Structural Engineering & Statics
where the load goes
Concept

Spandrel — where it appears

The beam running between perimeter columns at each floor of a framed tube or a moment frame. Its stiffness sets the racking stiffness of the whole perimeter and therefore how evenly axial force is shared across a face, which makes it the member a designer moves to control shear lag.

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

20%40%60%80%100%020406080100120torsional stiffness left, as a fraction of the uncracked valuetorque in the spandrel (kNm)compatibilityit goes awayequilibriumit does not100 kNm40 kNmcracking sheds a factor of 2.47 of torque, and the floor beam pays 18% more sagging moment

The torsion that goes away if you let it

A spandrel beam attracts a torque in proportion to its own torsional stiffness. Crack it and the stiffness falls by a factor of four, the torque falls with it, and nothing has failed — because the floor beam it was competing with picks up exactly what was shed. A canopy hung off the same spandrel is a different animal entirely.

internal-forces · compatibility torsion -15-10-551015020406080across the face (m from the centre)column stress (N/mm²)11 columns at 3.0 mcorner 69.418.2 in the middleplane sectionseffective width 51% · stiffness 72% of gross

The corner columns take more than their share

A framed tube is a hollow cantilever, and a hollow cantilever's flange ought to be uniformly stressed. It is not, and the reason is that the only route the axial force has into a column in the middle of a face is the in-plane shear of the frame — one bay at a time, from the corner inwards.

structures · framed tube

Named alongside it

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

BracingCantileverCompatibility torsionCorner columnCracked sectionDistribution factorDriftEffective widthEquilibrium torsionFixed end momentFramed tubeJoint stiffness

All concepts