Base shear — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
Also named here as response spectrum — the same set of essays touches all of them, so they are one junction rather than several.
Most of the mass moves together
A sixteen-storey frame has sixteen modes, and the first one carries eighty-four per cent of the mass. That is why a hand calculation on one mode gets the base shear right to within a tenth — and why the same calculation gets the acceleration at roof level wrong by a factor of two.
The spectrum is not a load
A response spectrum looks like a load curve and is not one. Every point on it is the peak of a complete time integration of one particular structure, and the curve is what you get by doing that again for every structure there could be.
Named alongside it
The objects these essays reach for when they reach for this one.
Response spectrumDampingDesign spectrumFloor accelerationGround motionModal analysisModal massMode shapeNatural periodParticipation factorPseudo accelerationSeismic mass