CHS 177.8×4.5 - Section Properties

CHS 177.8×4.5 has a mass of 19.23 kg/m, tabulated to EN 10219. A 12 m length therefore weighs about 231 kg, which is the figure to use for a steel take-off or when checking a lift.

CHS 177.8×4.5 has a depth of 177.8 mm, a width of 177.8 mm, a wall thickness of 4.5 mm, with a cross-sectional area of 24.5 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 135 cm³, and the elastic modulus Wel,y is 104 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 48 kNm before any stability check.

The second moment of area about the major axis, Iy, is 920 cm⁴, and about the minor axis Iz is 920 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 6.13 cm about the major axis and iz is 6.13 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 6.13 cm a 0.6 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 1,841 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.