10-10-2014, 02:10 PM
The earthquake induced lateral forces on a structure, computed on the
assumption that its base is bonded to the supporting soil, produce an
overturning moment which may exceed the available overturning resistance due
to dead weight, with the result a portion of the base of the structure would
uplift temporarily. This phenomenon of partial separation of the base of a
structure from the supporting soil during strong earthquakes has be6n observed
in the past and widely reported in the literature.
The objective of this study is to investigate the effect of the lift-off-on the
response of a nuclear Reactor structure resting on rock. The Reactor structure is
idealized as a lumped mass system with ten degrees of freedom. . The
supporting soil is represented by a Winkler model with spring-damper elements
distributed uniformly. It is assumed that the springs can not take tension
implying that lift.-off takes place when the upward displacement of a portion of
the base is greater than the initial static deflection. The flexibility coefficients of
the structure are determined by beam theory accounting for flexural and shear
deformations.