NEHRP Clearinghouse

Title
Dynamic Behavior of Rocking Stuctures Allowed to Uplift.
File
PB82212945.pdf
Author(s)
Psycharis, I. N.
Source
National Science Foundation, Washington, DC., January 1982, 238 p.
Identifying Number(s)
EERL-81-02
Abstract
This report studies the phenomenon of uplifting, the partial separation of the base of a structure from its foundation, which occurs during the ground-shaking of an earthquake. The cases of both a rigid superstructure and a multistory building are considered. Two foundation models which permit uplift are used: the Winkler foundation model, and the much simpler, two-spring foundation model. Simple approximate methods for calculation of the apparent fundamental period of the rocking systems are developed and simplified methods of analysis are proposed. Because uplift leads to a softer vibrating system which behaves nonlinearly, the apparent fundamental resonant frequency of the uplifting system is always less than the fundamental resonant frequency of both the soil-structure interacting system, in which lift-off is not allowed, and the superstructure itself. The second and higher resonant frequencies of the superstructure are not significantly affected by the lift-off. For damped foundations, the ratio of critical damping associated with the apparent fundamental mode decreases with the amount of lift-off.
Keywords
Dynamic response; Buildings; Theses; Earthquake engineering; Earthquakes; Foundations; Soil structure interactions; Vibration damping; Uplift pressure; Mathematical models; Dynamic structural analysis