| Abstract: | The dynamic behaviour of a simplified model of a multi-storey building, supported by an elastic foundation and allowed to uplift, is examined. The building is modelled by an n-degree-of-freedom oscillator, while the foundation is represented by a viscously damped two-spring model which permits uplift. This model has been shown in previous studies to be an accurate approximation to the more realistic but more complex Winkler foundation. Approximate values for the characteristic frequencies of the interacting system are presented and a simple, first-mode solution is developed. The response of the system is non-linear and the apparent fundamental period increases with the amount of lift-off. In contrast to the first mode of the superstructure which participates strongly in the interaction, the second and higher modes of the building are not affected significantly by either the interaction with the soil or the uplift. The study shows that lift-off results in larger rocking motion of the structure, but it is not clear from the analysis and the example whether the interfloor displacements are consistently increased or decreased, since this appears to depend on the properties of the system and the excitation. |
