Design the beam:

Design the beam of Example, if the compression flange is laterally unsupported, but the beams ends are fully restrained.

Solution

Try an ISWB-600 section @ 145.1 kg/m for which the following data is obtained.

D = 600 mm, t_f = 23.6 mm, t_w = 11.8 mm, d₁ = D - 2, t_f = 552.8 mm,

r_yy = 5.35 cm, I_xx = 115626.6 cm⁴

Effective length of compression flange

l_eff = 0.7 × span= 0.7 × 8000 = 5600 mm

We have T/t  = 23.6/11.8 = 2.0, d₁/t  = 552.8/11.8 = 46.8

∴ Using Table 1 (IS : 800) for f_y = 250, max permissible σ_bc = 107.2 MPa

Actual bending stress = M . y/I = (360 × 10⁶  × 300)/(115626.6 × 10⁴)

= 93.4 MPa < 107.2 MPa ∴ OK.