Structural Engineering & Statics
where the load goes
Concept

Tall building — where it appears

A building high enough that the fourth power in its drift, rather than any strength, decides how much material its lateral system takes. Its lateral system is sized by drift and its comfort by acceleration, so the two quantities that decide it are both serviceability ones.

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

-40-30-20-10010020406080100120140column shorter than core (mm)height (m)from loadfrom shrinkagethe sumworst 43 mmat level 40one in 208

The columns are shorter than the core

Every column in a tall building gets shorter as the building is built on top of it, and the core beside it gets shorter by a different amount. The floors between them tilt by the difference — and the difference is largest exactly half way up, because a floor near the top has almost nothing built above it and a floor near the bottom has almost nothing beneath it.

deflection · differential shortening 294 kN294 kNoutrigger · 35 MNm30 kN/mtop drift 74 mmwas 360 mmbase moment 38 MNmwas 74

The arm that makes the columns work

The perimeter columns of a tall building are already there, already carrying gravity, and already the furthest thing from the centre. They take almost none of the overturning, because a floor slab transmits shear and not moment — and one storey-deep arm at the right height changes that by nearly a half.

structures · outrigger

Named alongside it

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

CoreDifferential shorteningAxial shorteningCompatibilityCompensationConstruction sequenceCreepDriftElastic modulusImposed deformationLateral systemOptimisation

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