Structural Engineering & Statics
where the load goes
Concept

Tendon profile — where it appears

The line a prestressing tendon takes along a member, chosen so that its curvature produces an upward load where the applied load acts downward. It is constrained by cover at mid-span and by the end block at the anchorage, and the two limits pull in opposite directions.

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

05101520-600-400-200200400distance along the beam (m)bending moment (kNm)primarysecondarythe loadeverythingpushed down by 51.0 kN with nothing applied at all

The prestress that pushes back

On a simply supported beam a tendon is an internal matter and changes no reaction. Put the same beam on three supports and the tendon lifts it off the middle one, the support refuses, and the force it takes to hold the beam down is a reaction produced with no load applied at all.

internal-forces · secondary 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.

EccentricityPrestressBending stressConcordant profileContinuityCoverCrackingCreepEquivalent loadFeasible regionIndeterminacyKern

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