Given

ISMB 350 bf==140mm tw=8.1mm

ISHB 300 bf=250mm tf=10.6mm

fub=400mpa

fy=250mpa

fu=410mpa

Required stiffness seat angle connection

Step I

length of seat angle bf=140mm

bearing length of seat angle (b)=$\frac{R}{tw\times \frac{fy}{ymo}}$

=$\frac{320}{8.1\times\frac{250}{1.1}}$

b=173.8mm

provide clearance 10mm

Required length of outstandard leg

=173.83+10 =183$\approx$ 200mm

provide seat angle size 200$\times$150$\times$10

Step …