Structural Engineering & Statics
where the load goes
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Scale changes everything — page 2

Essays 25 to 26 of 26 on this thread, in the same order.
1234403020100-10-20-30-40stage in the beam's lifeshape (mm, sag positive)against noneagainst wetagainst deadagainst total Deflection

Built to the wrong shape on purpose

A cambered beam is fabricated curved upward so that load bends it down to something like straight. Nothing in the analysis changes, no stress anywhere is altered, and almost every mistake made with it is a bookkeeping mistake about which loads count.

 flat: I = 6750 mm⁴folded: I = 67.50×10⁶ mm⁴300gain 10000× = (100)²limited by buckling of the leg: the leg goes at 27 N/mm² Structural form

Folded until it spans

A flat sheet has a second moment of area of B·t³/12 and will not span anything. Folded, the same material has B·t·h²/12, and the gain is exactly the fold depth over the thickness, squared — a ratio with no material in it and no width in it.

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