Maximum Modal Response
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Let Sd(ωI, ξI), Sv(ωI, ξI), and Sa(ωI, ξI) be the input response spectra values for the displacement, pseudo-velocity, and pseudo-acceleration, respectively. As each mode can be idealized as a SDOF system, the maximum responses over excitation duration in terms of modal coordinates are obtained from the input response spectra values:
are the modal relative displacements,
the modal relative velocities, and
the modal absolute accelerations.
Γi is the modal participation factor for each mode i, which is equal to .
is the transpose of eigenvector i.
, which is an influence vector that relates the base motion to the rigid body structure displacements.
For each mode, the structure's maximum responses in relation to the modal coordinates are:
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