Research On Vibration Damping Analysis Of Large Cantilever Footbridge Under Load Excitation

The reform and opening-up has made China's economy develop rapidly,the infrastructure is further perfected,and the spiritual needs of the people are no longer limited to the traditional concrete structure.High-strength materials and beautiful shape of the structure in the application of engineering,modern bridge is characterized by large-span,soft,irregular,low damping.The overhanging footbridge has been favored by designers for its graceful linear and powerful visual impact.However,in recent years,some pedestrian bridges have been caused by walking loads of large vibration,vibration and speed of more than the comfort range to cause pedestrians to walk uncomfortable or even cause bridge fatigue damage.At home and abroad,scholars have done a lot of researches on human vibration,and the vibration reduction analysis is mainly focused on simple supported beam,continuous beam and frame,so it is very rare to analyze the vibration of large cantilever special-shaped bridge.For the conventional structure with obvious vibration type,the vibration damping design can be considered only by taking the quality of a certain order mode,if the coupling effect of the structure is obvious,the influence of multimode is to be considered.Otherwise,there will be a great difference between the existing analysis and the actual structure.Therefore,this paper studies the human-induced load characteristics,vibration-reducing excitation and vibration-damping analysis of cable-stayed bridge,and the results are as follows:(1)Taking a large cantilever pedestrian bridge as the engineering background,the general dynamic analysis process is introduced,and the influence of damping ratio on the natural vibration characteristics is analyzed.The software ANSYS is used to establish the finite element model of dynamic analysis.The influence of the parameters of steel tube section,cable section,structure and other parameters on the dynamic characteristics is studied.The structural stiffness can be significantly enhanced by forming a ‘closed steel box beam' in the upper and lower part of the main beam.But at this time,the vibration frequency is still less than 3Hz,so other control standards need to be sought.(3)As for pedestrian bridge,harmonic response analysis is used to determine the continuous dynamic performance of bridges.A centralized force is applied to simulate the effect of mobile live load,and the effects of speed and other parameters are analyzed.Crowd load model is applied to transient dynamic analysis.Considering the vertical acceleration response value under non synchronous frequency,it is suggested that the maximum vibration effect is when the step frequency is 2.5Hz.(4)According to different standards,we classify the shock absorber,and analyze the structure without damping for the main structure,and the sub structure is damped and undamped.The range of damping frequency increases slightly,but the increase is not obvious.Therefore,by increasing the quality of sub structure,the effective damping effect can not be achieved.The vibration damping analysis of large cantilever pedestrian bridge is carried out.The effect of TMD and MTMD vibration damping is compared.The results show that the working frequency of MTMD is larger and the effect of vibration damping is better.