Nonlinear response of continuous systems subjected to base excitation

An empirical investigation into the non-linear response of continuous systems resting on viscoelastic foundations, being excited from the base. This applies to the better dynamic understanding of building structures excited by earthquakes, or indeed any structure excited from the base. The partial differential equations describing the lateral vibration of the system were first reduced to a set of N nonlinear ordinary differential equations by use of the Normal Mode Summation method. A transformation of the dependent variable allowed these equations to be expressed in a form by which the averaging method of Krylov and Bogoliubov could be applied to obtain an analytical solution. The Krylov-Bogoliubov theorem is a mathematical method for approximate analysis of oscillating processes in non-linear mechanics. Two cases od a beam problem were analysed; simply-supported and free-free. These were analysed for some typical foundation nonlinearities with the base excitation in the form of step and pulse functions. Closed form solutions for the amplitude and frequency variations were obtained in almost all case and results were presented for the various nonlinearities and excitations. The maximum stress levels experienced by the two beam modes were also calculated. A numerical analysis was conducted and included in the text for comparison with that obtained from the Krylov-Bogoliubov theorem. Special thanks to Professor Subash C Sinha for support and guidance in this paper.