Design of Column

By Deepanshu Rastogi|Updated : December 2nd, 2021

Through Champion Study Plan for GATE Civil Engineering (CE) 2022, we are providing Design of Column 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 "Design of Column"  topic of the "Design of Concrete Structures" subject. 

 

Design of Column

 

Working Stress Method(Not in the GATE Syllabus)

Slenderness ratio (λ)

image039

If λ > 12 then the column is long.

Load carrying capacity for short column

image040

where, AC = Area of concrete, image041

σSC Stress in compression steel

σCC Stress in concrete

Ag Total gross cross-sectional area

ASC Area of compression steel

Load carrying capacity for long column

image046

where,

Cr = Reduction factor

image047

where, leff = Effective length of column

B = Least lateral dimension

imin = Least radius of gyration and image048

where, l = Moment of inertia and A = Cross-sectional area

Effective length of column

Effective length of Compression Members

image049

image050

image051

Column with helical reinforcement

Strength of the column is increased by 5%

image052 for short column

image053 for long column

Longitudinal reinforcement

(a) Minimum area of steel = 0.8% of the gross area of column

(b) Maximum area of steel

(i) When bars are not lapped Amax = 6% of the gross area of column

(ii) When bars are lapped Amax = 4% of the gross area of column

Minimum number of bars for reinforcement

For rectangular column  4

For circular column  6

Minimum diameter of bar = 12 mm

Maximum distance between longitudinal bar = 300 mm

Pedestal: It is a short length whose effective length is not more than 3 times of lest lateral dimension.

Transverse reinforcement (Ties)

image054

where image055 dia of main logitudnal bar

φ = dia of bar for transverse reinforcement

Pitch (p)

image057

where, φmin = minimum dia of main longitudinal bar

Helical reinforcement

(i) Diameters of helical reinforcement is selected such that

image058

(ii) Pitch of helical reinforcement: (p)

image059

where,

dC = Core diameter = dg – 2 × clear cover to helical reinforcement

AG = Gross area image060

dg = Gross diameter

Vh = Volume of helical reinforcement in unit length of column

φh = Diameter of steel bar forming the helix

image062

image063

dh = centre to centre dia of helix

= dg – 2 clear cover - φh

φh = diameter of the steel bar forming the helix

image064

Some others IS recommendations

(a) Slenderness limit

(i) Unsupported length between end restrains image065 60 times least lateral dimension.

(ii) If in any given plane one end of column is unrestrained than its unsupported length image066

(b) All column should be designed for a minimum eccentricity of

image067

Limit state method

  1. Slenderness ratio (λ)
    if image068
    λ<12 Short column
  1. Eccentricity
    image070
    If image071 then it is a short axially loaded column.
    where, Pu = axial load on the column
  2. Short axially loaded column with helical reinforcement
    image072
  3. Some others IS code Recommendations
    image073

(a) Slenderness limit

(i) Unsupported length between end restrains image065 60 times least lateral dimension.

(ii) If in any given plane one end of column is unrestrained than its unsupported length image065 image074

(b) All column should be designed for a minimum eccentricity of

image075

Concentrically Loaded Columns

Where e = 0, i.e., the column is truly axially loaded.

image076

This formula is also used for member subjected to combined axial load and bi- axial bending and also used when e > 0.05 D.

*****

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Thanks

All the Best

Comments

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Yash M

Yash MOct 10, 2017

Thank you sir.. Really helpfull information
Sruthi Surendran
What is the value for sigma sc and sigma cc for the load capacity of column in wsm??
Suresh Kumar
For effective length which value we learn..... Theoretical or recommend 😐😐😐
Uddipan Medhi
Very helpful.thanks
Wani Khalid

Wani KhalidJul 25, 2019

Solve some problems on RCC columns
Pramod Nani
Can I get it in PDF format
Elanaria Bluedevil
can u plz upload plate girder ar gantry girder notes plzz.plzzz
Suhaib Rasul

Suhaib RasulSep 28, 2020

footing part is not present where can i get it?

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