Study On The Reasonable Collection Frequency And Evaluation Method Of Health Monitoring Data For Small And Medium-Sized Span Girder Bridges

Small to medium span simply supported girder bridges have a simple structural system with well-defined forces and a relatively large live load response during operation.For small and medium span girder bridges with health monitoring systems installed,it is important to set the acquisition frequency of the sensor system to obtain the integrity of the structural response under live load.This paper relies on the Chongqing Science and Technology Commission’s Science and Technology Project "Research and Application Demonstration of Practical Safety Monitoring Technology for Small and Medium Span Highway Bridges Based on Live Load Characteristics",and uses reliability theory and signal analysis time domain analysis methods to estimate the reasonable acquisition frequency of the structure and to verify its reliability.The relevant factors affecting the reasonable acquisition frequency were discussed,and an empirical formula for the reasonable acquisition frequency of the response of mid-span sections was obtained based on multiple regression analysis,and the feasibility of the method was verified through model tests.The main research contents and conclusions are as follows:(1)The research status of health monitoring contents,monitoring techniques and response acquisition frequency of small and medium span bridges at home and abroad is summarised.According to the structural vibration theory,modal analysis and finite element modelling were used to compare the main beam response under the action of moving mass model and moving spring mass vehicle model in the vehicle-bridge coupled system.The ANSYS modelling analysis is compared with the reference data to verify the validity of the finite element analysis in this paper.(2)Based on the probability integral method of structural reliability and time domain analysis method,the concept of collection frequency reliability and reasonable collection frequency is proposed for the finite element calculation results.A method is proposed to determine and evaluate the reasonable acquisition frequency based on the respective characteristics of amplitude spectrum and power spectrum estimation methods in the time domain signal analysis of bridge span section deflection and strain.The method uses the power spectrum estimation to determine the reasonable acquisition frequency and the amplitude spectrum estimation to compare the digital characteristic errors of the reasonable acquisition frequency signal with those of the quasi-static signal,and to verify the reliability of the acquisition frequency.(3)The determination of relevant parameters in the multi-factor analysis is analysed to investigate the extent to which different influencing factors such as vehicle speed,bridge span,body weight,bridge fundamental frequency and vehicle lateral position affect the reasonable acquisition frequency of span deflection and strain signals.Based on the correlation analysis,the influence degree of different influencing factors is ranked and the empirical formulae for the reasonable acquisition frequency of structural response are proposed based on the multiple linear regression method.SPSS software is used to verify the correctness and reasonableness of the proposed empirical formulae.The suggested values of the reasonable collection frequency are given for the relevant parameters of simple-supported T-beams commonly used in highways.(4)To carry out experimental research on the reasonable collection frequency of simply supported girder bridges,the deflection and strain response time curves of key sections in the span were obtained through the model bridge sports car test;the conformity of the finite element calculation results with the test results was compared and analysed to verify the feasibility of the reasonable collection frequency determination and evaluation method proposed in this paper.Based on the reasonable acquisition frequency determination method,the reasonable acquisition frequency values of the model bridge were calculated and resampled.The results of the resampling of the reasonable acquisition frequency were compared with the measured peak response values,indicating the feasibility of the reasonable acquisition frequency calculation and evaluation method proposed in this paper.The results show that the peak response values are less inaccurate than the measured values if resampled at high frequencies,and more inaccurate than the theoretical values if resampled at low frequencies.