Studies On Vibration Response Of Highway Bridge Under Multi-row Vehicle Loads

At present,the traffic flow of highway bridges is increasing,and the form of traffic flow is increasingly complex.Compared with the impact effect of a single vehicle on the bridge,the bridge structure under multi-vehicle loads will generate a greater vibration response,affecting the driving comfort and the service life of the bridge.In the past,most of the research on the vehicle-bridge coupled vibration is to analyze the vibration response of bridges under the condition of a single vehicle or longitudinal multi-vehicle in a single lane,and few studies have involved vibration response of bridges under horizontal multi-vehicle condition in different lanes.Vehicles in different lanes not only have direct coupled vibrations with the bridges,but also have indirect coupled vibrations with the other vehicles.Therefore,it is necessary to study the vibration response of bridges under the condition of horizontal multi-row vehicles which is closer to actual working conditions.In this thesis,we established the vibration equation of multi-vehicle system based on D’Alembert principle,and we established the vibration equation of bridge by using modal analysis method.The vibration equation of vehicle-bridge coupling system was established by means of displacement compatibility condition and force balance condition.We used the harmonic superposition method to simulate the road irregularity.The vehicle-bridge solving coupling program based on Newmark-beta integral method was compiled by MATLAB,and ANSYS modeling and modal analysis were carried out for a simply supported beam bridge and a continuous beam bridge.Then,we studied the variation of vertical displacement response and impact coefficient of bridge structure with the change of vehicle speed,vehicle spacing and road roughness under three non-unbalanced working conditions: single-vehicle,horizontal two-vehicle and longitudinal two-vehicle conditions.What’s more,we studied the vibration response of the bridge under unbalanced vehicle loads.The results show that the midspan displacement response and impact coefficient of the bridge do not increase monotonously with the increase of vehicle speed under the three non-unbalanced working conditions,and the change of impact coefficient with vehicle speed under the conditions of single-vehicle and horizontal two-vehicle conditions are similar,but the impact coefficient curves of the longitudinal two-vehicle condition fluctuate around the impact coefficient curves of the single-vehicle condition.The maximum dynamic displacement and static displacement of the midspan decrease with the increase of vehicle spacing,and the impact coefficient increases with the increase of vehicle spacing under the horizontal two-vehicle condition.The maximum dynamic displacement and the maximum static displacement of the midspan decrease with the increase of vehicle spacing under the longitudinal two-vehicle condition,and eventually tend to a fixed value.The impact coefficient of longitudinal two-vehicle condition will fluctuate around the impact coefficient under the condition of single-vehicle,and finally it will be fixed.With the deterioration of road conditions,the displacement response and impact coefficient of the three non-unbalanced working conditions gradually increase,and the change of impact coefficient under single-vehicle and horizontal two-vehicle conditions are similar.With the increase of vehicle speed,the impact coefficients under unbalanced single and unbalanced horizontal two-vehicle conditions are similar,and the impact coefficient under unbalanced longitudinal two-vehicle condition fluctuate around them.However,compared with the results under non-unbalanced vehicle load,the impact coefficients will increase due to unbalanced vehicle load.