UPN 400 - Section Properties

UPN 400 has a mass of 71.8 kg/m, tabulated to Continental Steel. A 12 m length therefore weighs about 862 kg, which is the figure to use for a steel take-off or when checking a lift.

UPN 400 has a depth of 400 mm, a width of 110 mm, a web thickness of 14 mm, a flange thickness of 18 mm, with a cross-sectional area of 91.5 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 1,020 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 20,400 cm⁴, and about the minor axis Iz is 846 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 14.9 cm about the major axis and iz is 3.04 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 3.04 cm a 0.3 m effective length already gives lambda = 100. Minor-axis buckling almost always controls unless the weak axis is restrained.