Structural Engineering & Statics
where the load goes
Concept

Prestress losses — where it appears

The part of a prestressing force that is no longer there when the structure is in service, from relaxation, creep, shrinkage, friction and elastic shortening. They are estimates rather than measurements, and they are why a prestressed section has to be checked in two states rather than one.

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

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

prestress alone-6.3320.61tensionat transfer-2.4716.76tensionin service7.613.82with no prestress12.67-12.67tension

The load put on backwards

Every other structure in this collection waits for its load and then resists it. A prestressed one is given a load first — chosen, permanent, and pointing the wrong way — so that when the real one arrives the two nearly cancel and the material never has to do the thing it is bad at.

internal-forces · prestress 0501001502002503003504000.00.10.20.30.40.50.6eccentricity below the centroid (mm)10⁶ ÷ P (so lower is more prestress)transfer, toptransfer, bottomservice, topservice, bottom1029 kNthe kernthe wedge runs from e = 0 to 400 mm

Four inequalities and a wedge

A prestressed section has to satisfy two stress limits when the force is largest and the load smallest, and two more when the force has relaxed and the load has arrived. Each is linear in one over the force — which turns a search for a prestress into a region on a page, and turns an impossible section into an empty one.

sections · prestress limits

Named alongside it

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

Bending stressCrackingKernPrestressTransferCoverCreepEccentricityFeasible regionLoad balancingMagnel diagramRelaxation

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