Study On Serviceability Evolution Law And Condition Assessment Method For High-speed Railway Bridge Substructure In Cold Regions Based On Modal Parameters

With the rapid development of high-speed railway in China,the bridge engineering in severe cold regions is continually planning and construction,and therefore,the effect of freezing and thawing on the service state of substructures has become a hot topic in the academic and engineering circles.As an important indicator of the service performance of substructures,the modal parameters can be used as the basis for its’state assessment.Due to the change of the stiffness and constraint condition about substructures,modal parameters show a periodic evolution under the action of freezing and thawing.However,since there are rare researches considering the influence of freeze-thaw action about the service state evaluation of bridge substructure,it is easy to lead to misjudgment in cold regions.Based on the background of Harbin Dalian high-speed railway multi span simple supported(MSSS)bridge,the main works of this paper are as follows.1.The modal identification method for Harbin Dalian high-speed railway MSSS bridge was studied.Based on the comparison and analysis of the principle of the impact vibration test method(IVTM)and the stochastic subspace identification(SSI)method and their respective advantages in the modal identification,this paper put forward the modal identification process of high speed MSSS bridge and carried out numerical verification and field test.Finally,the difficulties in modal identification of high speed railway bridges by conventional test methods were analyzed,such as residual vibration method and pulsating method.2.The periodic evolution law of the natural frequency about high-speed railway bridge substructure in severe cold regions was analyzed.This article carried out the research about the evolution mechanism of high-speed railway bridge substructures’ natural frequency under the action of the freezing and thawing,which was verified in the numerical simulation.The distribution law and its evolution under freeze-thaw was explored by the analysis and summary of a large number of measured sample data.3.The service condition assessment method of the high-speed railway MSSS bridge substructure in the severe cold regions was proposed.The standard value formula of the pier natural frequency was established by the regression analysis method which is based on numerous sample data of the substructure natural frequencies.And the effects of freezing thawing factor were considered.According to the limit value of the bridge service state index,the dynamic assessment criteria for the high-speed railway MSSS bridge pier were proposed,for which the evaluation procedure was finally summarized.