Limit State Method

By Deepanshu Rastogi|Updated : December 2nd, 2021

Through Champion Study Plan for GATE Civil Engineering (CE) 2022, we are providing Limit State Method study notes and other important materials on every topic of each subject.

These topic-wise study notes are useful for the preparation of various upcoming exams like GATE CivilIESBARCISROSSC-JEState Engineering Services examinations and other important upcoming competitive exams.

The article contains fundamental notes on the "Limit State Method"  topic of the "Design of Concrete Structures" subject. 

 

Limit State Method

IS 456 Standards for Beams and Slabs and Columns

Effective span

A. Simply supported beams and slabs (leff)

byjusexamprep

image002

Here, l0 = clear span

w = width of support

d = depth of beam or slab

B. For continuous beam

(i) If width of support < 1/12 of clear span

image002

(ii) If width of support > 1/12 of clear span

(a) When one end fixed other end continuous or both end continuous.

leff = l0

image005

(b) When one end continuous and other end simply supported

image006

 

 

C. Cantilever

(i) image007 image008

(ii) image009 image010

D. Frames

image011

leff = Centre to centre distance

Control of deflection

(i) This is one of the most important check for limit state of serviceability.

(a) The final deflection due to all loads including the effect of temperature, creep and shrinkage and measured from as cast level of the support of floors, roofs and other horizontal members should not normally exceed span/250

(b) The deflection including the effect of temperature, creeps and shrinkage occurring after erection of partition and application of finishes should not normally exceed span/350 or 20 mm which ever is less.

(ii) The vertical deflection limit may generally be satisfied if

(a) Basic span to effective depth ratio for span upto 10m is

Types of Beams: image014

For cantilever → 7

For simply supported → 20

For continuous → 26

(b) For span > 10 m effective depth image016

Where 'A' is span to effective depth ratio for span upto 10m.

(c) Depending upon the tension reinforcement the value 'A' can be modify by multiplying a factor called modification factor (MF1)

effective depth image017

where, 

image018

(d) Depending upon area of compression reinforcement, value (A) can be further modified using a modification factor (MF2)

effective depth = image019

(e) For flanged beam : A reduction factor is used

(f) Deflection check for two way slab:

image020

Slenderness limit

  1. For simply supported or continuous beams
    image021 where, l0 = Clear span
    b = Width of the section
    and, d = Effective depth
  2. For cantilever beam image022
    1. Minimum tension reinforcement image023
    2. Maximum tension reinforcement = 0.04 bD
    3. Maximum compression reinforcement = 0.04 bD
      where, D = overall depth of the section
    4. Where, D > 750 mm, side face reinforcement is provided and it is equal to 0.1% of gross cross-section area (b × D). It is provided equally on both face.
    5. Maximum spacing of side face reinforcement is 300 mm.
    6. Maximum size of reinforcement for slab/beam is 1/8 of total thickness of the member
    7. Nominal cover for different members
      Beams → 25 mm
      Slab → 20 to 30 mm
      Column → 40 mm
      Foundations → 50 mm
    8. Moment and shear coefficient for beams/slabs

image024

 

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Comments

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Amit Singh Rana
Is it available in Hindi language?
Ramkrishan Soni
Thanks a lot
Aham Khan Ark
Thanks sir pls rcc se related aur bhi notes available kraye
Aham Khan Ark
Design method beam and slab and column ke notes pls
TOP 10 LIST
Here, For one way slab, the ratio of Lx/Ly should be greater than or equal to 2.
And for two way slab the ratio is less than 2.
Nikhil Kumar

Nikhil KumarFeb 23, 2020

In design of 2way slab... What is 'r' and 'w'?
Thakur

ThakurJul 2, 2020

sir
slab ke L/D ratio me L kon sa span hai
longer yaa shorter
Arjun Hodshil
Hello sir .. i need mcq questions for structural design 2 and structural design 3 subject
Sirichandana

SirichandanaSep 14, 2020

Sherya mam can I get ur no  I'm unable to contact uh I'm new to thiz

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