17.3.5 Inelastic Response Spectra

While the foregoing discussion has been for elastic response spectra, most structures are not expected, or even designed, to remain elastic under strong ground motions. Rather, structures are expected to enter the inelastic region — the extent to which they behave inelastically can be defined by the ductility factor, m:

My where Mm is the actual displacement of the mass under actual ground motions and My is the displacement at yield (i.e., that displacement which defines the extreme of elastic behavior). Inelastic response spectra can be calculated in the time domain by direct integration, analogous to elastic response spectra but with the structural stiffness as a nonlinear function of displacement, k = k(u). If elastoplastic

Response spectrum

Imperial Valley Earthquake May 18, 1940—2037 PST

III A001 40.001.0 El Centro site Imperial Valley Irrigation District Comp S0° E Damping Values are 0, 2, 5, 10, and 20% of critical

0 0

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