Research On Vibration And Vibration Isolation Measures For Footbridges Induced By Road Vehicle Loads

With the dramatic increase in urban population and urban traffic together with ever-widening roads, the footbridges are widely used in vehicular and pedestrian intensive areas of the city and the main roads in order to ensure the smooth flow of traffic and pedestrian safety. With the application of high-strength and lightweight materials, innovative structural systems, new construction techniques and modern structural analysis methods, the footbridges are developing towards to the light, large span, delicate and exquisite direction. For the large-span and light footbridge, the natural frequency is lower, so the footbridge will occur substantial vibration due to excitations such as pedestrians on the bridge and vehicle loads under the bridge. In domestic, the design of footbridges always ignores the influence of vehicle loading. In the severe effect of the traffic during peak periods or large buses, flat trailers, concrete mixers and dump earth-moving cars and other vehicles, the dynamic effect of the vehicle incentive can not be ignored. This incentive is unlikely to damage the structures, but it often brings discomfort even nervous and panic emotion to pedestrians on the bridges. In a word, few studies are under research for footbridge vibration generated by passing vehicles below. Therefore, it is necessary to study the dynamic response of footbridges due to road traffic loading and evaluate the vibration serviceability of the footbridges then put forward reasonable and feasible vibration control measures.According to the tests of representative footbridges in Wuhan, this paper takes the footbridge whose vertical natural frequency is lower than3Hz as engineering background, and researches on vibration and vibration isolation measures for footbridges induced by road vehicle loads. The main research contents are as followed:(1) This paper collects and summarizes the vibration serviceability specifications in domestic and abroad and compares the application scope, evaluation values and methods, then proposes the assessment criteria of vibration serviceability for footbridges. According to the survey of footbridges in Wuhan, the field measurment of natural frequency is conducted on six newly-built footbridges and the first footbridge of Wuhan University of Technology which owns more complaint. This paper chooses the first bridge of Wuhan University of Technology whose vertical natural frequency is lower and the magnitude of traffic flow is larger and studies the evaluation of vibration serviceability and vibration control of footbridges.(2) The major theory research results of ground vibration induced by road traffic loading at home and abroad including vibration characteristics and its propogation discipline is introduced. It provides references to dynamic analysis by brief introduction of common analysis methods of vehicle vibration.(3) The first footbridge of Wuhan University of Technology is simulated by finite element software and modal analysis and dynamic response due to vehicle loads is conducted. Vibration serviceability of footbridges induced by vehicle loads is evaluated.(4) Aiming to the problem of vibration serviceability of footbridges, the new-type of vibration isolation module proposed by our research team is studied by experiment. The effect of vibration reduction of the new type vibration isolation module is evaluated.(5) Based on the vibration theory of wave of any circle layer radia inhomogeneous isolation material, the surrounding soil vibration of vibration isolation module is simulated by three dimensional finite element through finite element software. The model analysis results are compared with experiment results, and the effect of vibration reduction is evaluated.(6) The new type vibration isolation module is applied in the first footbridge of Wuhan University of Technology. The dynamic response of the footbridge with the vibration isolation module is analyzed, and the vibration serviceability is assessed.