Structural Engineering & Statics
where the load goes
Generator

The body-stability generator

Rendered here at the parameters it defaults to, with every essay that calls it — which is the same list as the blast radius of changing it.
Weight is the only thing holding it downA body 4 m wide and 12 m tall weighing 900 kN, under a wind pressure of 1 kN/m². The wind delivers 36 kN and an overturning moment of 216 kNm about the leeward toe; the weight restores 1800 kNm, a factor of 8.33. The resultant lands 0.24 m from the centre against a middle third of ±0.67 m, so the base is still wholly in bearing.36 kNW = 900 kNmiddle third: ±0.67 mresultant at 0.24 mrestoring 1800 kNmoverturning 216 kNmfactor 8.33

Weight is the only thing holding it down. A body 4 m wide and 12 m tall weighing 900 kN, under a wind pressure of 1 kN/m². The wind delivers 36 kN and an overturning moment of 216 kNm about the leeward toe; the weight restores 1800 kNm, a factor of 8.33. The resultant lands 0.24 m from the centre against a middle third of ±0.67 m, so the base is still wholly in bearing.

3 essays call body-stability. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.

Where it is called

Changing this generator changes every one of these figures.

48 kNW = 120 kNmiddle third: ±0.42 mresultant at 1.20 mrestoring 150 kNmoverturning 144 kNmfactor 1.04 Equilibrium

Weight is the only thing resisting it

A structure that is strong enough everywhere can still be blown over, and nothing in its material properties has any part in whether it is. The whole answer is a weight and a width — and the failure begins long before anything tips, at the moment one edge stops pressing down.

 rectangle±100 of 600 mm33.3% of the depth Sections and stress

The middle third

A material that cannot be pulled imposes a condition on where the load may land, and the condition is a region rather than a point. For a rectangle it is the famous middle third; for every other section it is a shape nobody quotes, and one ordinary section's is nearly twice as generous as the rule allows.

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

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.

The library, page 1 of 5 — where body-stability sits