Field Measurement Of Human-induced Vibration And Vibration Control For Pedestrian Bridge

Pedestrian bridges have played an important role in urban transportation systems.With the development of economic and social demands,various types of pedestrian bridges continue to emerge.Under environmental load effects,pedestrian bridges,especially those with large-span flexible designs,may experience significant vibrations,which not only affects pedestrian comfort,but also poses a threat to the safety and anti-fatigue performance of the structure.The modal coupling of pedestrian bridges is severe,and the frequency distribution of vibration response is closely spaced,which can cause great difficulties in the analysis of bridge vibration signals.This paper divides the structural comfort level of two different types of pedestrian bridges based on structural responses and effectively identifies closely spaced modal parameters of the structure through multiple modal analysis methods.In addition,this paper focuses on solving key problems related to vibration reduction performance verification and optimization of tuned mass damper(TMD)in irregular-shaped pedestrian bridge projects,and has obtained reliable evaluation and optimization results.The investigate in this paper has important guiding significance for the design and improvement of pedestrian bridge structures,and provides new ideas and methods for the assessment of pedestrian bridge comfort and vibration control.The main work of this thesis is as follows:(1)The robustness of multiple modal identification methods was compared.Stochastic Subspace Identification,Eigensystem Realization Algorithm based on Natural Excitation Technique,Enhanced Frequency Domain Decomposition,Fast Bayesian FFT and Random Decrement Technique were selected.The accuracy of modal identification algorithms for structures with closely spaced modes was compared from three aspects: frequency intensity,signal length,and signal-to-noise ratio.This provides a reliable method for modal identification of structures with closely spaced modes,and ultimately provides technical support and parameter basis for the anti-vibration and anti-fatigue design and optimization of bridges.(2)A vibration reduction performance verification method was proposed for the cablestayed curved beam pedestrian bridge-TMD system.Based on the established refined finite element model and the Monte Carlo random sampling method,TMD random combination parameters(tuning frequency and damping ratio)were obtained,and the correlation between the main structural modal parameters variation and the vibration reduction effect index under the uncertainty of TMD parameters caused by environmental excitation and pedestrian load was obtained.In terms of on-site measurement,the equivalent damping ratio of the bridge was evaluated using output acceleration response signals and reliable modal analysis methods,and the measured vibration reduction range of the system was further estimated to verify the vibration reduction efficiency of TMD.(3)An optimization design method for multi-tuned mass damper(MTMD)system was proposed to improve the comfort index of pedestrian bridges and reduce induced vibration throughout the life cycle of pedestrians on the bridge.Under different comfort levels of pedestrian bridges,this paper focuses on using multi-objective genetic algorithm NSGA-II to achieve the optimization process of MTMD tuning frequency and damping ratio.Compared with traditional genetic algorithm GA and Den Hartog optimal parameter design for TMD,the obtained parameters are more adaptable to the uncertainty changes of main structural parameters,and the robustness of the bridge under human-induced vibration is improved.