Any construction building design as per the below step. In this article, we design only slab and next article next steps calculation.

**Slab Design****Slab Beam Design****Lintel Beam Design****Column Design****Plinth Beam Design****Footing Design**

Most Important Point In This Article

### Some Important Point for Slab Design

### Type of Slab

A slab is a plate element having a depth (D), Very small as compared to its length and width slab is used as floor or roof in building, carry uniformly distributed load.

Slab may be

**Simply Supported****Continuos****Cantilever**

**Type of Slab Based on Support Conditions Are:**

1). One Way Spanning Slab

2). Two Way Spanning Slab

3). Flat Slab Resting Directly on Columns Without Beams

4). Grid Slabs or Waffle Slabs

5). Circular Slab and Other Shapes

### One Way Spanning Slab

If the slab is supported on two opposite sides. it is called a one-way spanning slab. In this type of slab, lads are transferred on two opposite supports as shown below figure.

**One Way Slab**

If the slab is supported on four sides, and if ly/lx ≥ 3 one way spaning slab.

For any slab, if ly = lx, the slab has a tendency to bend in both the directions Which increase is provided along lx (Short Span)

### Two Way Spanning Slab

It the slab is supported on all four edges and if ly / lx < 2,

The tendency of the slab is to bend in both directions. Such slabs are called a two-way slab. ( as shown below figure.)

In a two-way slab, the main reinforcement is provided along with lx as well as ly direction.

### Flat Slab

When the slab is directly supported on columns, without beams, it is known as a flat slab.

Flat slabs are provided to increased the floor height and to permitted a large amount of light which might be obstructed by the depth of beams.

### Grid Slabs

When the slab is required on beams with columns only on the periphery of the hall, the slab is called grid slab

Sometimes, in a large hall, public places, marriage halls, auditoriums, etc. a large column-free area is required. In these cases, large deep beams may be permitted but the columns are permitted only on the periphery

### One Way Simply Support Slab Calculation /Design

One Way Simply Support slab Below Point Calculation Required

**1. Effective Depth (d)**

**2. Effective Span**

**3. Reinforcement Requirements**

**4. Check for Cracking**

**5. Check for Deflection**

**6. Check for Development Length (Ld)**

### Effective Depth (d)

**For deflection control **

**L/d = 20 X M.F**

**M.F. Modifiction factor from— IS: 456, p.38.Fig-4****Assume % steel 0.3 to 0.6%**

**Fs = 0.58 Fy X (Ast requierd / Ast Provied)**

Initially assume that **Ast reqierd** = **Ast Provided **

Fy = 250 N/ Sq.mm —– Fs = 0.58 X 250 = 145 N/ sq.mm.

Fy = 415 N/ Sq.mm —– Fs = 0.58 X 415 = 240 N/ sq.mm.

Fy = 500 N/ Sq.mm —– Fs = 0.58 X 500 = 290 N/ sq.mm.

### Effective Span

Clear Span + d

c/c of Supports

Whichever is smaller ——– as per IS 456-2000 P. 34, CI 22.2.a

### Reinforcement Requirements

**Minimum reinforcement **

For Fe-250 Pt = 0.15 % of total C/s area (d x D)

For Fe-415 Pt = 0.12 % of total C/s area (d x D)

For Fe-500 Pt = 0.12 % of total C/s area (d x D) ——– as per IS 456-2000 P. 48, CI 26.5.2.1

**Maximum diameter (Sp 34)**

**For minbar:**

- Plain bars———–10 mm Ø min dia

Deformed bars—–8 mm Ø min dia

**For Distribution bars:**

- Plain bars———–6 mm Ø min dia

Deformed bars—–6 mm Ø min dia

**Check for Cracking**

**For Min Steel:**

3d ——— Where. d = Effective depth

300 mm

Spacing should not exceed smaller these two values.

**For Distribution steel:**

5 d

450 mm

Spacing should not exceed smaller these two values. ——- IS: 456-2000, P.46

**Check for Deflection**

Allowable **L/d = 20 X M.F.**

- M.F is Obtained from IS:456-200 P-38 Fig 4

Find actual, L/d

If Actual **L/d** < allowable **L/d** ———- Ok

### Check for Development Length (Ld)

IS 456-2000,P.44, Cl. 26.2.3.3 C

**Ld should be ≤ 1.3 (M1/V) + L0**

Where

**Ld = (Ø.σs / 4 τ bd )—————–σs = 0.87 fy** As per IS 456-200, P.42

50 % of steel is bent up near support. Therefore find M.R for 50 % of steel only

**M1 = M.R. for 50% steel support**

**V = Shear force at the support **

**L0 = Sum of anchorage beyond the center of support**

** d**

**12 Ø**

Take **L0** as the smaller of two values.

### One Way Simply Support SlabCalculation /Design- Example

Sum Point Consider As below

Slab Size 3.2m X 9.2 m

The slab is resting on 300mm thick wall

Find One Way Slab or Two Way Slab

ly/lx = 9.2 / 3.2 = 2.875 **> 2 **

As per the type of slab

**Here this one-way slab, **So we design the slab as one-way simply supported slab

**Effective Depth (d)**

Here Consider shorter span as l,

l = 3200 mm = 3.2 m

**l/d = 20 x M.F**

fy – 415 N/sq.mm, fs = 240 N / Sq.mm

M.F = 1.15 | As per IS Code 456, Fig.4

l/d = 20 x 1.15

3200/d = 20 x 1.115

d = 139.13 mm

Here, d = 150 mm , Assume 10 mm Ø bars

Overall Depth, D = 150 + (Ø / 2 ) + Clear Cover

**D = 175 mm**

**Effective Span**

1). 3200 + 150 = 3350 mm

2). c/c of Supports = 3200 + 300 = 3500 mm | IS: 456-2000,P-34, CI. 22.2.a

Whichever is smaller

Effective Span = l = 3350 mm = 3.35 m.

**Reinforcement Requirements**

**Load Calculations**

Dead load | 4.375 | Kn/m |

Floor Finsh | 1 | Kn/m |

Live Load | 2.5 | Kn/m |

Total Load |
7.875 |
Kn/m |

**Factored Load = 1.5 x 7.875**

**w = 11.82 kn/m.**

**Bending Moment**

Mu = (w. l^{2}) / 8 = (11.82 / 3.35^{2})

Mu = 16.58 Kn.m.

**Main Steel**

Pt = 50 (fck/fy) [1 – √ ( 1 -{(4.6 Mu)/ (fck x bd^{2})})]

Pt = 50 x (0.482) x (0.0945)

Pt = 0.215 %

Ast = ( pt / 100) x 1000 x 150

Ast = 322.5 mm^{2}

**For Spacing **

Sapcing = ({[π/4] x d^{2}}/Ast ) x 1000 mm

Sapcing = ( 78.53 / 322.5 ) x 1000 =** 243.50 mm**

**Distrbution Steel **

Provide a minimum of 0.120% of Total C/s Area | As per IS 456-200 P 48, CI. 26.5.2.1

Ast = (0.12/100) x 1000 x 175 = 210 Sq.mm

**Check for Cracking**

**For Main Steel**

1). 3 d = 3 x 150 = 450 mm

2). 300 mm | IS 456-2000 P-46

240 mm provided < 300 mm …………….. o.k.

**For Distribution Steel **

1). 5 d = 5 x 150 = 750 mm

2). 450 mm

130 mm provided < 450 mm …………….. o.k.

**Check for Deflection**

Allowable (l/d) = 20 x M.F.

% pt Provided = 100 Ast / bd = (100 x 327) / (1000 x 150) = 0.218% | IS Code 456-2000 P.38, Fig 4

M.F = 1.6

Allowable l/d = 20 x 1.6 = 3350 / 150 = 22.33

22.33 < 32 …………….. o.k.

**Check for Development Length (Ld)**

1). d = 150 mm

2). 12 Ø = 12 x 10 = 120 mm

Taking larger of two values L0 = 150 mm

S.F. at support = 50% of East at mid-span = 327 / 2 = 163.5 Sq.mm

M1 = 0.87 x 415 x 163.5 x 150 x [1-(415 x 163.5) / (20 x 1000 x 150)]

M1 = 8.65 x 10^{6} N.mm = 8.65 kN.m.

1.3 [ M1/V] + L0 = 1.3 x (8.65 x 10^{6} ) / (18.91 x 10^{3} ) + 150

M1 = 744.65 mm

for M 20 , fy = 415 N/mm^{2}

10 mm Ø. bar, tension

Ld = 470 mm

470 mm < 744.65 mm …………….. o.k.

**Reinforcment Details **

### One Way Simply Support Slab Calculation /Design Excel Sheet – Download

## Video tutorial for better understanding:

### Design of a Building

**Building design** refers to the broadly based architectural, engineering and technical applications to the **design** of **buildings**. All **building** projects require the services of a **building** designer, typically a licensed architect.

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**Suggested Read –**

- How to Structural Design a Building/House Step by Step Part-1 (One Way Simply Support Slab)
- How to Structural Design a Building/House Step by Step Part-2 (Two Way Simply Support Slab)
- How to Structural Design a Building/House Step by Step Part-3 (Slab Beam Design)
- How to Structural Design a Building/House Step by Step Part-4 (Column Design)

Md Nuruzzaman says

very good post. i am a civil engineer at bangladesh. need more post like that. if one end continius on end discontinuous .

Krunal Rajput says

Thanks, Dear

Emmanuel Kwabdins says

Hy I am Emmanuel Kwabdins from Nigeria, please can I have this as a PDF?

Krunal Rajput says

Thanks for comment

How to get easy pdf

Go to Print or ctrl + p button press,

Then select print PDF,

After select print then click ok to print for get your PDF file

Md Moynuddin says

You have added lots of information about Structural design of building, I appreciate the post

Krunal Rajput says

Thanks