Why steel beams are shaped like an I: the same steel, 25 times stiffer
30seconds
Put a beam across a gap and it sags: the top edge is squeezed, the bottom stretched, and the steel in the middle does almost nothing. That is why girders are shaped like an I.
The stiffness of a beam grows with the cube of its depth. Reshape the same 4,000 mm² of steel yourself: drag the depth and flange width, or flip between a plank, a square bar and an I-beam. Watch the sag shrink while the weight stays exactly the same, and see why you cannot just keep thinning the web.
Deep dive · 4 min
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