Pedestrian-induced Vibration Analysis Of Footbridges

With increasing the modern means of transport and accelerating the traffic flow, in order to ensure the safety of the crowds and vehicles, city footbridge has been developed very quickly. Additional with increasing use of light and high-strength materials and aesthetic demand of structural appearance, newly constructed modern footbridges tend to be larger span, less mass and lower damping. In recent years several footbridges have suffered from excessive pedestrian-induced lateral vibration which severely influences the comfort of pedestrians. Based on the current summary of research results we can find that people can not understand the mechanism of lateral vibration enough. At present, more and more large span and lively footbridge have been built up in china, so it is necessary to understand the lateral vibration of footbridge mechanism and dynamic design method. In this paper, the human-induced vibration mechanism, the number of the critical pedestrian under the lateral dynamic instability, as well as the vibration reduction measures has been studied, which is based on a main span of 200m domestic cable-stayed footbridge. The main contents of the research are as follows:1. According the structural dynamics, we can simplify the interaction of people and footbridge into the generalized single degree of freedom system, and use central difference method to solve the structural dynamic response.2. This paper introduces in detail five kinds of bridge standard criterion, including the British standard BS 5400, Eurocode, ISO 10137, Swedish standard Bro 2004 and Germany standard EN03. By comprehensive compared the kinds of standards, we can find the similarities and differences of the load model and the vibration serviceability standard.3. The forced vibration theory and the self-excited vibration theory are introduced in this paper. Then the 1st bridge in huiketing of mianyang is modeled by the ANSYS commercial software, and by analyzing the dynamic characteristics of the bridge, we can gain the various order of the bridge vibration frequencies and modes. Besides, we calculate resonance acceleration response of several sensitive mode and evaluate the vibration comfort criterion, and the number of the critical pedestrian under the lateral dynamic instability is gaind by the the Newland formula and Dallard formula. Furthermore based on the central difference method and the Nakamura load model, we use matlab to analyze the 1st bridge vibration response which is simplified as the SDOF model, and study its various parameters which influence the structural vibration, for example pedestrian density, quality, degree of synchronization etc.4. Several vibration reduction measures to improve the footbridge vibration and three kinds of commonly used damping system are also present in this paper, including tuned mass damper (TMD), tuned liquid damper (TLD) and viscous damper. Then according to the simulation results of the 1st bridge, we put forward a TMD damping design to meet the need of the vibration comfort requirements.