Research On Bridge Vibration And Acoustic Radiation Under Stochastic Excitation

Nowadays, China is undergoing the process rapid urbanization. With the increase of population density, there has been great increase in traffic density which in turn caused troubles such as structural vibration and noise problem. This thesis is focused on the vibration serviceability problem and low frequency noise radiated from bridge vibration. In order to consider the uncertainty of excitation and human vibration sense a probability-based approach is proposed. The stochastic pedestrian load and stochastic traffic flow were simulated by simultaneously considering the effect of several random factors and the probability distributions of bridge vibration under stochastic loads were then investigated. Additionally, according to the existing test result or standard a probability-based evaluation method is proposed considering the individual difference between pedestrians. Therefore, the vibration serviceability and noise can be evaluated objectively and comprehensively.Bridges with different forms were considered for investigation, and the main contents of this study include:1. A vibration calculation method with accurate simulation of footfall force is present in this thesis. The accuracy of proposed method was verified by comparison with field test. The probability distribution of bridge vibration under stochastic pedestrian load was studied theoretically considering its randomness. Based on the serviceability analysis, structural vibration induced uncomfortable may occur even when the fundamental frequency of the footbridge is higher than3Hz.2. The vibration analysis and serviceability evaluation of suspension footbridge was adopted for study. A simple nonlinear vibration calculation method based on cable theory was proposed. The accuracy of proposed method was verified by comparison with field test. The results show that the fundamental frequency of suspension footbridge is very low. Step load is prone to resonate with higher order modes of the bridge in vertical direction, which may cause uncomfortable feelings.3. A below-hanging footbridge is adopted for study. The vibration characteristics and serviceability evaluation under stochastic human and vehicle excitation are investigated. Especially the impact action from vehicles when passing expansion joint is included for investigation. The simulation method and effect of impact action from expansion joint is investigated. The result shows that impact effect is the main reason for causing uncomfortable feelings in this type of footbridge. 4. The calculation method and evaluation of low-frequency noise radiated from bridge vibration of a separated steel box girder bridge were investigated. The low frequency noise was calculated from bridge traffic vibration based on the summation of point sources. Then the character of low-frequency noise radiated from the bridge vibration under random traffic load is analyzed. Based on annoyance method, G-weighted SPL and C-weighted SPL were used as evaluating indicators of infrasound and low-frequency noise respectively for noise evaluation. The result shows that the low-frequency noise mainly comes from the local vibration of bridge deck in the frequency range of10-20Hz. The infrasound and low-frequency noise can be alleviated by reducing the road roughness or by increasing the bridge deck stiffness.