The modal superposition method is an effective numerical method for solving structural dynamic response, based on modal orthogonality and the expansion theorem [14]. For large and complex structures, such as a bogie frame, the modal coordinate response of the bogie frame can be cost-effectively obtained by solving dynamics equations after its relevant modal results have been obtained. Then, through a linear transformation, the physical coordinate responses of the bogie frame can be computed. For the purpose of this study, the responses of the bogie frame are dominated by modal results at a low frequency regime as given in Table 1, which are the focus of this paper in subsequent discussions.