This study investigates the dynamic response of a railway bridge under train passage. Three load models designed around the Swedish Steel Arrow freight train are tested and compared. A series of Concentrated Forces, a succession of single degree of freedom Sprung-Masses, and a sequence of complex multi-degree of freedom Train Wagons.
The increase in accuracy of the representation corresponds to taking into account the inertial properties of the wagons. The track-bed layer is substitute by a sequence of regularly spaced couple of springs and dampers at the sleeper distance.
Under the assumption of this work, a portion of the ballast vibrates with the sleeper during train passage. Both bridge and rail are modelled under Bernoulli-Euler beam theory. The dynamic behavior of the bridge is investigated in presence or absence of vertical track irregularities. The main conclusions of the report can be summarized as:
• The dynamic amplification attains its maximum value, for every train model, at the critical train speeds of 120 km/h. Proper resonance has also been detected at the speed of 60 km/h in all the simulations;
• The Concentrated Forces model provided an upper boundary of the acceleration response of the bridge while the Sprung-Mass systems a lower boundary. The response of the two models is in very good agreement at non resonance speeds. The simulation with Train Wagons loading does not fit completely this trend, it adds two peaks on the diagram; Besides that, the bridge response lies between the two limits;
• The presence of track irregularities determines a variation of the bridge dynamics only if combined with Train Wagon load model. The Concentrated Force pattern couldn’t detect the modification of the profile while the Sprung-Masses case provided a diagram of maximum acceleration similar to the one over flat rail simply shifted upwards;
• The position of the track irregularities along the bridge influence its dynamics.
Author: Martino, Davide