Structural Engineering & Statics
where the load goes
Concept

Catenary — where it appears

The hanging shape a cable takes under its own weight, and the mechanism a floor falls back on when it has lost its support.

Named by 3 essays across 2 fields — each of them below, with the objects they name alongside it.

cable: pure tensionreflected herearch: pure compression

The shape that carries itself, and the arch that is its reflection

Hang a chain and it takes the one shape that carries its load in pure tension. Turn the shape upside down and it carries the same load in pure compression. That is what an arch is.

structures · funicular 00.511.522.5020406080100120140deflection ÷ thicknessload the strip carriesarchingcatenaryyield line× 3.89 at 0.24tnothing to arch against

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.

internal-forces · membrane action the cable alonekink of 0.0083 radwith the stiffening girderthe cable takes 83% of the load; the girder spreads it over 183 mμ = L√(H/EI) = 4.93

The deck is not there to carry the load

A cable takes the shape of whatever is on it, which is exactly the problem — under a point load its shape is a kink, and a kink is not a road. The stiffening girder exists to spread the load until what reaches the cable is something the cable's own shape is right for.

structures · stiffening girder

Named alongside it

The objects these essays reach for when they reach for this one.

Horizontal thrustForm findingFunicularSag ratioAlternative load pathCharacteristic lengthCollapse mechanismCompatibilityDeflectionElastic foundationGeometric nonlinearityLimit point

All concepts