235 APPLIED MECHANICS 
shown in Figs. 358 and 359. Two channels braced together make a 
favourite form of strut. ; 
If a strut is equally free to bend in two directions at right angles to 
one another, its component parts should be chosen and arranged so that 
++ RE RETR ei, © Leta 
ia 
I 
cast Tron Distance Piece. 
Fig. 357. Fig. 358. Fig. 359. 
the radii of gyration” of the section about axes perpendicular to these 
directions are as nearly as possible equal. 
The parts of a built up strut between the points of attachment of the 
secondary bracing should be examined as separate short columns hinged 
at their ends. ; 
Secondary bracing usually consists of light flat bars, 2 inches to 2$ 
inches in width, and + inch to 3 inch in thickness. Light angles about 
