Slab and it's types
Slab
A concrete slab is a common structural element of modern building consisting of a flat, horizontally surface made of cost concrete. Steel reinforced slab normally between 100 mm to 500 mm thick are most often slab is use to construct floors and ceilings and some other ways.
It is generally supported from the beam, columns,walls and the ground. The modern slabs are usually made up of concrete and the technical word which is use for this kind of slab is RCC slab it mean reinforced cement concrete slab. It is a crucial structural element and used to provide flat surfaces in floor and ceilings of buildings. The slab which is use in between the foundation of building or structure between the ground is known as floating slab or grade slab.
Types of Slab
There are two types of slab
- One way Slab
- Two way Slab
- One way Slab
- Two way Slab
One Way Slab:
One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. The ratio of longer span (l) to shorter span (b) is equal or greater than 2, considered as One way slab because this slab will bend in one direction i.e in the direction along its shorter span
Longer span ≥ 2
Shorter span
Due to the huge difference in lengths, the load is not transferred to the shorter beams. Main reinforcement is provided in shorter span and distribution reinforcement in a longer span..
Longer span ≥ 2
Shorter span
Two Way Slab:
Two way slab is a slab supported by beams on all the four sides and the loads are carried by the supports along with both directions, it is known as two way slab. In two way slab, the ratio of longer span (l) to shorter span (b) is less than 2.
Longer span < 2
Shorter span
In two way slabs, the load will be carried in both the directions. So, the main reinforcement is provided in both directions for two way slabs.
Longer span < 2
Shorter span
Quantity of Cement ,Sand and Aggregate Quantities in Slab
For the quantities of Cement , Sand and Aggregates in slab we have know the some other things so we can find these quantities quite easily .
Data
1- Length of Slab
2- Width of Slab
3- Depth of Slab
4- Ratio of Concrete
5- Dry Density which is constant
6- Number of CFT in one bag of Cement it is also constant
Procedure
After collecting data find the volume of slab then find it's dry volume . By adding the ratios of concrete we find the sum of ratio. At the end of this procedure divide the ratios of cement, sand and aggregate with sum of ratio then multiply it with dry volume of slab.
These are the basic information which is very essential to find the quantities of cement , sand and aggregates .
Data
( Ratio of concrete is 1 : 2 : 4 )
length of slab = L = 10'
width of slab = W =10'
depth of slab = D = .5'
dry density = 1.54 cft
Solution
volume of slab = L x W x D
v = 10 x 10 x .5 = 50 cft .
Dry Volume
Now we convert wet volume in to dry volume
Vd = wet volume x dry density
= 50 x 1.54
Vd = 77 cft .
sum of ratio = 1+2+4
= 7
Volume of cement
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v = 1 x 77
7
= 11 cft .
convert it in to bags of cement
Volume of 1 bag of cement = 1.25 cft
Numbers of bag in cft = v. of cement
= v. of bag
= 11 = 8.8 bags .
1.25
Volume of sand
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v = 2 x 77
7
= 22 cft .
Volume of Aggregates
v = 4 x 77
7
= 44 cft .
How can we find the quantity of steel and it's weight in Slab
Main Bars
Bars of steel which are use in shorter span known as main bars
Distribution Bars
Bars of steel which are use in longer span known as distribution bars
Information
Diameters of steel in meter
1" = 25 mm
4" = 100 mm
6" = 150 mm
8" = 200 mm
How can we find the quantity of steel and it's weight in Slab
Information
Diameters of steel in meter
1" = 25 mm
4" = 100 mm
6" = 150 mm
8" = 200 mm
Quantity or length of steel
Calculation of steel is very essential and it is the most important factor of construction. For the calculation of steel we have to collect some data which is given below.
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- Dimensions such as length and width of slab
- Diameter of bar
- Center to center distance
First of all we find the numbers of main and distribution bars the we multiply it with it's length or width so we find the total length of steel. After we find the unit weight of steel and multiply it with the total length.
Example 1
Example 1
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Data
Dimension of slab
Length of slab = 15 m
width of slab = 8 m
Diameter of bar = 10 mm
Center to center distance = 150 mm = 0.15 m
Number of main bars = 15 + 1
0.15
= 101 Nos
Number of distribution bars = 8 + 1
0.15
= 55 Nos
Length of main bars = 101 x 8 = 808 m
Length of distribution bars = 55 x 15 = 825 m
Total length of steel bars = 808 + 825 = 1633 m
Weight of steel
Unit weight of steel = D²
= 162.162
= ( 10 )²
=162.162
=.61 kg/m
Total weight of steel = Total length of steel x Unit weight of steel
= 1633 x 0.61 = 997 kg
Weight of solid steel bar in kg/m
Data
Diameter of steel bar = d = 10 mm = 0.01 m
Length of steel bar = 3 m
Density of steel = 7850 kg/m³
Solution
Volume of steel = π x d² x l
4
v = 3.14 x (0.01)² x 3
= 0.785 x 0.0001 x 3
= 0.000235 m³
Weight of steel bar = volume x density
= 0.000235 x 7850'
= 1.8447 kg/m
Weight of solid steel bar in kg/m
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Data
Diameter of steel bar = d = 10 mm = 0.01 m
Length of steel bar = 3 m
Density of steel = 7850 kg/m³
Solution
Volume of steel = π x d² x l
4
v = 3.14 x (0.01)² x 3
= 0.785 x 0.0001 x 3
= 0.000235 m³
Weight of steel bar = volume x density
= 0.000235 x 7850'
= 1.8447 kg/m
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