Vibrations of railway bridges for high speed trains under moving loads varying in time

Experimental measurements show that the loads transmitted from train axles contain not only a constant component, but also significant alternating components in the range 0-6Hz. Using the model of a simply supported beam transited by moving loads varying in time, the authors analyse the deflection produced in small and medium span bridges under the action of combined loads. A first case is the deflection under the combined load owing to a constant component together with an alternating component and transmitted by a single axle, while a second case is the study of the combined action of several composite loads transmitted by equidistantly spaced axles. The effects of the speed and of the frequency and phase of the alternating components are analysed in detail, determining the conditions under which, in the case of forces transmitted by several axles, resonance and cancellation phenomena may occur.