Test And Evaluation Of Human-induced Vibration Serviceability Of Large-span Pedestrian Bridges

Large-span pedestrian bridge structure adopts tree-shaped steel pipe concrete piers and steel box girders with beautiful shapes and reasonable force,and the appearance of its tree-shaped piers can integrate the building and the surrounding natural environment,which is in line with the mentality of modern people who want to return to nature and enter nature.With the construction trend of large span and light weight of pedestrian bridge structures,the problem of human-induced vibration has gradually become one of the important problems affecting the use of pedestrian bridges.However,relatively little research has been done in China on the vibration characteristics and acceleration response of large span pedestrian bridges.In this paper,the vibration comfort of a large-span pedestrian bridge is systematically evaluated by means of bridge comfort tests under pedestrian walking and footfall excitation,parametric analysis of finite element models,and theoretical calculation methods,using the Runmin River large-span pedestrian bridge in Kuitun as the engineering background.The main contents of this paper are as follows.(1)Compare the comfort evaluation indexes and evaluation thresholds of the existing pedestrian bridge design codes at home and abroad.The vibration comfort performance of a 30 m span pedestrian bridge was studied through field tests.The tests mainly focused on the vibration characteristics and acceleration response of the pedestrian bridge under environmental,footfall excitation,and walking excitation loads.The largespan pedestrian bridge tested had a first-order vertical frequency of 3.35 Hz,a damping ratio of 0.018,and a first-order vertical vibration pattern of mainly bending.It meets the requirements in the Technical Specifications for Urban Pedestrian Bridges and Pedestrian Walkways.The vibration acceleration response under human-induced load should be considered.(2)Establish a refined finite element model of the large-span pedestrian bridge,and suggestions were made on cell selection,cell mesh size,intrinsic model,and damping ratio parameter values.The vibration characteristics and acceleration response results of the model are in good agreement with the experimental results,which verifies the accuracy of the fitted drop-foot simplified model.Meanwhile,the vibration characteristics and acceleration response of the pedestrian bridge with a large span were carried out in terms of height-to-span ratios(1/20,1/40,1/50,1/60,and 1/80),common concrete paving thicknesses(0mm,50 mm,100mm,150 mm,and 200mm),concrete fill height of tree columns(five different concrete fill ranges)parameters on the response.(3)A theoretical calculation method applicable to the self-oscillation frequency of pedestrian bridge was derived and verified by the test results.The calculation method of the peak acceleration response of the pedestrian bridge was derived and solved based on the vibration type decomposition method.The results were compared with the test and finite element calculation to confirm the applicability of the formula.(4)The perceptual limits for vibration comfort evaluation were compiled,and reasonable evaluation thresholds for vibration comfort of large-span pedestrian bridges were suggested by collecting data on personnel’s perceived response to vibration through tests of pedestrian-induced load excitation(heel drop and walking)on pedestrian bridges,corresponding to the acceleration response values,the proposed thresholds were established.