A Study On Pedestrian-induced Vibration Comfortability Of Footbridge

Modern footbridges tend to have larger span,and the structure shows the characteristics of less mass and lower damping.In recent years,many footbridges have suffered from excessive pedestrian-induced vibration,which severely influences the walking comfortablity and structural safety.The pedestrian-induced footbridge vibration comfortablity is emphasized by the Bridge Engineering Community and the International Standardization Organization.Literature survey shows that there are large differences in the pedestrian-induced vibration comfortablity index proposed by different research results and standards,and there is either no quantitative study considering the pedestrian endurance capacity,structural vibration response and subjective sensory uncertainty.In this thesis,studies are aimed at the pedestrian-induced footbridge vibration comfortablity,quantitative calculation of vibration comfortablity,the real-time measurement and evaluation of vibration comfortablity,the improvement of comfortablity evaluation method,the parameters analysis of structural vibration and the artificial neural network.The main contents of this research include:(1)The concept of “sensitivity” of footbridge vibration is proposed,and the quantitative expression of pedestrian vibration sensitivity is realized.In order to describe the sensitivity better,the concepts of “human body resistance” and “vibration effect” are introduced according to the principle of probability and statistics.Mathematical definition of se nsitivity is put forward.Calculation expressions for a pedestrian and pedestrians are deduced respectively.The results of the sensitivity model are compared with the field test results and the conclusions of ISO,and the correctness of the sensitivity method is verified.(2)The nonlinear relationship between the subjective response membership of pedestrians and the structural vibration response of footbridges is studied.An improved membership function is proposed.The improved membership function is co mpared with the traditional calculation formula,and the experimental results of former reseachers.The comparison results show that the improved membership calculation value is closer to the experimental results than the traditional membership calculation formula.On the basis of the improved annoyance rate calculation model,an approximate footbridge annoyance rate curve is given,whose accuracy meets the requirements of engineering application.The error between the calculated curve and the approximate c urve does not exceed 0.04.A comprehensive evaluation method of footbridge vibration comfortablity considering vertical and lateral coupling vibration is proposed.The vibration comfortablity and vibration reduction design of the Guangzhou Huangpu Science City Footbridge are studied.The calculation results show that the reasonable TMD can play a role in vibration reduction.(3)Based on the built-in high-precision acceleration sensor,orientation sensor and real-time display function of smartphone,a real-time evaluation system of pedestrian-induced footbridge vibration comfortablity is developed.The evaluation system consists of data acquisition subsystem,management center subsystem and smartphone client.The spatial coordinate transformation principle is applied to the dynamic signal acquisition process,and the transformation from the smartphone coordinate system to the inertial coordinate system is realized;The program of calling the orientation sensor is compiled,which realizes the smartphone to automatically collect and display the current orientation information in real time;On the basis of removing the trend item,the mathematical morphology method is adopted to correct the drift of vibration signals,and the gravity noise in the raw acceleration signal is filtered by wavelet transform.The test results of the proposed evaluation system and the traditional acceleration sensor are compared,and the field experimental results are compared with the subjective feelings stipulated by the international standard ISO2631-1:1997.(4)Based on the analytical solution theory,the pedestrian-induced footbridge vibration comfortablity is studied quantitatively.The analytical solution of pedestrian-induced vibration response is derived,and the maximum acceleration response under resonance is calculated.The effects of vibration mass,stiffness,damping,span,pedestrian walking mode,walking speed and walking frequency on the acceleration response of pedestrian bridge are analyzed,and the results of acceleration response are compared with those of previous studies.The most significant parameters affecting the acceleration response of the footbridge are obtained through parameter sensitivity analysis.Suggestions for the comfortablity design of the footbridge are proposed.(5)Considering pedestrian walking parameters as input,while peak acceleration as output,a BP neural network for pedestrian-induced vibration comfortablity is established.Based on the measured data,the BP neural network is optimized,and the optimized BP neural network is used to predict the peak acceleration of the footbridge structure.The predicted value is compared with the measured value,adaptive neural network,CMAC neural network,Elman neural network and analytical solution.The vibration comfortablity BP neural network provides a basis for vibration comfortablity evaluation under non-pedestrian-footbridge resonance condition.