Yield line — where it appears
The slab that spans both ways
A panel supported on four sides sends its load in two directions at once, and the share is decided by a fourth power — so a panel a third longer than it is wide has already stopped being a two-way slab in any useful sense. What it does at collapse is a different calculation with a different answer.
The force nobody put in the model
A slab strip whose ends cannot move apart is not the strip in the yield-line calculation. Deflecting shortens the chord between its ends, the ends do not come in, and the strip is forced into an arch — worth four times the load it was designed for, at a movement nobody would see.
Named alongside it
The objects these essays reach for when they reach for this one.
Collapse mechanismAlternative load pathCatenaryCompatibilityHorizontal thrustLimit pointLoad pathMembrane actionNo tension materialPlastic hingeProgressive collapseRestraint