Experimental And Analytical Study On Serviceability Of Pedestrian-Bridge Coupled Vibration

The large-span pedestrian bridge has low damping and is easily affected by human-induced loads,and the problem of human-induced vibration serviceability is prominent.This thesis systematically studied the human-induced structural vibration and human-induced load model considering human-bridge coupling through field tests and finite element combinations.The vibration response of a very small high-span ratio（1/60）pedestrian bridge under human-induced load was studied,and the vibration characteristics of the struc-ture were clarified;based on the measured excitation load curve,the heel-drop and jumping load model was simplified.Specifically,（1）On-site in situ tests were conducted to study the vibration serviceability of a 30m span pedestrian bridge.Through the tests,the acceleration response（peak acceleration,RMS acceleration,and maximum transient vibration value（MTVV））of the pedestrian bridge under heel-drop and jumping excitation was de-termined,and the excitation load curve under heel-drop and jumping excitation were measured.The gap between the vibration responses of the pedestrian bridge structure and the wooden board was compared and analyzed in detail,and the crest factorβ_rp was introduced to facilitate the calculation of MTVV.The crest factorsβ_rp under heel-drop and jumping excitation are 0.35 and 0.29,respectively.（2）Taking the pedestrian bridge as the research object,the modal parameters（natural frequency,modal damping ratio,and modal shape）of the pedestrian bridge were obtained by simple transient excitation tests（heel-drop and jumping）and modal analysis technology.The influence of human-structure interaction on the structural damping ratio was analyzed in detail through frequency response function（FRF）.The results show that the pedestrian bridge has a low frequency（f₁=4.18Hz）and damping ratio（ξ₁=1.68～1.77%）.The vibration serviceability of the pedestrian bridge showed satisfactory results when compared with the Chinese design code,AISC design guide,and ISO standard.（3）Based on the classical beam theory,the vertical dynamic coupling control equation of the human-bridge was deduced.A finite element model of human-bridge considering human-bridge coupling was estab-lished to obtain the model’s natural frequency,modal shape,and mid-span acceleration time-domain response.The simulation results were compared with the experimental results to verify the correctness of the finite element model.Based on the model,it is found that it is reasonable to use SDOF human body model to simulate human body when considering human-bridge dynamic coupling,and the influence of human body stiffness（K）on structural response is much greater than that of human body damping（C）.The span of foot-bridge has great influence on the structural vibration characteristics and response,while the concrete mass density and elastic modulus have little influence.It is difficult to multiply the structural response when many people are excited.（4）To facilitate the evaluation of the vibration serviceability of the pedestrian bridge by engineers,a simplified heel-drop and jumping load model was proposed based on the measured heel-drop and jumping load time curve.The human-induced vibration analysis method considering human-structure coupling estab-lished in this thesis can effectively predict the vibration response of the structure under transient excitation,which provides a reference for the vibration serviceability evaluation of the very small high-span ratio pe-destrian bridge.