Structural Engineering & Statics
where the load goes
Concept

Cover — where it appears

The thickness of concrete between a reinforcing bar and the nearest face. It sets how long a carbonation or chloride front takes to reach the steel, as a square of itself, and it sets the pressure the surrounding concrete can take before a corroding bar splits it.

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

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 204060800102030405060cover (mm)years to a split coverinitiation ∝ c²and propagation35 mm: 9.1 yr70 mm: 36.2 yrthe cover splits at a section loss of 0.21%

The load that comes from inside

Every action in this collection has been applied from outside — a weight, a pressure, a movement, a temperature. Corrosion is not applied at all, and the reason it belongs to statics rather than to durability is that what does the damage is a load: rust occupies three times the volume of the steel it came from, and the only place to make room is by pushing the cover apart.

materials · corrosion

Named alongside it

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

PrestressAnchorageBending stressBondCorrosionCrack widthCrackingCreepDiffusionDurabilityEccentricityExpansion

All concepts