Vibration And Vibration Control Research For Large-span And Light Footbridge

With the development of footbridge structure, the human-induced vibration has become one of major problems affecting the use performance of footbridge. In regard of the vibration problems arising from more and more large-span light footbridges, in this paper, walking load, human-induced bridge vibration mechanism, vibration comfortability assessment, and footbridge vibration control by TMD has been investigated deeply. The major research results are as follows:(1) Vibration control mechanism of the structure by the MTMD was investigated and the motion equation of MTMD -structure system has been established. Forthermore, the effects of the MTMD frequency range(Δγ), MTMD damping, MTMD number, generalized mass ratio, frequency variation of the master system, excitation time, and band breadth of white Gaussian noise on the vibration control were discussed. Finally, the rational parameters for the MTMD were recommended.(2) Development of research on walking load has been reviewed, and the excitation load for single-person and crowd by the scholars of various countries has been compared. Based on these, the effects of bridge vibration on the pedestrian comfortability were discussed. The result shows that the overseas research on footbridge vibration mainly concern comfortability, which focuses on vibration acceleration of footbridge. But in China, because relative less research has been carried on the footbridge, only the free vibration frequency of footbridge was concerned.(3) The calculating theory for footbridge vibration has been discussed and the calculation formulas specified by various countries have been introduced. Fourthermore, the motion equations for single-person and crowd crossing the bridge have been established and the forced vibration analysis method was applied to seek the solution in time domain.(4) In this paper, the Qingdao Guangrao Road Footbridge was takes as an example, and the vibration performance when single person, a group of people or crowd crossing the bridge has been investigated. The results show that when fp/f approaches 1, the resonance occurs, the displacement and acceleration at the mid-span reach the maximum value.When a group of people or crowd crosses the bridge, even though with the increase of pedestrians the vibration of bridge will be intensified. However, because the steps are random, the vibration will not be intensified in the proportion with pedestrian number. If the stiffness of the bridge beam and the free-vibration frequency has been increased, the resonant speed caused by pedestrian walking load to bridge will accordingly be raisen. Because the footbridge span is very large, its free vibration frequency can not meet domestic regulations, and its acceleration will not meet the limit value specified by overseas regulations. Therefore, the footbridge will cause large vibration in use.(5) In this paper, the dynamic equation of the TMD-bridge-pedestrian system is established and the control vibration effect of MTMD for Qingdao Guangrao Road Footbridge is investigated. The analysis results show that the adoption of 12 TMDs to control footbridge vibration is an effective method, whatever it is a single person, a group of people or crowd, the effect of the vibration control of MTMD is very remarkable. Even though the adoption of MTMD can not improve the free vibration frequency of structure, after the adoption of MTMD, the maximum vibration acceleration of footbridge will not exceed 0.35m/s2, which meet the requirements of vibration limit value specified by overseas regulations.