| In order to improve residents’ sense of happiness and gain,many cities begin to build greenway systems.In the greenway system,a large number of landscape footbridges have been built.In order to pursue light and beautiful structural forms,these footbridges show the characteristics of low frequency,which makes the structural frequency close to or fall within the walking frequency band.In some cases,the resonance response is generated due to pedestrian walking excitation,resulting in the discomfort of pedestrians on the bridge.At present,there is no perfect regulation on the comfort analysis and vibration reduction design of footbridges in China,and there is little research on the comfort analysis and vibration reduction design of footbridges with complex structure and strong nonlinearity.Based on a typical long-span cable-stayed footbridge,this thesis analyzed the comfort of human-induced vibration,and used Tuned Mass Damper(TMD)to reduce the modal frequency that did not meet the comfort requirements.Aiming at the problems existing in the classical design method of TMD,a genetic algorithm was proposed to optimize the parameters of TMD,and the advantages of this optimization method were comprehensively evaluated.The main contents and conclusions of this thesis are as follows:(1)This thesis discussed the research status of domestic and foreign researchers on pedestrian walking load,footbridge comfort index and TMD damping parameter optimization,and expounded the significance of pedestrian-induced vibration comfort analysis and damping optimization of footbridge.(2)The finite element model of typical cable-stayed footbridge was established by using the finite element software ABAQUS,and the modal calculation was carried out.The finite element model was checked by the bridge modal measurement.The modal analysis showed that the bridge is a low-frequency and dense frequency structure,and there are multi-order modal frequencies within the walking sensitive frequency band.(3)The walking load excitation was applied in the finite element model,and the step frequency is the same as the sensitive frequency of the bridge.The acceleration time history response of the main beam was calculated.The comfort of the bridge was evaluated by using the comfort index in the ‘Design of Footbridge: guideline-EN03’ and the International Standardization Organization 10137.In contrast,using the evaluation index in the ‘Design of Footbridge: guideline-EN03’ to evaluate the comfort of the bridge is more comprehensive and strict.(4)The damping principle of TMD was systematically discussed,and the damping effect of TMD with different mass ratio was analyzed in the finite element model.The results showed that the damping effect is better with the increase of TMD mass ratio.However,when the mass ratio is less than 0.01,the damping effect of TMD increases greatly with the increase of TMD mass ratio.When the mass ratio is greater than 0.01,the damping effect increases slowly and uneconomically with the increase of TMD mass ratio.Therefore,it is necessary to reasonably determine the mass ratio of TMD in engineering design.(5)According to the finite element calculation results,the TMD parameters were determined,and the field test was carried out.The acceleration responses of the bridge under different pedestrian excitation conditions when TMD is closed and opened were collected.The test results showed that TMD can effectively control the vibration response.The vibration reduction rate of TMD was calculated.Compared with the finite element calculation results,it showed that the finite element modeling method can better calculate the vibration reduction effect of TMD.(6)Based on genetic algorithm,the TMD parameters of ABAQUS full bridge finite element model were optimized,and the damping effect was compared with that of classical TMD design method.The results showed that this method can control the vibration response under various frequency loads,and further improve the damping performance of TMD. |
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