Structural Engineering & Statics
where the load goes
Concept

Deep beam — where it appears

A member too deep for its span to contain any region where a section calculation is legitimate, so its whole length is disturbed.

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

Also named here as strut and tie — the same set of essays touches all of them, so they are one junction rather than several.

span ÷ depth = 8plane sections holdspan ÷ depth = 4plane sections holdspan ÷ depth = 2off by 19%span ÷ depth = 1off by 31%the assumption is the theory — everything else is arithmetic on top of it

Plane sections stay plane, and what the assumption costs

Beam theory rests on one sentence about geometry. It is very nearly true for a slender member, wrong for a deep one, and everything in the subject that fails does so where it stops holding.

sections · plane sections 1200 kNtie 750 kNstrut 960 kN38.7°z = 1600strut 3.0 N/mm² over 812 mm · limit 15.8bursting across each strut 240 kN · tie steel 1724 mm²

When there is no section to design

Beam theory needs a section, and a section needs the strain to be linear across it. Within about a depth of a support, a load, a corner or a hole it is not — and those are the regions structures actually fail in.

internal-forces · strut and tie

Named alongside it

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

Plane sectionsSaint-Venant's principleStrut and tieDisturbed regionEquilibriumIdealisationLoad pathLower bound theoremNeutral axisSafe theoremSpan to depth ratioStrain distribution

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