SOIL STRUCTURE INTERACTION EFFECTS ON THE RESONANT RESPONSE OF RAILWAY BRIDGES UNDER HIGH-SPEED TRAFFIC

In the present contribution the dynamic behavior of beams traversed by moving loads including soil-structure interaction effects is investigated. The main application of the study is the analysis of the dynamic response of railway bridges under high-speed traffic, taking into account the interaction of the substructure with the soil when the super-structure may experience resonant conditions, and undergo considerably high levels of transverse acceleration. As this phenomenon is highly influenced by the free vibration response of the deck once the loads have left the bridge, a numerical investigation is carried out analyzing the effects of the wave propagation problem on the free vibration response of beams under moving loads. To this end a coupled three-dimensional boundary element-finite element model formulated in the time domain is used to reproduce the soil and structural behavior, respectively. A subset of bridges is defined considering span lengths ranging from 12.5 to 25 m, and fundamental frequencies covering existing deck typologies. As for the soil properties, a homogeneous half-space is considered with shear wave velocities ranging from 80 to 365 m/s. In these scenarios, the maximum response of the bridge is obtained under the circulation of a moving load in a wide range of velocities in the free vibration phase, and conclusions are derived regarding the conditions of maximum free vibration and cancellation of the response, and how these are affected by the soil properties. This information will be used in a second phase of the investigation to predict how the acceleration response at resonance is modified by the soil conditions in the case of bridges traversed by trains of loads. In this paper the approach adopted is justified, a parametric analysis is designed and preliminary results are shown.