Structural Engineering & Statics
where the load goes
Concept

Shell — where it appears

A curved surface thin enough to carry load in its own plane rather than across it. The curvature supplies the structural depth, so a shell needs a fraction of a flat plate's thickness for the same span — and presents the whole of the bill at its edges.

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

NN2R = 0.60 m — the projected widthp = 1 MPap · 2R = 2N ⇒ N = pR = 300 kN/mno thickness in it, no second moment, no length

The force that is only a radius

Every internal force in this collection arrives with a lever arm attached. A hoop force does not. Cut a cylinder along a diameter and the free body settles it in one line — pressure times radius, with no thickness, no second moment and no length in it — which is why a tank wall is thin and why its worst hoop force is not at the bottom.

internal-forces · hoop tension pinneda mechanismno shear stiffness at allrigid1205 mmGt = 0.35% of a sheet'sbraced6.4 mmGt = 65% of a sheet'striangulated4.3 mmGt = 98% of a sheet's

A shell only if the grid takes shear

A curved surface carries load in its own plane at a fraction of the material a flat one needs, and every gridshell ever built is an attempt to buy that with members instead of with a surface. The attempt succeeds or fails on one property nobody draws — whether four bars meeting at a corner can resist being racked — and a pinned quadrilateral grid cannot resist it at all.

structures · gridshell

Named alongside it

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

Internal forcesMembrane actionBending momentBoundary layerBracingBucklingCrack controlDomeEquilibriumEquivalent continuumFree bodyGridshell

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