Time-varying Reliability Analysis Of Concrete Filled Steel Tube Arch Bridge

Under its unique shape,strong spanning capacity,simple construction and strong economy,Concrete filled steel tube(CFST)arch bridge has been widely used in all parts of China.However,on conditions that its development time is still short and its structure is complex,the research on it is still not deep and perfect enough.Reliability is an important index to evaluate the stability and safety of bridge structures,which can quantitatively analyze the random factors in the process of bridge operation.Based on the time-varying reliability theory,this paper taked a hail-through CFST arch bridge as an analysis example,and combined the performance degradation research results of concrete and steel materials to analyze the change of structural reliability with the increase of bridge service life;Considering the influence of alternating load on fatigue life,the residual life of bridge components was predicted.The main research contents and research results of this paper include:1.The research results of domestic and foreign scholars in the field of structural reliability theory were sorted out,the basic ideas of reliability theory and the advantages and disadvantages of calculation methods were summarized.Combined with the characteristics of research objects,Monte Carlo method was selected as the basic method of reliability calculation.Combined with the characteristics of CFST arch bridge,the main random factors affecting its function were analyzed,including material performance,geometric size,calculation mode,load effect and their distribution.The main distribution types of random variables involved in this paper are normal distribution,logarithmic normal distribution and extreme value type I distribution.2.The main materials of CFST arch bridge are steel and concrete.This paper analyzed the performance degradation process,summarized the law of material degradation,and established resistance degradation models.The degradation of concrete strength and the corrosion depth of steel materials in atmospheric and airtight environments were mainly considered.For the steel wire material in the suspender,a salt spray accelerated corrosion test was carried out.By observing the appearance characteristics and mechanical properties of the steel wires before and after corrosion,the strength and fatigue performance degradation laws of the steel wire was obtained,which provided theoretical and data support for the reliability time-varying process analysis later.3.For the calculation of the time-varying reliability of the research object,the basic idea of this paper is: firstly calculate the time invariant reliability which is the reliability index in the design stage,then combine the time-varying process to obtain the timevarying reliability calculation result.Combined with the current specification,considering the random factors that have a great influence on the bridge operation,taking the limit state of bearing capacity and the limit state of normal service as the main failure modes,the resistance function expressions were established for the main load-bearing members of the half-through CFST arch bridge respectively.A threedimensional finite element model of the CFST arch bridge was established,and load effect standard value of the bridge was obtained by applying different loads to the model,and then the corresponding function was obtained by combining the resistance expression.The Monte Carlo method was used to calculate the function through the MATLAB program,and reliability indexes of the main components of the bridge in the design stage were obtained.The reliability indexes of the components were analyzed,found that the arch rib and column are the most likely failure components of the CFST arch bridge in the design stage,their failure modes are the eccentric compression of the arch rib truss and the eccentric compression outside the column surface.4.Taking the time invariant reliability as the calculation starting point and the resistance deterioration model as the time-varying process,the reliability indexes of the half-through CFST arch bridge at each time point in the service period were obtained,and the time-reliability index coordinate system was established.The time-varying reliability curves of the main components were obtained by numerical fitting with the point diagram.Through the analysis of the time-varying reliability curves,the remaining life of each main component of the research object was predicted.The predicted service life is 47 years for the arch rib,25 years for the suspender,71 years for the column,and 52 years for the steel beam.Among them,the fatigue life of the suspender is the shortest,which is 25 years;the tensile reliability index of the suspender under the limit state of the bearing capacity decreases the most,which is 61.6%.