Structural Engineering & Statics
where the load goes
Concept

Secondary stress — where it appears

A stress arising from restrained deformation or from an idealisation the structure does not obey, rather than from equilibrium with the applied load. It relaxes as soon as the structure yields or cracks, which is why it is checked against different limits from a primary stress.

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

A Pratt truss of 8 panels. A Pratt truss under equal panel-point loads. The joint equilibrium equations were assembled and solved; 14 members came out in tension, 13 in compression and 2 carrying nothing.

Halving the panel buys a shorter strut

Subdividing a truss into more panels of the same span and depth barely changes the chord forces, because the couple that carries the moment has not moved. What it changes is the length of every compression member, and a buckling capacity goes as the inverse square of a length.

structures · Truss 3 continuous spans against 3 simple ones. The bending moment in a continuous beam, solved by the stiffness method, drawn over the moment in the same spans made simply supported. The peak sagging moment falls from 28.1 to 18.0, and a hogging moment of 22.5 appears over the supports where there was none.

The chord is a continuous beam

A truss analysis reports one number per member, and for a chord running through eight panels that number is an axial force with no bending in it. The chord is a single piece of steel spanning between its own nodes, and anything landing between them bends it.

structures · Truss

Named alongside it

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

Chord forcePanel pointTrussBending momentBucklingCompressionConnectionContinuityEffective lengthFree momentInteractionLever arm

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