Maximum Size of Concrete Slab, Beam and Column | Calculation Formula
In this Article today we will talk about the Maximum Size of Concrete Slab | Concrete Slab Thickness | Maximum Thickness of RCC Slab | Maximum Height of Concrete Column | Maximum Length of Concrete Beam | Standard Size of Beam | Column Dimensions | Concrete Column Sizing | Minimum Concrete Thickness
Maximum Span/Length of the Beam:
The maximum span & depth of a beam (cantilever / simply supported / continuous) are decided by deflection limits
These deflection limits are defined in terms of L/d ratio, where ‘L’ is the effective span & ‘d’ is the effective depth of the beam member.
According To Is Code On Clause 23.2.1 of IS: 456 (2000) pg. no. 37 The same provisions are stipulated for beam spans of up to 10 m.
Cantilever; Span/d <= 7
Simply supported; Span/d <= 20
Continuous; Span/d <=26
Greater than 10m
Simply supported < = 20×10/span
Continuous < = 26×10/span
Thus, depending on the length provided, the minimum allowable depth of the beam member can be calculated, and likewise the maximum allowable span can be calculated using the L/d ratio for a given depth of the beam member.
Effective Span: Usually the c/c span of the beam member is taken into account for further reference. See clause 22.2 of IS:456 (2000) pg. 34
Effective depth: d = D – (cover)- (dia of bottom bar/2)
D = effective depth
D = overall depth
Standard Size of Beam:
In a residential building it is 9 ʺ × 12 ʺ or 225 mm × 300 mm standard size according to (IS codes). The minimum RCC beam size should not be less than 9 ʺ × 9 ʺ or 225mm × 225mm with the addition of a 125mm rcc slab thickness. Maximum Height of Concrete Column
Maximum Thickness/Size of Concrete Slab:
Maximum Size of Concrete Slab:
tandards such as ACI 318 specify the minimum thickness of the slab based on the length of the slab. Column Dimensions
- Simply Supported Slab = L / 20
- One End Continuous Slab = L / 24
- Both End Continuous Slab = L / 28
- Cantiliver = L / 10
However, in other criteria, they do not directly specify the minimum slab thickness.
|MINIMUM THICKNESS OF THE SLAB AS PER IS 456:2000|
|Simply supports slabs spanning in one direction||L/30|
|Simply supports slabs spanning in Two directions (Two-way slab)||L/35|
|Continuous slabs spanning in one direction||L/35|
|Continuous slabs spanning in Two direction||L/40|
Minimum Thickness of Concrete Slab:
Concrete is generally applied with a thickness of 2 inches or more, but the thicker it is, the stronger the slab will be. Four (150mm) inches is more common for a slab
Concrete Column Sizing or Column Dimensions
Maximum Allowable Height of a Column without any Brace or Tie:
So if the slenderness ratio of the rcc column is greater than 12, that the column is classified as a long column.
L (efff) has to be determined as per IS 456:2000
R (min) = ( I(min) /Area of cross-section )1/2
But simply it can be understood as if column size is of 250X 250 mm then as per slenderness ratio limit if 12
Slenderness ratio = Length /shorter dimension
i.e., 12= length/250
i.e., Length= 12 x 250=3000 mm
So if you make a column of size 250mm x 250mm it should not exceeds the height of 3m. if you need to build beyond it. It needs tie beams Minimum Concrete Thickness
Stanadard Size of Column:
The size of the columns depends on the total load on the columns. The minimum column size should not be less than 9 “x 9”. 9 ”x 9” columns are to be used for a single-story concrete grade M15 (1: 2: 4) structure (cement: sand: aggregate).
Maximum Column Size for Different Stories:
NO. OF STORY
|230mm x 230mm 9” x 9”|
|300mm x 300mm 12”x12”|
|750mm x 750mm 30” x 30”|
|800mm x 800mm 32” x 32”|
|600mm x 600mm 24” x 24”|
|450mm x450mm 18” x 18”|
|850mm x 850mm 34” x 34”|
|650mm x 650mm 26” x 26”|
|475mm x475mm 19” x 19”|
NOTE: These are the standard RCC column sizes, but it will increase or decrease with respect to the load.
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