Study Of Vehicle-road-bridge Vibration Caused By The Road And Bridge Unevenness At The End Of The Bridge

The differential settlement between the bridge and approach embankment and damaged expansion joint are both parts of the road/bridge unevenness at the end of the bridge, which can aggravate the vibration of passing vehicles, cause rider discomfort, magnify the impact on the bridge, and accelerate the deterioration of the bridge deck, expansion joint and other components, forming a vicious cycle. Studies have shown that the impact loads applied to the deck slab at the end of the bridge may be 5-6 times as large as the static loads, and the impact effect considered while designing the deck slab should be based on the responses at the cross section that is close to the damaged expansion joint. Therefore, there is a need to study the local impact effect on the deck slab near the end of the bridge caused by the road/bridge unevenness near the end of the bridge, wh ile few studies focusing on such issues have been reported. In the bridge design codes, the impact factor was introduced to evaluate the local impact on the deck slab, which was derived from the global response, such as the midspan deflection. However, it may not be appropriate to apply such impact factors to the bridge deck slabs whose controlling internal force is usually the transverse bending moment.In addition, no design guidance for the allowable differential settlement is yet available, both in China and abroad. Many researchers have suggested the allowable differential settlements based on the ride comfort investigation, while a more comprehensive study, considering the vehicle users comfort, running safety and the impact on the bridge, for the allowable differential settlements is still not available.Thus, in this study, a vehicle-road-bridge system model is developed firstly. On this basis, the effect of the expansion joint condition on the local impact factor, which is calculated from the transve rse bending moment of the bridge deck, and the global impact factor, which is calculated from the global dynamic response is then investigated. Results show that the damaged expansion joint can magnif y the local impact factors significantly while the effect on the global impact factor is limited.In addition, the effects of the differential settlement on the vibration of the vehicle users, vehicle and bridge, which are evaluated based on the users' comfort, vehicle running safety and the impact on the bridge, including the local impact factor for the bridge deck slab and the global impact factor respectively, are also studied. Finally, allowable differential settlements are proposed based on the recommended limits on the three indexes in relevant codes.