Structural Engineering & Statics
where the load goes
Concept

Interaction — where it appears

What two actions do to a section together, which is never the sum of what each does alone and is drawn as a curve rather than a sum.

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

00.20.40.60.8100.20.40.60.81moment ÷ plastic momentaxial force ÷ squash loadrectangle: 25.0% of Mp outside the lineI-section: 6.0% of Mp outside the linethe straight-line rule

Two ways to fail, and the curve between them

A column carrying both compression and bending has two capacities and a rule for sharing them out. The rule is a straight line, the truth is a curve, and for a rectangle the straight line gives away a quarter of the plastic moment at half the squash load.

materials · interaction wall 146 mmframe 140 mmtogether 58 mm20 storeys at 3.5 m · 40 kN per floor

How a tall building stands still

A shear wall bends and a framed tube shears, and the two deflected shapes are the wrong way up for each other. Tie them together at every floor and the pair is stiffer than the sum of their stiffnesses — because near the base the wall holds the frame back and near the top the frame holds the wall.

structures · lateral system

Named alongside it

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

EccentricityEqual area axisFree bodyIndeterminacyLateral systemNeutral axisOutriggerPlastic momentPlastic neutral axisSection shapeShear wallSquash load

All concepts