Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 427

Advances in Seismic Design Methodologies 427

Effects ofsuperior vibration modes

Base Shear(kN)

Drift
Figure 9.26 Influence of superior vibration modes due to the changing of structural
properties (after Pinho, 2007)

Therefore, the results obtained using the push-over method demonstrate that it is a
very useful one, but not an infallible tool for assessing inelastic strength and
deformation demands and for exposing the design weaknesses. On the positive side,
the method provides good estimations of global as well as local inelastic deformation
demands for structures which primarily vibrate in the fundamental mode. On the
negative side, deformation estimates obtained from a push-over analysis may be
grossly inaccurate for structures where higher mode effects are significant (Figure
9.27). This problem can be mitigated by applying more than one load pattern, including
load patterns, which account for higher mode effects. Even with the application of
multiple load patterns, this analysis could provide misleading results (Lawson et al,
1994).