• A column is defined as a vertical compression
member which is mainly subjected to axial loads .
• Column transfer the load of
• superstructure to the foundation safely.
• Mainly column, struts and pedestals are used as
compression members in buildings, bridges.
• If the effective length exceeds three times its least
lateral dimension it is called column.
• If the Effective length is less than three times its
least lateral dimension is called pedestal.
5. 2.Material of Construction
a. Timber Columns:
• Timber columns are generally used for light loads. They are used in small
trusses and wooden houses. These are called as posts.
b. Masonry Columns:
• These are used for light loads.
c. R.C.C. Columns:
• R.С.С. columns are used for mostly all types of buildings and other R.С.С.
structures like tanks, bridges etc.
d. Steel Columns:
• Steel columns are used for heavy loads.
e. Composite Columns:
• Composite columns are used for very heavy loads. They consist of steel
sections like joists (I or H sections) embedded in R.C.C.
7. 3. Type of Loading
a. Axially loaded column:
• The columns which are subjected to loads acting along the
longitudinal axis or centroid of the column section are called as
axially loaded columns.
• Axially loaded column is subjected to direct compressive stress only
and no bending stress develops anywhere in the column section.
b. Eccentrically loaded columns:
• Eccentrically loaded columns are those columns in which the loads
do not act on the longitudinal axis of the column.
• They are subjected to direct compressive stress and bending stress
• Eccentrically loaded columns may be subjected to uniaxial bending
or biaxial bending depending upon the line of action of load, with
respect to the two axis of the column section.
9. 4. Slenderness Ratio
• The slenderness ratio of a compression member is defined as the
ratio of effective length to the least lateral dimension.
• The columns are classified as following two types depending upon
the slenderness ratio:
a. Short columns. b. Long columns.
a. Short Columns:
• The column is considered as short when the slenderness ratio of
column i.e ratio of effective length to its least lateral dimension (l/b)
is less than or equal to 12.
• If the slenderness ratio of the column is greater than 12, it is called as
long or slender column.
10. 5.Type of Lateral Reinforcement
• An R.С.С. column has longitudinal and lateral reinforcement. They can
also be classified according to the manner in which the longitudinal steel is
laterally supported or tied.
a. Column with longitudinal steel and lateral ties.
b. Column with longitudinal steel and spiral ties.
11. Effective Length
• The vertical distance between the
points of inflection of the
compression member in the
buckled configuration in a plane
is termed as effective length le of
that compression member in that
• The effective length is different
from the unsupported length l of
the member, though it depends on
the unsupported length and the
type of end restraints.
• The relation between the effective
and unsupported lengths of any
compression member is
• Le = K x L
12. 1. Longitudinal Reinforcement in columns (as per IS 456:2000)
a) The cross-sectional area of longitudinal reinforcement shall be not
less than 0.8 percent nor more than 6 percent of the gross cross-
sectional area of the column.
Note: the use of 6 percent reinforcement may involve practical
difficulties in placing and compacting of concrete, hence lower
percentage is recommended.
Where bars from the columns below have to be lapped with those in
the column under consideration, the percentage of reinforcement
steel shall usually not exceed 4 percent.
b) In any column that has a larger cross-sectional area than that
required to support the load, the minimum percentage of steel shall
be based upon the area of concrete required to resist the direct
stress and not upon the actual area.
c) The minimum number of longitudinal bars provided in a
column shall be four in rectangular columns and six in circular
13. • d) The bars shall not be less than 12mm in diameter.
• e) A reinforced concrete column having helical reinforcement
shall have at least six bars of longitudinal reinforcement
within the helical reinforcement.
• f) In a helically reinforced columns, the longitudinal bars
shall be in contact with the helical reinforcement and
equidistant around its inner circumference.
• g) Spacing of longitudinal bars measured along the periphery
of the column shall not exceed 300mm.
• h) In case of pedestals in which the longitudinal reinforcement
is not taken into account in strength calculations, nominal
reinforcement not less than 0.15 percent of the cross-sectional
area shall be provided.
• Note: Pedestal is a compression member, the effective length
of the which does not exceed three times the least lateral
14. (2) Transverse Reinforcement in columns:
• (a) A reinforced compression member shall have transverse reinforcement
or helical reinforcement so disposed that every longitudinal bar nearest to
the compression face has effective lateral support against buckling subject
• The effective lateral support is given by transverse reinforcement either in
the form of circular rings capable of taking up circumferential tension or
by polygonal links (lateral ties) with internal angles not exceeding 135
• The ends of the transverse reinforcement shall be properly anchored.
15. Pitch and diameter of lateral ties (as per IS
Pitch – The pitch of transverse reinforcement shall be
not more than the least of the following distances:
• a. The least lateral dimension of the compression
• b. Sixteen time the smallest diameter of the
longitudinal reinforcement bar to be tied
• c. Forty-eight times the diameter of the transverse
Diameter – The diameter of the polygonal links or
lateral ties shall be not less than one-fourth of the
diameter of the largest –longitudinal bar, and in no case
less than 5mm.