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RHS 300×100×7.1 - Section Properties

The RHS 300×100×7.1 is a rectangular hollow section with a mass of 42.6 kg/m, an overall depth of 300 mm and width of 100 mm and a wall thickness of 7.1 mm. It has a cross-sectional area of 54.2 cm², a second moment of area Iᵧ of 5680 cm⁴, a plastic modulus Wₚₗ,ᵧ of 490 cm³, tabulated by CivilAxis from BS EN 10210-2:2006 (SCI P363 Blue Book).

Mass
42.6 kg/m
Depth
300 mm
Width
100 mm
Wall thickness
7.1 mm
Area
54.2 cm²
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RHS Hot-finished section profile showing the dimension symbols used for RHS 300×100×7.1

Dimension symbols for RHS Hot-finished sections. Not to scale.

RHS 300×100×7.1 section properties to BS EN 10210-2:2006.

Geometry

Depth of sectionh300
Width of sectionb100
Wall thicknesst7.1

Mass and area

Mass per metremass42.6
Cross-sectional areaA54.2

Bending about the major axis (y-y)

Area moment of inertia about y-axisIy5680
Elastic section modulus about y-axisWel,y379
Plastic section modulus about y-axisWpl,y490
Radius of gyration about y-axisiy10.2

Bending about the minor axis (z-z)

Area moment of inertia about z-axisIz981
Elastic section modulus about z-axisWel,z196
Plastic section modulus about z-axisWpl,z221
Radius of gyration about z-axisiz4.25

Torsion and warping

Torsion constant (St Venant)It2780
Section modulus for torsionWt352

Classification and stability

Flange local-buckling ratiocf/tf11.1
Web local-buckling ratiocw/tw39.3

Surface area

Surface area per metreSA/m0.782
Surface area per tonneSA/t18.4m²/t

Is RHS 300×100×7.1 strong enough?

Simply supported beam, uniform load, major-axis bending - to EN 1993-1-1.

✅Passes - 59% utilised, deflection governs
Bending27%
47.3 / 173.9 kNm
Shear4%
31.5 / 833.2 kN
Deflection59%
9.9 / 16.7 mm

Class 1 section. ULS uses γQ = 1.5 on the load you enter; deflection uses the unfactored load against L/360. Lateral-torsional buckling is not included - the compression flange is assumed restrained.

Common questions about RHS 300×100×7.1

RHS 300×100×7.1 has a mass of 42.6 kg/m, tabulated to BS EN 10210-2:2006. A 12 m length therefore weighs about 511 kg, which is the figure to use for a steel take-off or when checking a lift.

RHS 300×100×7.1 has a depth of 300 mm, a width of 100 mm, a wall thickness of 7.1 mm, with a cross-sectional area of 54.2 cm². These are the nominal dimensions from BS EN 10210-2:2006; rolling tolerances apply to the delivered section.

The plastic section modulus about the major axis, Wpl,y, is 490 cm³, and the elastic modulus Wel,y is 379 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 174 kNm before any stability check.

The second moment of area about the major axis, Iy, is 5,680 cm⁴, and about the minor axis Iz is 981 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.

Its local-buckling ratios are cf/tf = 11.1 for the flange and cw/tw = 39.3 for the web. EN 1993-1-1 Table 5.2 compares these against limits scaled by epsilon = sqrt(235/f_y), so the class depends on the steel grade as well as the geometry - the same section can be Class 1 in S275 and Class 3 in S355. Use the Capacity tab on this page for the classification at a specific grade.

iy is 10.2 cm about the major axis and iz is 4.25 cm about the minor axis. Column buckling is governed by the SMALLER value: the slenderness is lambda = L_cr / i, so with iz = 4.25 cm a 0.4 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 2,780 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.

Related RHS Hot-finished sizes

RHS 260×140×14.2RHS 260×140×16RHS 300×100×5RHS 300×100×6.3RHS 300×100×8RHS 300×100×8.8RHS 300×100×10RHS 300×100×12.5

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