Here we will learn with some simple examples how to calculate Effective Span of Beam & Slab of various type As per IS 456 2000 Clause 22.2.

**Effective span**: It is that length of **Beam** or **Slab**
using which we can calculate the moment acting on it & it is further
help us to ** design** &

**the members. (Show in**

*analyze***Fig:1**) [

*IS 456 2000 Clause 22.2*]

**Clear span**: It is the clear distance between
two supports over which the member (**Beam** or **Slab**) resting. (Shown in **Fig
:1**)

**Fig:1 Simply supported Beam & Slab**

**Effective depth**: It is the distance between top most
compression fiber of the concrete member (Beam or Slab) to the center of the
tension reinforcement. (Shown in **Fig:3**) [All Beam & Slab here have same dimension profile shown below]

Effective span is an
important parameter for design & analysis of a structure parts like **Beams**
& **Slabs** also its necessary for calculating **“MOR” **(**Moment
of resistance***:*the moment which can be safely withstand by a structure
or parts of structure’s without showing any considerable deformation), but the effective span depends on lots of other factors, because of that we divided effective span into **Four main categories:-**

**a) Simply supported Beam & Slab**

**b) Continuous Beam & Slab**

**c) Cantilever Beam & Slab**

**d) Frames**

*a) ***Simply supported Beam & Slab:**** **The effective span of a member that is **not built
integrally (monolithic-ally) with its supports **shall be taken as lesser than
of these two: -

Clause (i): **Clear Span
(L) + effective depth (d)** (shown in fig:2 &2.1)

**Or**

Clause (ii): **Clear Span (L) + support/2 +support/2 (****Center**** to ****Center**** distance b/w support)**

**Fig:3 Simply supported beam with 200 mm wide support**

** Example 1**: (as shown in fig 1; where
span length= 3000 mm & width of support= 300 mm)

* Clause i)*

Effective span of the Beam = Clear Span (L) + effective depth (d)

= 3000 mm + 252 mm

= *3252 mm*

* Cause
ii)*

Effective span of the Beam = Clear Span (L) + support/2 +support/2 (Center to Center distance b/w support)

=3000 mm+300 mm/2+300 mm/2

=3300 mm

**“here the
Clause(i) is the deciding clause of the effective length (L)= 3252 mm <
3300 mm (Clause ii)”**

** **

** Example 2**: (as shown in fig 2; where
span length= 3000 mm & width of support= 200 mm)

* Clause
i)*

Effective span of the Beam = Clear Span (L) + effective depth (d)

= 3000 mm + 252 mm

= *3252
mm*

* Cause
ii)*

Effective span of the Beam = Clear Span (L) + support/2 +support/2 (Center to Center distance b/w support)

=3000 mm+300 mm/2+200 mm/2

= 3200 mm

*“here the
Clause(ii) is the deciding clause of the effective length (L)= 3200 mm <
3252 mm (Clause i)”*

*b)*

**If the member (Beam or Slab) continuous over more than two support then it’s called continuous Slab or Beam.**

*Continuous Beam or Slab:*if the width of the support is less
than 1/12 of the clear span, the effective span of a continuous Beam or Slab is
calculated as per clause (**a**) explain above. (As shown in Fig:4)

*width of support < 1/12 of clear span*

*or*

*12 x width of support** < clear span (we can write this
expression mathematically)*

“**The clear span length should be greater than twelve times of width**”

If the supports are wider than 1/12
of the clear span or 600 mm whichever is less, the effective span shall be
taken by following below mentioned criteria’s

**Width of support > 1/12 of clear
span**

Or

**12 x width of support > clear span** *(we can write this expression
mathematically)*

“**The clear span should be less than twelve times of support width**”

**1)** **For end span**
with **one end fixed** and the **other continuous** or for intermediate
spans. the effective span shall be the clear span between supports.

*Effective
span = Clear span*

**Fig 4: Continuous Beam with one end of the span ‘fixed’**

**Example**: As shown in fig 4;

For Span 2: effective spa = clear span = 3400 mm (This is the intermediate span)

[All span is less than twelve times of the width which is 3600 mm]

**2) ****For end span**
with **one end free** & **other continuous** the effective span shall
be equal to lesser of these TWO

Or

Clause (ii) Clear span + width of support/2

**Fig 5: Continuous Beam or Slab with one end of the span ‘free’**

**Example 1**: (as shown in **fig 5**; where
span 1; clear span= 3500 mm; support width= 300 mm; effective depth=252 mm)

Clause (i) Clear
span + effective depth (d)/2 = 3500 + 252/2 = 3626
mm

or

Clause (ii) Clear
span + width of support /2 = 3500 + 300/2 = 3650 mm

* Here clause (i) is the deciding
clause for the effective length =3626 mm*

**Example 2**(as shown in **fig 5**; where span
3; clear span= 3850 mm; support width= 200 mm; effective depth=252 mm)

Clause (i) Clear
span + effective depth (d)/2 = 2300 + 252/2 = 2426 mm

or

Clause (ii) Clear span + width of support /2 = 2300 + 200/2 = 2400 mm

** Here clause (ii) is the deciding
clause for the effective length = 2400 mm**

[All span is less than twelve times of the width which is 3600 mm & 2400 mm]

** 3)** **For Roller or Rocket bearing**

**Effective
span = Center to center distance between support**

= clear span +
roller dia/2 + roller dia/2

= clear span
+roller radius +roller radius

= clear span + dia of roller

**Fig: 6 Continuous roller supported Beam or Slab**

**Example:** as show in **fig 6**; clear span
=3400 mm; roller dia=250 mm

Effective span = clear span + dia of
roller

= 3400 + 250

= 3650 mm

[All span is less
than twelve times of the width which is 3600 mm]

**c)** **Cantilever Beam & Slab: **The cantilever beam or slab are categorized
into two types for calculating their effective length there are:

**Fixed at the end (not continuous over support):**For these cantilever bear or slab effective length consider as the clear length from the face of the support plus effective depth. (as shown in**fig:7**)

**Effective length = length from face
of the support + effective depth(d)**

**Fig:7 Cantilever Beam or Slab fixed at end**

**Example:** as show in **fig 7**; clear length
=1350 mm; effective depth (d) = 252 mm

Effective length= 1350 mm + 252 mm

= 1602 mm

**Continuous over support**: The cantilever which is continuous over support to form a cantilever, the effective length of that cantilever should be taken as length from face of the support plus half the width of the support.

**Effective length = length from face
of the support + support width/2**

**Fig:8 Cantilever Beam or Slab continuous over support**

**Example:** as show in **fig 8**; clear
length =1410 mm; support width = 300 mm;

Effective length= 1410 mm + 300/2

= 1410 mm + 150 mm

= 1560 mm

**d)** **Frame: **For analysis of continuous frame **center to center** distance shall be
consider for effective length.

**Effective
length= C****enter to center**

** = Clear span + width of support/2**

**Fig:9 Frame structure of Beam & Slab**

**Example:** as show in **fig 9**;** Frame 1**;
clear span =3600 mm; support width = 300 mm;

Effective length= 3600 mm + 300/2

= 3750 mm

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