The load carrying capacity of compression members is greatly influenced by its slenderness ratio, a larger value of which reduces the allowable compressive stress. As the effective length is mostly fixed in such members, it is only the radius of gyration, which can be manipulated by the designer.
- In most of the rolled steel sections the minor radius of gyration is much smaller than the major one, thus reducing the strength of the member.
- This can be overcome by arranging two or more sections such that the radii of gyration about the two principal axes are approximately the same. A number of such arrangements are shown in Figure.
For the four angles joined with plates (Figure(e)) if dx ≈ 0.75 dy , then Iy will be not less than Ix. For the arrangement in Figure (f), keep dx ≈ 0.8 dy 25 mm.
The main structural elements along with the connecting system must act as one element, without any joint failure, relative movement or distortion.
As regards the lateral connecting system, shown by dotted lines in Figure, is concerned, two common methods used in structural engineering practice are
(a) Lacing, and (b) Battened.
Depending upon the system adopted we have different design procedures for each one of them.