Design of Truss Members:

Principal Rafter

A principal rafter AC or BC is designed for a maximum compression of 50,286 N.

The effectual length of one panel between joints

= 0.85 × L = 0.85 × 5.59/2 = 2.376 m

Select an IS angle 80 × 80 × 6 @ 7.3 kg/m

From the handbook: Area = 9.29 cm²

Radii of gyration, (r_xx) = r_yy = 2.46, r_uu = 3.11, r_vv = 1.56 cm

∴          Minimum, r_min = 1.56 cm

∴          Slenderness ratio, λ = 2376/15.6 = 152

corresponding to that the permissible stress in axial compression (for steel, f_y = 250) is σ_ac = 44 MPa.

This is increased by 33% to include wind effects

∴          σ_ac allowed = 1.33 × 44 = 58.5 MPa

∴          Allowed axial compression P = 58.5 × 929 = 54,365 N

> 50,286 N     ∴ OK.