Evaluating vertical conditions of bridge substructures of heavy-haul railway lines based on dynamic stiffness and pier vibration response

摘要

When it is necessary to increase the freight volume, the related increase in the train axle loads can potentially affect the bearing capacity of bridge substructures. Therefore, the structural integrity of bridge substructures should be evaluated, and their capacities need to be estimated. Existing studies have only investigated the lateral health condition of piers and foundations of bridges. To evaluate the vertical condition of bridge substructures, in this study, a dynamic transient response method (TRM) was developed using newly designed equipment. The vertical dynamic stiffness of a bridge foundation was employed as the main evaluation index. Subsequently, in situ experiments were performed on 62 bridge foundations of a heavy-haul railway line, including three types of foundations. Train-induced vertical and lateral vibration responses on the pier tops were also measured. The relationship between the vertical dynamic stiffness of the foundations and the train-induced vibration amplitudes on the pier tops was analysed. Subsequently, the support vector machine (SVM) method was employed to predict the dynamic stiffness of the bridge foundations when the TRM test could not be performed and the train-induced vertical vibration response on pier tops could be tested. Finally, a three-step evaluation strategy was proposed to comprehensively assess the vertical conditions of bridge substructures using the above methods. The study indicates the following: (1) The redundancy of the vertical bearing capacity is completely different from that of the horizontal vibration amplitude. There may be a certain error in the evaluation of a pier foundation when only the horizontal vibration amplitude is used to analyse its health condition. (2) The dynamic stiffness obtained by the TRM can effectively reflect the vertical condition of a bridge substructure and can be employed as an index in the detailed evaluation stage. (3) Using SVM, the dynamic stiffness of a foundation can be predicted with the measured amplitudes of the train-induced vertical vibration on the pier tops. The amplitudes of train-induced vibration and SVM-based prediction of dynamic stiffness can be used as early warning indicators in the scoping evaluation stage.