Gravity Load and Vertical Ground Motion Effects on Earthquake Response of Simple Yielding Systems

Computed responses of idealized one-story yielding systems to earthquake ground motion are presented with the objective of evaluating the effects of gravity loads and vertical ground motions. These results demonstrate that the coupling between lateral and vertical deformations created by yielding in the system must be considered in order to predict the plastic part of vertical deformations due to horizontal ground motion. However, simpler analysis without such deformation coupling, but with reduction of lateral yield strength due to gravity load, would generally be satisfactory for predicting the lateral response of the system. The principal effect of the vertical component of ground motion is to superpose elastic vertical oscillations about the gradually growing vertical deformation that resulted from yielding due to horizontal ground motion alone. Lateral deformations are not influenced significantly by vertical ground motion; thus they may be determined from analysis of response to horizontal ground motion only.