RHS 160×80×4.5 - Section Properties

RHS 160×80×4.5 has a mass of 16.24 kg/m, tabulated to EN 10219. A 12 m length therefore weighs about 195 kg, which is the figure to use for a steel take-off or when checking a lift.

RHS 160×80×4.5 has a depth of 160 mm, a width of 80 mm, a wall thickness of 4.5 mm, with a cross-sectional area of 20.6 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 106 cm³, and the elastic modulus Wel,y is 84.9 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 38 kNm before any stability check.

The second moment of area about the major axis, Iy, is 679 cm⁴, and about the minor axis Iz is 229 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 5.75 cm about the major axis and iz is 3.33 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 3.33 cm a 0.3 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 547 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.