RHS 75×50×3 - Section Properties

RHS 75×50×3 has a mass of 5.59 kg/m, tabulated to EN 10219. A 12 m length therefore weighs about 67 kg, which is the figure to use for a steel take-off or when checking a lift.

RHS 75×50×3 has a depth of 75 mm, a width of 50 mm, a wall thickness of 3 mm, with a cross-sectional area of 6.91 cm². These are the nominal dimensions from EN 10219; rolling tolerances apply to the delivered section.

The plastic section modulus about the major axis, Wpl,y, is 17.1 cm³, and the elastic modulus Wel,y is 13.9 cm³. Wpl,y is what sets the moment capacity of a Class 1 or 2 section: M_pl,Rd = Wpl,y x f_y / gamma_M0, so at S355 with gamma_M0 = 1.0 this section reaches about 6 kNm before any stability check.

The second moment of area about the major axis, Iy, is 52.2 cm⁴, and about the minor axis Iz is 27.8 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 2.75 cm about the major axis and iz is 2 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 2 cm a 0.2 m effective length already gives lambda = 100. Minor-axis buckling almost always controls unless the weak axis is restrained.

The St Venant torsion constant It is 59.3 cm⁴. Closed sections carry torsion in a shear flow around the perimeter, which makes them far stiffer in torsion than an open section of the same weight and is usually why one is specified.