| With the rapid development of long-span suspension bridge,steel truss girder as the main structure of suspension bridge,its fatigue problem is critical for the safe operation of the whole structure.There are many steel truss members,which results in a large number of joint connections,including welding and bolting,leading to outstanding fatigue problems.This article takes Guizhou Qingshuihe Bridge as the research background,and makes reasonable use of various monitoring contents.Through the dynamic weighing system,the statistical characteristics of the vehicle and the fatigue load model were studied,and the fatigue strength of the steel truss girder was checked;Using the statistical characteristics of vehicles,the random fleet is simulated by Monte Carlo to evaluate the fatigue life of steel truss members;Finally,based on vehicle monitoring data,the fatigue time-varying reliability of the members is analyzed,and based on other monitoring content(strain,Boom tension,beam displacement,etc.)to modify the reliability index,based on this,a set of steel truss fatigue warning and corresponding maintenance programs are proposed.The main research contents are as follows:(1)Derivation of fatigue load model.The related theory of fatigue assessment and the main ways to obtain the fatigue load at present are introduced,which leads to the engineering background and the operation and data collection of the health monitoring system in this paper.analyzed the whole year data of the vehicle dynamic weighing system of the bridge in 2017 from the aspects of time,space and load,and based on this monitoring data,combined with the Madis Civil bridge finite element model,and based on the linear fatigue cumulative damage theory,the fatigue load spectrum and a standard fatigue vehicle suitable for the bridge and even for a certain area are derived.(2)The strength check of steel truss members which are prone to fatigue damage.In this paper,the fatigue codes of UK,USA,Europe and China are analyzed in terms of loading mode and loading frequency,and a finite element model of simply supported beam bridge is established to compare the fatigue damage ability of each fatigue load model to steel members.Based on moving load analysis,different types of fatigue-prone members are initially selected,and then according to the fatigue load model I given in the relevant codes of our country,the members with greater fatigue damage are further selected as the fatigue control members of the bridge.The fatigue strength of the screened fatigue control members was checked by the fatigue code in China and the fatigue load model derived in this paper.The results show that the fatigue design of the steel truss of the suspension bridge meets the requirements.(3)Research on the fatigue performance evaluation method of members based on dynamic weighing system.Based on the statistical analysis of the probabilistic model of each parameter of the vehicle based on the traffic monitoring data,the random process of the real vehicle is simulated based on the Monte Carlo method,and used as the fatigue load to evaluate the fatigue life of the control member.The results show that the fatigue life of steel truss beam is greater than the design service life of bridge considering the increase of traffic volume.The cumulative fatigue damage in this case is regarded as a near real damage situation.Based on the principle of damage equivalence,the fatigue load model which does not consider the multi vehicle effect in Chapter 2 is modified.This paper proposes using a two-car model for loading,analyzing the cumulative damage of members caused by different loading intervals,and finding the optimal loading interval.The results show that in order to get the closest to the actual fatigue damage,it is necessary to distinguish the types of members and formulate different loading intervals.(4)Calculation of time-varying reliability of member fatigue.From the perspectives of qualitative and quantitative,the destructive analysis method is used to analyze the importance of fatigue members to the whole structure with stress as the sensitivity index.The research shows that the importance degree is positively related to the magnitude of the stress.The theory of structural reliability and the calculation method of fatigue reliability index are introduced systematically.The time-varying reliability index of important members of the steel truss of Qingshuihe Bridge is calculated using vehicle monitoring data and the bridge finite element analysis model.(5)Research on fatigue warning and steel truss beam maintenance scheme based on reliable indicators.Bridge inspection methods and technical grade assessment methods are described in detail,and the main points suitable for inspection and technical grade assessment of steel trusses for suspension bridges are summarized separately.Based on the accumulated fatigue damage and fatigue time-dependent reliability indicators of the member,research on the dual fatigue warning method is carried out.By summing up relevant literature and standard requirements,the red,orange,and yellow three-level warnings are formulated according to the urgency,and related management and maintenance programs are formulated for different warnings.(6)Research on reliability index modification of member based on other monitoring data.In this paper,based on the monitoring data of strain,vertical displacement of main girder,inclination and suspender tension,the correction method of calculating reliability index based on vehicle monitoring data is proposed.The correlation between each monitoring content and stress is studied.This paper proposes to consider the initial weight of each input data and the method to calculation.The artificial neural network is used to modify the reliable index.For different methods to modify the reliability index,this paper proposes to use AHP to calculate the modified weight coefficient.The results show that the reliability indexes of the members after modification are all reduced,but on the whole,the fatigue reliability of the members of the steel truss girder meets the requirements in recent decades.Based on the health monitoring data of Qingshuihe Bridge,this paper derives the fatigue load spectrum and a standard fatigue vehicle,provides the basis for the fatigue assessment of the bridge or certain area,and check the fatigue strength of steel truss members using this model.The results show that the fatigue design of the steel truss meets the requirements;Feature analysis of vehicle monitoring data,and evaluation of fatigue life of steel truss members by simulating random vehicles using Monte Carlo method,and proposed a two-car loading model for the standard fatigue load model.The results show that the fatigue life of the members is greater than the bridge service life;For the purpose of scientific maintenance of steel truss girder,the fatigue time-varying reliability analysis of the members is carried out.Warning based on reliable indicators and corresponding maintenance strategies are formulated to achieve the purpose of reducing the maintenance cost and improving the maintenance efficiency. |
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