assume rolled I section

assume $\lambda$=100 $fcd=\frac{kL}{xyy}=118$

zz axis class a yy axis class b

service load =700kN

factored load=$1.5\times$700=1050kN

length=7m-----z axis

length=5m--- z axis

Ae=2

P=Ae$\ast fcd$

1050$\ast 10^{3}=Ae\ast118$

Ae=8898.30mm$^{2}$

select ISHB 350 haviing area 9221 mm$^{2}$

ISHB 350 A=9221mm$^{2}$ bf=250 ff=11.6 fw=10.6

rxx=146.5mm

ryy=52.2mm

$\lambda x=\frac{kL}{rzz}=\frac{7000}{146.5}=47.78\lt 180$ $\ …