Structural Engineering & Statics
where the load goes
Concept

Proof stress — where it appears

4 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
00.5%1%2%2%0100200300400500600strainstress, N/mm²the 0.2% proof stress: 460 N/mm²mild steelhigh-strength steelaluminium

The stress at which nothing in particular happens

One material in six has a yield point that a specimen actually does something at. For all the others the yield stress is a construction — a line drawn at an arbitrary offset — and every calculation on this site depends on it.

materials · proof stress 00.1%0.2%0.3%0.4%0.5%0.6%050100150200250300350strainstress, N/mm²mild steelaluminiumconcretetimber

The one number a stronger steel does not change

Geometry beats material almost everywhere on this site. Stiffness is the exception in the other direction — it cannot be bought at all, because every steel ever made has the same elastic modulus.

materials · elastic modulus neutral axisI-sectionstrainalways a straight linestressthe material's own curve, sidewaysC = 322.5 kN · T = 322.5 kN · lever arm 180 mm · M = 58.1 kNm0% of the area has yielded — 0 mm from the top, 0 mm from the bottom · Mp = 72.6 kNm · shape factor 1.09

The stress that was there before the load

A rolled steel section leaves the mill carrying eighty N/mm² of stress with nothing applied to it, in a pattern that sums to no force and no moment. It is invisible to every calculation and it is the knee in every column curve.

materials · residual stress 20040060080000.20.40.60.81temperature, °Cfraction of the cold valuestrength runs out at 558°Cstiffness at 500°Cyield stresselastic modulusworking at 60% of cold capacity

The hour that is really a temperature

A fire rating is quoted in minutes and there is no time in the physics anywhere. What decides is a temperature, and the stiffness reaches its limit sixty degrees before the strength does — so the way a member fails can change while it is burning.

materials · fire

Named alongside it

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

Elastic modulusBucklingStress strainColumn curveConstitutive lawCreepCritical temperatureDuctilityFireFirst yieldIdealisationImperfection

All concepts