UPN 80 - Section Properties

UPN 80 has a mass of 8.6 kg/m, tabulated to Continental Steel. A 12 m length therefore weighs about 103 kg, which is the figure to use for a steel take-off or when checking a lift.

UPN 80 has a depth of 80 mm, a width of 45 mm, a web thickness of 6 mm, a flange thickness of 8 mm, with a cross-sectional area of 11 cm². These are the nominal dimensions from Continental Steel; rolling tolerances apply to the delivered section.

The elastic section modulus about the major axis, Wel,y, is 26.5 cm³. Use it with M_el,Rd = Wel,y x f_y / gamma_M0 for an elastic check.

The second moment of area about the major axis, Iy, is 106 cm⁴, and about the minor axis Iz is 19.4 cm⁴. Iy is the value deflection depends on - for a simply supported beam under a uniform load, the midspan deflection is 5wL⁴/384EIy - so on spans where a deflection limit governs rather than strength, this is the number that decides the section.

iy is 3.1 cm about the major axis and iz is 1.33 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 1.33 cm a 0.1 m effective length already gives lambda = 100. Minor-axis buckling almost always controls unless the weak axis is restrained.