Simple column design
Steel columns or stanchions have a tendency to buckle or bend
under extreme loading. This can be attributed to:
(a) length
(b) cross sectional area
(c) method of end fixing, and
(d) the shape of section.
(b) and (d) are incorporated into a geometric property of section,
known as the radius of gyration (r). It can be calculated:-
r¼ffiffiffiffiffiffi
I
Aswhere: I = 2nd moment of area
A = cross sectional area
Note: r,I and A are all listed in steel design tables, eg. BS 4-1.
The length of a column will affect its slenderness ratio and
potential to buckle. This length is calculated as an effective length
relative to the method of fixing each end. Examples of position and
direction fixing are shown on the next page. eg. A Universal Column
203 mm ¾ 203 mm ¾ 46 kg/m, 10 m long, position and direction
fixed both ends. Determine the maximum axial loading.
Effective length (l) = 0.7 ¾ 10 m = 7 m
(r) from BS 4-1 = 51„1 mm
Slenderness ratio =rl=^7 ¾^10
3
51 : 1= 137
From tables in BS 449-2, the maximum allowable stress for grade
S275 steel with slenderness ratio of 137 is 48 N/mm^2
Cross sectional area of stanchion (UC) = 5880 mm^2 (BS 4-1)
The total axial load =
(^48) ¾ 5880
103
= 283 kN (approx. 28 tonnes)
Structural Steelwork---Column Design