In this paper dynamic analysis of multi-span bridges subjected to a moving vehicle is investigated. Finite element method is used to model the problem, and the Newmark technique is used for direct integration of the governing equations. In this regard, the moving node technique is applied to represent the dynamic responses of the multi-span bridge, and the vehicle is idealized as a sprung-mass system. Results indicate that the maximum vertical deflection of the multi-span bridge occurs at the span under the vehicle. It was found that the mid-span vertical deflection of spans for dynamic and static loading are not the same, and the position of the vehicle for maximum deflection for dynamic and static loading are also different, and the distance between two maxima increases by the velocity of the vehicle. Considering the results obtained from axial dynamic responses of the mid-spans, it is interesting to note that by increasing the velocity and acceleration or deceleration of the moving vehicle the vibration amplitudes of the axial responses increase. It is also worthy of noting that by increasing the velocity or acceleration of the moving vehicle, the vibration frequency of the axial responses decreases during the constant-speed period.
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