Human-induced Vibration Analysis Andcomfort Assessment Of Long-spanflexible Suspension Bridge

In recent years,more and more investment has been made in the construction of tourist scenic spots,more and more scenic spots have been constructed,and the number of scenic footbridges built in various scenic spots has also increased.With the rapid progress of high-strength flexible materials,the continuous development of structural system calculation methods,and the continuous breakthroughs in construction and manufacturing technology,the number of "large span" and "soft" suspension bridges has increased.And because of its unique shape,the suspension bridge has both modern technological sense and aesthetic beauty,which makes more and more scenic spots build glass landscape suspension bridges.This paper analyzes the effects of different structural parameters on the natural vibration characteristics of pedestrian bridges,considers the effects of different pedestrian movement modes and movement frequencies,and analyzes the human-induced vibration of flexible landscape suspension bridges that rely on the project.Evaluation method of comfort level,and this method was used to evaluate comfort level.(1)Based on the engineering background and technical indicators of the bridge,a bridge model was established,the principle of calculating the structure’s natural vibration characteristics was introduced,the influence of damping ratio on frequency and period was analyzed,and a flexible suspension bridge structure with small damping ratio was obtained,Ignore that the damping has little effect on the results of the modal analysis.The influence of structural parameters such as changing the size of the original structure stiffening beam and the main cable and installing flat links on the dynamic characteristics of the structure is analyzed.It was found that installing a flat link on the bottom of the stiffening beam can increase the fundamental frequency,and make the stiffening beam a more closed box-like structure,which significantly improves the torsion resistance of the stiffening beam.Therefore,it was selected to install a flat link on the bottom of the stiffening beam for structural optimization.The modal frequency of the optimized structure still cannot meet the requirements of domestic codes,and other methods need to be found to evaluate the vibration comfort of the bridge.(2)Comparing the evaluation requirements for comfort in domestic and foreign codes,it is found that the provisions of China’s codes on the comfort of pedestrian bridges are not perfect,and no solution is given when the natural frequency of the structure cannot meet the requirements of the code,which leads to The specifications cannot meet the actual construction needs of the project.When the frequency of the engineering structure cannot meet the requirements of the specification,the vibration acceleration can be used to evaluate the comfort of the engineering structure.(3)According to the step frequency characteristics of pedestrian load itself,the pedestrian movement state is simulated by uniformly distributed and mobile loading,and the human-induced vibration analysis of the long-span flexible suspension bridge is carried out using the corresponding crowd load and small group pedestrian load.It is found that the strength of the dynamic load contributed by the total number of people on the bridge has an approximately linear relationship with the strength of the vertical and lateral vibrations of the bridge.It is concluded that when the step frequency is 2Hz,the acceleration response is the largest,and this frequency can be used as the vibration damping control frequency.The modal frequency of the bridge is densely distributed within the pedestrian load step frequency distribution range.After calculation and analysis,the bridge is prone to resonate with pedestrians with a walking frequency of about 2 Hz.(4)Collect and compare multiple walking load models at home and abroad for comparison and analysis.It is concluded that the vertical walking force model in foreign codes removes the influence of the self-weight part and considers only the dynamic load part.The model proposed by the author considers the influence of self-weight.When the researcher model removes self-weight,the change law of the load model is basically consistent with the change law of the norm model.A method of comfort assessment using the latest load model established by Dr.Chen Jun in combination with EU regulations is proposed,and this method is used to assess the comfort of a large-span flexible suspension bridge.Vibration comfort.(5)Select the most unfavorable motion state to carry out uniform loading.The maximum response acceleration generated is much smaller than the maximum response acceleration generated by concentrated loading according to the total excitation force of the same magnitude.From this,it can be concluded that the number of people who synchronize the number of people on the bridge and the distribution of the number of people who synchronize on the bridge have the greatest influence on comfort.(6)In order to control the use comfort of the project bridge,different measures are used to control the comfort in the use phase and the design phase.Use the stage to control the total number of tourists on the bridge,and set up warning signs to remind tourists not to gather and walk together.In the design stage,a shock absorber was installed for vibration analysis.TMD was installed on the suspension bridge for vibration analysis.The time-history analysis results showed that the acceleration response of the pedestrian suspension bridge for this project after installation of TMD was greatly reduced,and vibration after the installation of the shock absorber Comfort meets the requirements.