The Earthquake Engineering Online Archive

Effects of transient foundation uplift on earthquake response of structures

Yim, Chik-Sing; Chopra, Anil K.

UCB/EERC-83/09, Earthquake Engineering Research Center, University of California, Berkeley, 1983-06, 137 pages (485/Y55/1983)

The objective of this study is to develop a better understanding of the effects of transient foundation uplift on response of structures, so that the related reduction in earthquake forces can be considered in design of structures. The mathematical models chosen are simple, but incorporate the most important effects of soil flexibility and realistic mechanics of uplifting and impact. In its fixed condition, the structure itself is idealized as a single degree-of-freedom system attached to a flexibly supported rigid foundation mat. The flexibility and damping of the supporting soil are represented by two alternative idealizations: (1) two spring-damper elements, one at each edge of the foundation mat, or (2) Winkler foundation with spring-damper elements distributed over the entire width of the foundation mat. Response spectra are presented, in which for each set of system parameters the maximum base shear is plotted against the natural vibration period of the corresponding rigidly supported structure for two conditions of contact between the foundation mat and the supporting spring-damper elements: (a) bonded contact preventing uplift and (b) unbonded contact with uplift permitted. Because foundation uplift is shown to reduce the structural deformations and forces, there is no need to prevent it but, on the contrary, it is desirable to permit it.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-83-09.pdf (5 MB)