The suitability of the structure above a high-speed railway bridge beam is analyzed based on the dynamics of moving railroad vehicles. To verify the accuracy of numerical simulation and to establish a practical numerical model, a theory predicting the impact of a single or multiple moving railroad cars on a simple-supported beam with damping will be developed and then implemented to analyze real case-study data. The results indicate that the vibrating acceleration induced and beam-end rotation angle need to be super-positioned with several mode shapes to obtain the approximate results. When the vehicular loading frequency approaches the bridge natural cycle, an excited resonance of the bridge occurs; the vehicle speed that causes the resonance can be accurately calculated using numerical analyses. Although the assumed conditions used in the numerical analyses may cause some analytical errors, these errors are quite limited and thus the numerical method is rather accurate for practical applications.