Composite action — where it appears
Named by 4 essays across 4 fields — each of them below, with the objects they name alongside it.
The structure that was never complete
Every analysis in this collection is of a finished structure loaded once. Real ones are built in pieces, and each piece carries whatever was present at the moment it became structural — so the stress in a member depends on when it arrived, which appears nowhere on any drawing.
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.
Two beams, or one beam four times as stiff
Stack two planks and they bend as two beams whose faces slide past one another. Bond the faces and the pair has one neutral axis, four times the second moment and half the stress. Nothing was added but a restraint on slip.
A section made of two materials, one of them pretended away
Multiplying a material's width by the ratio of the moduli produces a fictitious section of one material with the right neutral axis and the right forces. It is not a trick — it is compatibility and Hooke's law written down — and it says a stiff material takes what its modulus asks for.
Named alongside it
The objects these essays reach for when they reach for this one.
CreepSuperpositionConstruction sequenceNeutral axisPlane sectionsProppingSecond moment of areaBuilt up sectionCentroidContinuityCracked sectionDeflection