COLUMNS Columns are vertical compression members in structures, the effective length of which exceeds three times its lateral dimension. Which are provided for bear the load of Beam, Slab, etc. since columns support beams and slabs, so the failure of column results in the collapse of structure. Classification of columns: A. Classification on the basis of its shape: I. Square column, II. Rectangle column, III. Circular column, IV. Desired polygon. B. Classification on the basis of its slenderness ratio: I. Short column & II. Long column. C. Classification on the basis of the manner of loading: I. Axially loaded column, II. Column subjected to axially load and uni-axial bending, III. Column subjected to axially load and bi-axial bending. D. Classification on the basis of the type of lateral reinforcement provided: I. Tied columns in which separate or individual ties are provided surrounding the longitudinal reinforcement. II. Spirally reinforced columns in which helical bars are provided surrounding the longitudinal reinforcement.
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COLUMNS
Columns are vertical compression members in structures, the effective length of which
exceeds three times its lateral dimension. Which are provided for bear the load of Beam, Slab, etc.
since columns support beams and slabs, so the failure of column results in the collapse of structure.
Classification of columns:
A. Classification on the basis of its shape:
I. Square column,
II. Rectangle column,
III. Circular column,
IV. Desired polygon.
B. Classification on the basis of its slenderness ratio:
I. Short column &
II. Long column.
C. Classification on the basis of the manner of loading:
I. Axially loaded column,
II. Column subjected to axially load and uni-axial bending,
III. Column subjected to axially load and bi-axial bending.
D. Classification on the basis of the type of lateral reinforcement provided:
I. Tied columns in which separate or individual ties are provided surrounding the longitudinal
reinforcement.
II. Spirally reinforced columns in which helical bars are provided surrounding the longitudinal
Diameter of Transverse reinforcements will be maxm of,
A) 5 mm,
B)
Diameter of longitudinal bar.
so provide 5 mm dia bar as tie.
Spacing of Transverse tie centre to centre is minm of,
a) The least lateral dimension of the column,
b) 16 diameter of longitudinal bar,
c) 48 diameters of transverse ties,
Hence provide 5 mm ties @ 240mm c/c.
Example 2: A short column of square section is to be designed to carry an axial load of 1023 KN. Design the column as per I.S. code. Permissible stress in concrete and steel are 5 N/mm2 and 130 N/mm2 . Soln : given data, 2
2
From I.S. code longitudinal reinforcement in column must lie between 0.8 % to 6.0 % of C/S area. Let us provide 2.0% steel area of total C/S area.
Example 2: A rectangular column section 450mm x 600mm is acted upon by an axial load of 500 KN. Mx and My = 25KNm each. The steel provided is 8-20mmØ bars with an effective cover of 40 mm. check the safety of the section. [BNMU 2009]
Soln:
Axial load, P = 500 KN= 500 x 103 N
Mx = P x ey & My = P x ex
.’. ex & ey both are equal,
So,
Mamm eccentricity to avoid tensile stress;
It is clear that no tension develops anywhere in the column. So we can analyse the column as an uncracked section.