A steel section table looks dense, but every column answers one practical question: will this beam carry the load, and how heavy is it? Here is what each symbol means and which check it feeds.
The geometry columns
- Mass (kg/m) - what you pay for and what dead load you add. Steel cost tracks mass directly.
- Depth h and width b (mm) - the overall envelope. Depth drives stiffness; width affects lateral stability and where bolts can land.
- Web tw and flange tf thickness (mm) - thickness sets the section class (how much of the capacity you can actually use before local buckling), and matters for welding and bearing.
The strength columns - and the check each one is for
- Second moment of area, Iy and Iz (cm⁴) - resistance to bending and the basis of deflection. Bigger Iy, less sag. The subscript is the axis: y is the strong (major) axis, z the weak (minor) axis.
- Elastic section modulus, Wel (cm³) - for the elastic moment check M / Wel ≤ fy. Use it when the section can't fully yield (slender, Class 3).
- Plastic section modulus, Wpl (cm³) - for the plastic moment resistance of a compact (Class 1/2) section: Mpl = Wpl · fy. Always larger than Wel; the ratio Wpl/Wel is the shape factor.
- Radius of gyration, iy and iz (cm) - the buckling parameter. Slenderness is λ = L / i, so the smaller radius (usually iz) governs column buckling.
Worked example: reading IPE 330
From the IPE 330 reference page: mass 49.1 kg/m, depth 330 mm, Iy = 11800 cm⁴, Wpl,y = 804 cm³. For S355 steel the plastic moment about the major axis is roughly:
That single line is what the whole table exists to give you.
The habit that prevents mistakes
Always check the axis subscript before you use a value. Designing a beam bending the strong way but accidentally picking the z (weak-axis) modulus is one of the most common - and most dangerous - reading errors. When in doubt, open the full section tables and confirm which axis the load is about.