A Study On Human-induced Vibration Comfort Of Footbridges

With the emergence of a large number of new materials and complex structural forms,pedestrian bridges exhibit the characteristics of large span,low damping and light weight,which are susceptible to significant vibration caused by human-induced loads and affect the safety of pedestrians on the bridge.In most existing codes,the representative value of the structure is used as an indirect criterion for evaluating pedestrian vibration comfort,but there is no clear definition of the perceived level of vibration comfort of pedestrians.In addition,most researchers use the peak acceleration of the structure under resonance to compare with the acceleration limits required by the code,and assess the comfort level in a "one-size-fits-all" manner based on a single determined value,ignoring the randomness of pedestrian loads.There is no study on the comfort of pedestrians considering the real vibration response and subjective uncertainty.This paper addresses the above problems by analyzing the real vibration response of pedestrians considering randomness,the quantitative calculation method of humaninduced vibration comfort,the improved comfort evaluation method and the simplified calculation of structural vibration response.The main contents of this research include:(1)Four walking models considering time-space multi-scale are established to describe the randomness in the human-induced vibration problem,and the vertical vibration response analysis method considering pedestrian real sensing is proposed.The concept of "synchronous response" is defined,and the difference of peak response moments in different areas of the pedestrian bridge is analyzed.By studying the correlation between the real maximum vibration response of pedestrians and the peak acceleration in the span of the structure,the vibration response discount factor is defined and an approximate calculation method for the real maximum vibration response of pedestrians is established.The accuracy of the approximate calculation method is verified by comparing the calculated values with the actual values.(2)The nonlinear relationship between the subjective response affiliation value of pedestrians under vibration response and the vibration response of pedestrian bridge structure is studied,and an improved affiliation function is proposed.Based on the improved annoyance rate calculation model,an approximate pedestrian bridge annoyance rate curve with the accuracy meeting the engineering application requirements is given,and the error between the calculated curve and the approximate curve did not exceed 0.03.The comfort evaluation method is improved based on the vibration time range of the actual pedestrian perception,and a pedestrian bridge vibration comfort evaluation method considering the actual pedestrian perception and the improved annoyance rate model is proposed,and a vibration comfort study is conducted for the pedestrian bridge in Huatai,Jingzhou.The results show that the calculated value of annoyance rate considering pedestrian’s real feeling is closer to the measured value.(3)In order to quantitatively analyze the vibration comfort of pedestrian bridges with different crowd densities,the results are evaluated in the form of probabilities.Firstly,a random walking load considering individual variability is established to derive the analytical solution expression for the vibration response of a pedestrian bridge with multiple people crossing the bridge and a simplified formula for the vibration response in the resonance case,and the analytical solution proposed in this paper is compared with the numerical solution and experimental values.Secondly,the acceleration response of simply supported beams in different human density cases is calculated by using the analytical solution method,and the distribution law and cumulative probability of the peak acceleration response are analyzed.The cumulative probability of exceeding the acceleration limit is proposed as the comfort evaluation index,and the Monte Carlo random sampling method is used to verify the evaluation method proposed in this paper.The results show that the analytical solution method can efficiently calculate the dynamic response of the pedestrian bridge structure and can also be used for structural vibration comfort estimation under pedestrian loading.