RND 40 - Section Properties

RND 40 has a mass of 9.86 kg/m, tabulated to EN 10058. A 12 m length therefore weighs about 118 kg, which is the figure to use for a steel take-off or when checking a lift.

The plastic section modulus about the major axis, Wpl,y, is 10.67 cm³, and the elastic modulus Wel,y is 6.283 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 4 kNm before any stability check.

The second moment of area about the major axis, Iy, is 12.57 cm⁴, and about the minor axis Iz is 12.57 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 1 cm about the major axis and iz is 1 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 1 cm a 0.1 m effective length already gives lambda = 100. Minor-axis buckling almost always controls unless the weak axis is restrained.