HSS 3-1-2X2-1-2X3-8 - Section Properties

HSS 3-1-2X2-1-2X3-8 has a mass of 12.17 lb/ft (18.1 kg/m), tabulated to AISC Shapes Database v16.0. A 12 m length therefore weighs about 217 kg, which is the figure to use for a steel take-off or when checking a lift.

HSS 3-1-2X2-1-2X3-8 has a depth of 3.5 in (88.9 mm), a width of 2.5 in (63.5 mm), a web thickness of 0.349 in (8.9 mm), a wall thickness of 0.349 in (8.9 mm), with a cross-sectional area of 3.39 in² (21.9 cm²). These are the nominal dimensions from AISC Shapes Database v16.0; rolling tolerances apply to the delivered section.

The plastic section modulus about the major axis, Wpl,y, is 58.83 cm³, and the elastic modulus Wel,y is 44.573 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 21 kNm before any stability check.

The second moment of area about the major axis, Iy, is 197.7 cm⁴, and about the minor axis Iz is 115.3 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 3 cm about the major axis and iz is 2.3 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 2.3 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 256.4 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.