A single-degree of freedom rigid framed structure with variable loading is studied under the influence of five artificial earthquakes applied directly by use of the lumped-impulse numerical integration method and indirectly by converting the psuedo-accelero-grams of the artificial earthquakes into a half range sine expansion of the Fourier series by harmonic analysis. A comparison of the results obtained by each method is made for (a) an elastic system with no damping, (b) an elastic system with ten per cent of critical damping, and (c) an elasto-plastic system with ten per cent of critical damping. The objective of this study was to find through harmonic analysis a method to predict the approximate deflections of structures that might be caused by major earthquakes. It was found that the randomness of motion expressed by the psuedo-accelerograms does not permit generalizing the results of the harmonic analysis. / Master of Science