Concept
Statical determinacy — where it appears
2 essays name this object, across 2 fields. What follows is each of them, and the objects they name alongside it.
Bending that arrives as twist
A straight beam under a vertical load carries no torsion unless something applies one. A beam whose axis curves on plan carries torsion everywhere, from the same load, with nothing applied off the axis — and it cannot be simply supported at all.
Three equations at every joint
A plane truss is determinate when m + r = 2j. A space frame needs 3j, and that one changed digit is why a cube of twelve bars is six mechanisms short while looking perfectly solid — and why every three-dimensional frame ever built is made of triangles in several planes at once.
Named alongside it
The objects these essays reach for when they reach for this one.
MechanismBending momentCompatibilityCurved in planDouble layer gridEquilibrium matrixFree bodyLoad pathLoad sharingMatrix rankMaxwell ruleMoment vector