Fig. 5 shows different sections of metal available from a stockist. The sections are shown as cross-sectional views. The metal has been selected for its spe...

(a) The stock form shown at C is a channel (also called U-channel or C-section). [1]

The cross-section shows a U-shaped profile: a flat base (web) with two upstanding flanges. Channel section is commonly used in structural steelwork for framing, shelving brackets, and supports where one open side is acceptable or where other components slot into the channel.

(b) The stock form shown at D is an I-beam (also called I-section or RSJ - rolled steel joist). [1]

The cross-section shows a central vertical web with horizontal flanges at both top and bottom, forming the characteristic I shape.

(c) An I-beam has a much greater resistance to bending (higher stiffness) than a flat bar of the same weight of material. [1] This is because the material is concentrated at the top and bottom flanges, positioned as far as possible from the neutral axis (the centre of the cross-section). In bending, the highest stresses occur at the outermost surfaces. By placing material where stress is greatest and removing it from the centre where stress is lowest, the I-beam uses material far more efficiently. A flat bar distributes its material uniformly across a thin cross-section, so most of the material contributes little to bending resistance. For horizontal shelf supports that must carry heavy loads without sagging, the I-beam provides a stronger, lighter solution. [1]