One Way Slabs

PREPARED BY:
Asst. Prof. GAURANG PRAJAPATI
CIVIL DEPARTMENT
ONE WAY SLAB
Mahatma Gandhi Institute Of
Technical Education
& Research Centre, Navsari (396450)
ELEMENTARY STRUCTURAL DESIGN
6TH SEMESTER
CIVIL ENGINEERING

INTRODUCTION
 A slab is a plate element having depth (D), very small as compared to its length and
width.
 Slab is used as floor or roof in buildings, carry uniformly distributed load.
 Slab may be
• Simply supported
• Continues
• Cantilever
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ONE WAY SLABS

TYPES OF SLABS BASED ON SUPPORT CONDITIONS:
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ONE WAY SLABS
1. One way slab
2. Two way slab
3. Flat slab resting directly on columns without beams
4. Grid slabs or waffle slabs

1. ONE WAY SLAB
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ONE WAY SLABS
 If the slab is supported by the beams
on two opposite sides, it is called one
way slab.
 In this type of slab, loads are
transferred on two opposite supports.
 Condition:
𝒍 𝒚
𝒍 𝒙
≥ 2, → One way slab.

1. ONE WAY SLAB
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ONE WAY SLABS
 For any slab if 𝑙 𝑦 = 𝑙 𝑥, the slab has a tendency to bend in both the directions. With
increase of 𝑙 𝑦, the tendency of bending along 𝑙 𝑦 is reduced and that of 𝑙 𝑥 is
increased.
 When
𝒍 𝒚
𝒍 𝒙
≥ 2, the slab bends only in x (Short) direction. So, Main reinforcement is
provided along 𝑙 𝑥 (Short span).
 So, when
𝒍 𝒚
𝒍 𝒙
≥ 2, the slab is called one way slab.

1. ONE WAY SLAB
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ONE WAY SLABS

2. TWO WAY SLAB
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ONE WAY SLABS
 If the slab is supported on all four edges and if
𝒍 𝒚
𝒍 𝒙
< 2, → Two way slab.
 The tendency of slab is to bend in both directions. Such slabs are called Two way
slabs.
 In two way slabs, Main reinforcement is provided along 𝑙 𝑥 (Short span) as well as 𝑙 𝑦
(long span).

3. FLAT SLAB
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ONE WAY SLABS
 When slab is directly supported on columns, without beams, it is known as flat
slab.
 Flat slabs are provided to increase the floor height and too permit large amount of
light which might be obstructed by depth of beams.

4. GRID SLAB
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ONE WAY SLABS
 When slab is supported on beams with columns only on the periphery of the hall, it
is known as grid slab.
 Sometimes in large halls, public places, marriage halls, auditoriums, etc. a large
column free area is required.
 In this cases, large deep beams may be permitted but the columns are permitted
only on periphery.
 The grid slabs may have rectangular grid or diagrid.

DIFFERENCE BETWEEN ONE WAY SLAB & TWO WAY SLAB
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ONE WAY SLABS
No. One Way slabs Two way slabs
1
𝒍 𝒚
𝒍 𝒙
≥ 2
𝒍 𝒚
𝒍 𝒙
< 2
2
The bending of slabs takes place in
shorter direction only.
The bending of slabs takes place in
both the directions.
3
Main reinforcement is provided along
𝑙 𝑥 (Short span).
Main reinforcement is provided
along both the directions.
4 Depth required is more. Depth required is less.
5
As thickness is more and the amount
of steel is also more, it is less
economical.
As thickness is less and the amount
of steel is also less, it is economical.

DIFFERENCE BETWEEN BEAM AND SLAB:
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ONE WAY SLABS
 Slab is analyzed as 1 m wide beam.
 Normally, compression reinforcement is not provided in slab.
 Shear reinforcement is not provided in slabs due to lower shear stress.
 Temperature (Distribution) reinforcement is provided perpendicular to the main
reinforcement.
 The thickness of slab is very small as compared to beam.

MINIMUM REINFORCEMENT FOR SLABS:
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ONE WAY SLABS
b = 1000 mm (As slab is analyzed as 1 m wide beam)
D = Overall Depth of slab
Pt min = 0.12% for Fe 415 & Fe 500
= 0.15% for Fe 250
IS 456
Clause No.: 26.5.2.1
Page No.: 48
𝑨𝒔𝒕 𝒎𝒊𝒏 =
𝑷 𝒕 𝒎𝒊𝒏.
𝟏𝟎𝟎
× 𝒃𝑫
Where,

REINFORCEMENT OF ONE WAY SLABS:
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ONE WAY SLABS

One Way Slabs

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