Study On Human-induced Vibration Response Analysis And Vibration Reduction Control Of Long-span Special-shaped Pedestrian Arch Bridge

With the development of society and cities,pedestrian bridges are widely used to alleviate urban traffic pressure and ensure pedestrian safety.Nowadays,pedestrian bridges must not only meet the requirements of usage,but also meet the aesthetic requirements.Therefore,there gradually emerges large-span,soft and novel pedestrian bridge structures.However,it often leads to a low fundamental frequency and low damping of the pedestrian bridges,and it may easy result in the fundamental frequency of the pedestrian bridge to coincide with the walking frequency of people,which emrges the resonance phenomenon between people and bridge.This paper is based on a large-span special-shaped pedestrian arch bridge in Guangdong Province.Firstly,using ANSYS and Midas to establish the finite element model,and using static and dynamic forces to analyze the rationality and accuracy of the model.Secondly,based on the data collected by the field modal test to study modal parameter identification,the modal parameters are identified by EFDD and NExT/ERA.We use frequency domain EFDD and time domain NExT/ERA to identify the modal parameters.And we will compare the identification results with the results of the DHDAS?dynamic signal acquisition and analysis system?.Thirdly,the finite element model is modified by the identified frequency,and the comparative analysis is carried out by using first-order algorithm of ANSYS and genetic algorithm of MATLAB to ensure the accuracy and reliability of the correction results.Fourthly,based on the modified finite element model to analyze the human-induced vibration response.And we use four standards from abroad to analyze the comfort of this special-shaped pedestrian arch bridge.Finally,in the case that the comfort degree of the crowd load model does not satisfy the threshold of the IS0 specification,we will use two vibration reduction schemes,STMD and MTMD to analyze the effect of vibration reduction.The main research work and conclusions of this paper are as follows:1.We use finite element software,ANSYS and Midas to analyze the special-shaped pedestrian arch bridge by static analysis and dynamic analysis.Under the eternal load and live load,the maximum displacement errors obtained by ANSYS and Midas are 4.35%and 5.55%respectively.When performing modal analysis,the maximum error of the natural vibration frequency of the special-shaped pedestrian arch bridge from these two softwares is 2.36%.The analysis results show the rationality of modeling with ANSYS and can carry out the next research work.2.Modal parameter identification is performed by using EFDD and NExT/ERA,respectively,and compared with the identification results of Op.polylscf,which is contained in DHDAS.The frequencies identified by the three identification methods are in good agreement,which the maximum error between the frequencies identified by Op.polylscf and the theoretical frequencies is 16.25%(arch rib transverse 3^rd).But the damping ratios identified by the three methods are quite different.Considering comprehensively,the result identified by EFDD is finally selected as the measured value in the finite element model correction.3.Based on the measured frequency values,the first-order algorithm of ANSYS and the genetic algorithm of MATLAB are used to modify the finite element model.Both algorithms can effectively perform global modification.The frequency error obtained by the first-order algorithm modification is within±5%.However,for genetic algorithm,the frequency error of each mode is less than that of the first mode,except that the third-mode frequency error is-5.65%.The mutation rate of the modified parameters obtained by both two algorithms is±15%.Although the first-order algorithm has high precision and low time consumption,it needs to set a reasonable convergence tolerance of the objective function to avoid falling into local optimum.Therefore,it is recommended to use a genetic algorithm with better overall to ensure the reliability of the results.4.According to the modal,we identified frequency,the natural vibration frequency of the special-shaped pedestrian arch bridge is found to be within the walking frequency band?1.6-3.2Hz?,which is prone to resonance phenomenon between people and bridge.Therefore,the human-induced vibration response analysis is carried out by using specification set by Britain,Sweden,Germany and IS0,and acceleration is adopted to evaluate the comfort degree of the special-shaped pedestrian arch bridge.The analysis results show that the response acceleration of the special-shaped pedestrian arch bridge under the crowd load model of the IS0 is higher than the threshold,and further vibration reduction control treatment is needed.5.Aiming at the problem of acceleration over limit of this type of pedestrian arch bridge under crowd load mode in international standard organization,STMD and MTMD are used to compare and analyze the vibration reduction effect of different loading methods.The analysis results show that both STMD and MTMD can achieve vibration reduction greatly,and different loading methods have different effects.The vibration reduction effect of MTM is superior to STMD,and it has stronger robustness.Moreover,the quality of a single TMD in MTMD is small,making it easy to manufacture,transport and install.Therefore,it is recommended to use MTMD for vibration reduction control.