Study On Differential Settlement And Dynamic Response For Bridge-approach

The differential settlement at bridge-subgrade transition section will reduce the running speed of the road, and also affect its comfort properties and safety directly. So it turns to be one of the key technical problems to affect the normal operation of the road. The paper analyzed the differential settlement at bridge-subgrade transition section and its dynamic response, proposed the differential settlement control criterion based on running comfort and safety, and also analyzed the dynamic response of the pavement structure at bridge-subgrade transition section. The research results can provide theoretical basis for timely maintenance and rational design of pavement of the bridge-subgrade transition section.The maximum settlement value and the maximum change value in longitudinal slope were proposed as the differential settlement control indexes at bridge-subgrade transition section, and the root mean square of the transient weighting acceleration of vibration was proposed as the comfort evaluation index. Combined with questionnaire survey and piezoelectric acceleration sensor measuring, the human comfort was evaluated when the vehicle go through a bridge-subgrade transition section from the subjective and objective way respectively. The correlation equations between the root mean square of weighting acceleration of the seat of the car and the maximum settlement value and the maximum change value in longitudinal slope at bridge-subgrade transition section were gained. Using cars as evaluation models, based on the human feeling of "somewhat uncomfortable", the differential settlement control criterion at bridge-subgrade transition section under different running speed was proposed. The vertical vibration system combined with the feeling of human, the vehicles and the road was established, and the dynamic response of 5-DOF vehicle model when going through the bridge-subgrade transition section were analyzed with the compiled MATLAB program. The models' change laws influenced by the parameters of running speed, load, setting height, the length of the approach slab, longitudinal slope change ratio, wheelbase, etc. were analyzed. The dynamic load factor was proposed as the index to evaluate the capability of the bridge-subgrade transition section to withstand the dynamic load, and the additional dynamic load and dynamic load factor when the vehicle running through the bridge-subgrade transition section were calculated. Based on the running safety of the bus, the differential settlement control criterion in bridge-subgrade transition section was put forward. In order to make a full consideration of the influence caused by the vehicles' dynamic loading and improve the pavement structural design method of the bridge-subgrade transition section, the three-dimensional finite element models for the bridge-subgrade transition section were built, and the dynamic response of the pavement with or without approach slab under the impact loading was calculated. Based on the calculation results, the dynamic load modified coefficients of the deflection on the asphalt pavement surface, the tensile stress at the base and subbase bottom, and the compressive strain on the subground surface were introduced.