Question

Two ISMCs 300 form a built -up compression member placed back to back and is subjected to an axial compressive load . The optimum spacing required between the two ISMCs for maximum load carrying capacity is _______mm.
ISM300 section specifications are area $=4546m{m}^2$
$r_{xx}=118.1mm,r_{yy}=20.18mmand{C}_{yy}=23.6mm$

Answer 1

For most optimum utilization
$I_{xx,combination}=I_{yy,combination}$
$\Rightarrow r_{xx}^2=r_{yy}^2+{(\frac{s}{2}+c)}^2$
$\Rightarrow (118.1{)}^2=(20.18{)}^2+{(\frac{s}{2}+23.6)}^2$
$\Rightarrow s=185.52mm$