Simulation On Coupled 3D-Vibration Model Of Railway Bridges And Condition Assessment Of Piers And Abutment

An attempt is made to study the transverse vibration and the condition assessment of existing bridges facing to increase the axle load and speed. A coupled 3D-vibration model used to simulate the train-bridge-pier-foundation is built based on the in-situ measured data. The nonlinear elastic brick element is used to simulate the pier and soil. A non-thickness contact element is formed between the pier and the soil. It is of capability for the gap closing, opening, and sliding face to face. The bearing is simulated by a nonlinear spring-damper element; it combines the 3D beam and the pier to form the whole bridge model. To couple the train and rail, a new kind of wheel-rail dynamic contacting element is proposed. The contact elements of the base to soil, of the beam to pier, and of the wheel to rail lead to realization of the dynamic contact with the characteristic of moving mass. The in-situ measured data is used to calibrate the model for every step.After completion of the model, the free vibration of the whole bridge system is studied. It is found that the transverse frequency of the model is decreased, that is asily to cause large transverse vibration, because of the whole bridge mode. Applying train mass, the varying rule of frequency of the model with different train position is studied. The calculation method for such a with-train frequency is put forward. If the excitation frequency is near or coincident with such a frequency, the resonance or beat will be appeared. It is found that when the train mass is distributed over the whole bridge, the frequency will be kept stable.After deeply study of the characteristics of free vibration, the time-history response calculation of train and bridge is carried out. The snake movement of a train on straight rail is reappeared in the simulation. Because the amplitude of hunting wave is very small, it is unreasonable to employ that as the excitation for bridge vibration. The rail irregularity is the main excitation for bridge vibration. The dynamic response of single wheel with a spring and a damper is done, and it is agreed with the analytical one from other papers. The time-history response of a whole train running across the Dashihe Bridge is simulated later. Many influence factors are investigated in detail. Then, some important conclusions on the transverse vibration of the train under increasing axle load and speed are put forward.At last, according to the in-situ measured data and simulation, a method of condition assessment of piers and abutments with three steps is proposed. It can be used for existing bridge under the axle load of 25 tons. The examples are shown that the method is reliable.