8.0 COLUMNS AND STRUTS
8.1 Introduction
A column or strut is a structural member subjected to axial compressive loads. If the member is vertical
with both of its ends fixed rigidly, it is known as a column. If the member is not vertical and one or both
of its ends are hinged or pin-jointed, the bar is known as a strut. We can find examples of struts in
compression members of a truss. Examples of columns and struts are as shown in Figure 10.1 below:
Figure 10.1: (a) Columns in an RC building (b) A strut in a truss
8.2 Failure of a column
Failure of a column occurs due to any one of the following stresses set up in the column:
(i) Direct compressive stresses;
(ii) Buckling stresses;
(iii) Combination of direct compressive and buckling stresses.
10.2.1 Failure of a short column
A short column is one whose ration of effective length to its least lateral dimension is less than or equal
to 12. Consider a short column of uniform cross-sectional area 𝐴 subjected to an axial compressive load
𝑃, in Figure 10.2 below:
Figure 10.2
, The compressive stress induced is given by:
𝑃
𝜎=
𝐴
If the compressive load on the short column is gradually increased, a stage will reach when the column
will be on the point of failure by crushing. The stress induced in the column corresponding to this load is
known as crushing stress and the load is known as crushing load. All short columns fail by crushing.
𝐿𝑒𝑡 𝑃𝑐 = 𝑐𝑟𝑢𝑠ℎ𝑖𝑛𝑔 𝑙𝑜𝑎𝑑
𝜎𝑐 = 𝑐𝑟𝑢𝑠ℎ𝑖𝑛𝑔 𝑠𝑡𝑟𝑒𝑠𝑠
𝐴 = 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
𝑃𝑐
𝑇ℎ𝑒𝑛, 𝜎𝑐 =
𝐴
Figure 10.3 shows a column that has failed by crushing.
Figure 10.3
10.2.2 Failure of a long column
A long column is one whose ratio of its effective length to its least lateral dimension is greater than 12.
Consider a long column of uniform cross-sectional area 𝐴 and length 𝑙 as shown in Figure 10.4 (a):
8.1 Introduction
A column or strut is a structural member subjected to axial compressive loads. If the member is vertical
with both of its ends fixed rigidly, it is known as a column. If the member is not vertical and one or both
of its ends are hinged or pin-jointed, the bar is known as a strut. We can find examples of struts in
compression members of a truss. Examples of columns and struts are as shown in Figure 10.1 below:
Figure 10.1: (a) Columns in an RC building (b) A strut in a truss
8.2 Failure of a column
Failure of a column occurs due to any one of the following stresses set up in the column:
(i) Direct compressive stresses;
(ii) Buckling stresses;
(iii) Combination of direct compressive and buckling stresses.
10.2.1 Failure of a short column
A short column is one whose ration of effective length to its least lateral dimension is less than or equal
to 12. Consider a short column of uniform cross-sectional area 𝐴 subjected to an axial compressive load
𝑃, in Figure 10.2 below:
Figure 10.2
, The compressive stress induced is given by:
𝑃
𝜎=
𝐴
If the compressive load on the short column is gradually increased, a stage will reach when the column
will be on the point of failure by crushing. The stress induced in the column corresponding to this load is
known as crushing stress and the load is known as crushing load. All short columns fail by crushing.
𝐿𝑒𝑡 𝑃𝑐 = 𝑐𝑟𝑢𝑠ℎ𝑖𝑛𝑔 𝑙𝑜𝑎𝑑
𝜎𝑐 = 𝑐𝑟𝑢𝑠ℎ𝑖𝑛𝑔 𝑠𝑡𝑟𝑒𝑠𝑠
𝐴 = 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
𝑃𝑐
𝑇ℎ𝑒𝑛, 𝜎𝑐 =
𝐴
Figure 10.3 shows a column that has failed by crushing.
Figure 10.3
10.2.2 Failure of a long column
A long column is one whose ratio of its effective length to its least lateral dimension is greater than 12.
Consider a long column of uniform cross-sectional area 𝐴 and length 𝑙 as shown in Figure 10.4 (a):
