Thumb rules used in Building Construction.

Thumb rule: Thumb rule is a method of judging a situation or a calculation which is not exactly right but it is derived from the past experiences. Thumb rules for the different components of building are different. Some of them are described below.

Thumb Rule For Slab

1.   The minimum thickness of the concrete slab is 125mm or 5 inches.

2.   The minimum Dia of bar used in the slab is 8mm.

3.   The maximum Dia of the bar used in the slab is 1/8th times of the slab thickness.

4.   Steel required in the slab is 1% of the total volume of the concrete slab.

5.   Clear cover of 15 mm to 20mm should be provided in the slab.

6.   Fe 500 steel should be used in slab.

7.   Steel required for the residential building = 4.5 Kgs – 4.75 Kgs / sq. Ft.

8.   Steel required for the Commercial building  = 5.0 Kgs-5.50 Kgs/Sq. Ft.

9.   the volume of concrete required = 0.038 m3/sq.ft

10. M15 Grade of concrete or above it should be used in slab.

11. Spacing between reinforcement in slab should not be less then 150mm c/c.

 

Thumb Rule for Beam:

·        Steel required in beam is 2% of total volume of concrete.

·        Minimum clear cover of 40mm shall be provided in beams.

·        M20 grade of concrete should be used in beam construction.

·        Minimum 4 bars shall be provided in beams. 2 bars of 12mm at top and 2 bars of 10mm at bottom.

·        The Spacing between reinforcement in slab should not be less then 150mm c/c.

 

Thumb Rule for Columns:

• The Steel required in Column is 2.5% of total volume of concrete.

·         Minimum steel requirement in column is 0.8% of gross area of concrete
The Maximum steel requirement in column  is 6% of the gross area of concrete

• Spacing between Longitudinal reinforcement should not be more than 300mm.
• Minimum clear cover in column is 40mm. 25mm clear cover is provided if column is less than 200mm.
• Minimum dia of 12mm bars 4 numbers should be used in column.
• The maximum diameter of reinforcing bars in column should be not more than 50mm.
• Overlapping distance in longitudinal bars should not be less than 24 times the smallest bar dia.
• Maximum spacing of stirrups is 16D or B or 300mm whichever is less.
• Minimum size of column should not less then 9″ X 9″.
• For Ground +1floor  Structure 9″ X 12″ (225mm X 300mm) Column should be used.
• Maximum gap between two columns of size 9″ X 9″ should not be more than 4 meter.
• M20 Grade of concrete should be used in column.
• Fe 500 Steel is highly recommended for column reinforcement.
• The space between the Columns should be equally given in a grid so as to efficiently transfer the load.

 

Thumb Rule for Foundation

• Steel required in footing is 0.8% of total volume of concrete
• The clear cover of main reinforcement in footing is 50mm.
• A minimum 10mm bar shall be used for foundation footing.
• M20 grade of concrete or above should be used for foundation.
• Length, width and depth of foundation should not be less than 1 meter.
• Footing thickness should not be less than 40 cm.
• Pile foundation should be used if soil bearing capacity is less than 24 kN/m3.

 

Thumb rules of bricks

• Standard size of Bricks/blocks is 19cm X 9cm X 4cm.
• It’s Compressive strength is 36 KN/cm2
• Weight of first class brick ought to be 3.85 kg.
• Crushing or Pulverizing strength of brick is 10.5 MN/m2.
• Number of bricks in 1m3 of brick masonry is 550 bricks.
• Water absorption in bricks is 12% to 15%.

 

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