reinforced concrete: 75 – 100 mm.

Trench fill : 100 – 150 mm ( for in-situ & tremie).

6. CUBE SAMPLES:

1 – 5 m3 : 1 No.

6 – 15 m3 : 2 No..

16 – 30 m3 :3 No.

31 -50 m3 : 4 No.

Above 50 m3 : 4 + 1 no. of addition for each 50 m3.

CENTER LINE METHOD OF ESTIMATION

CENTER LINE METHOD OF ESTIMATION

CENTER LINE METHOD OF ESTIMATION:

There are three different methods of estimation.

1.    Center line method.

2.    Long and short wall method.

3.    Crossing method.

In this article, I will discuss center line method briefly for the estimation of materials.

WHAT IS CENTER LINE METHOD:

In this method of estimation, the total center line length of walls in a building is first calculated, then the center line length is multiplied with the breadth and depth of respective item to get the total quantity at a time.

The center line length for different sections of walls in a building shall be worked out separately. For verandah walls or partition walls joining the main walls, the center line length shall be reduced by half of the breadth of the layer of main wall that joins with the partition or verandah wall at the same level. The number of such joints is studied first to obtain the center line length.

By using this method estimation can be finished more quickly. This method is as accurate as other methods (except unsymmetrical wall). This method is suitably used for estimating circular, rectangular, hexagonal, octagonal etc shaped building.

Let us take an example:

FOR ONE ROOM BUILDING:Fig 1

First we need to calculate total center line length of the building.

Total center line length = 2 x 5.3 + 2 x 4.3 = 19.2 m.

1. Earthwork in excavation = Total center line length x breadth x depth

= 19.2 x 0.9 x (0.3+0.3+0.3)

= 19.2 x 0.9 x 0.9

= 15.52 cu.m

2. Concrete in foundation = 19.2 x 0.9 x 0.3 = 5.18 cu.m

3. a) Brickwork in foundation for 1st footing = 19.2 x 0.6 x 0.3 cu.m

b) Brickwork in foundation for 2nd footing = 19.2 x 0.5 x 0.3 = 2.88 cu.m

4. Brickwork in superstructure = 19.2 x 3.5 x 0.3 = 20.16 cu.m

FOR TWO ROOM BUILDING:Fig 2

Total center line length = 2 x (5.3+5.3) + 3 x 4.3 = 34.1 m.

1. Earthwork in excavation = Total center line length x breadth x depth

= 34.1 x 0.9 x (0.3+0.3+0.3)

= 34.1 x 0.9 x 0.9

= 27.62 cu.m

2. Concrete in foundation = 34.1 x 0.9 x 0.3 = 9.20 cu.m

3. a) Brickwork in foundation for 1st footing = 34.1 x 0.6 x 0.3 = 6.13 cu.m

b) Brickwork in foundation for 2nd footing = 34.1 x 0.5 x 0.3 = 5.11 cu.m

4. Brickwork in superstructure = 34.1 x 3.5 x 0.3 = 35.8 cu.m

Thus you can estimate quantity of different items such as

Quantity of D.P.C = Total Centre line length x Breadth of foundation x Thickness of D.P.C

Quantity of plinth beam = Total Centre line length x Breadth of the beam x Depth of beam.

Quantity of wall plaster for 2 sides = Total centre line length x Height of wall x Thickness of plaster.

Quantity of Paint for 2 sides of wall = Total centre line length x Height of wall  x 2  = Area of paint in sq.ft

Formation of thumb rules for cement, sand and aggregates

Formation of thumb rules for cement, sand and aggregates

The purpose of thumb rules is to prepare the rough cost of the building or plain quantities estimates. You can’t get a perfect quantity with the thumb rule rather a rough quantity that is almost identical or less to the accurate quantity.

Definition of thumb rule: Thumb rule is defined as creating a constant number with previous experience as well as work experience in the jobsite each day. As for instance, required covered area is multiplied with thumb rule to obtain rough quantities of the material.

You can get more clear ideas on thumb rule on the basis of the following example :-

Assume that 3 different houses are built up with a covered Area of 1050 square feet each. In every house various quantities of Cement bags, Sand and Aggregates are utilized for the construction work. Therefore, a thumb rule is formulated for cement, sand and aggregates quantity estimations as follow 

IN 1ST HOUSE CONSTRUCTION:
Cement= 600 Bags (as for illustration).
Sand = 2,000 cubic feet.
Aggregates = 1700 cubic feet.

IN 2ND HOUSE CONSTRUCTION:
Cement = 590 Bags (as for illustration).
Sand = 1900 cubic feet.
Aggregates = 1600 cubic feet.

IN 3RD HOUSE CONSTRUCTION:
Cement = 570 Bags (just for example).
Sand = 1800 cubic feet.
Aggregates = 1500 cubic feet.

How thumb rule is formed here:-
To form thumb rule for every construction material, the average usage of every particular material should be selected.

CEMEN:
Average Consumption = (600 + 590 +570)/3
= 586.66 bags.

Now it is required to determine the quantity of cement that is used in 1 square feet area.
Covered area = Material consumption.
1050 sft = 586.66 bags.
1sft = (586.66/1050) bags.
1sft = 0.55 bags

So 0.55 is fundamentally considered as our cement thumb rule. Now, if it is required to work out the quantities of cements for 5,000 square feet area (if the conditions are identical), 0.55 should be multiplied with the covered area to obtain the cement quantity.