Structural State Identification Theory And Application Of Railway Steel Truss Bridge Under Quasi Static Progress

Long-term service of bridges are more prone to structural damage under the effect of external load and environmental factors,resulting in a defect in durability and safety,increasing the probability of structural disaster,and threatening the safety of transportation.At present,a certain number of bridges have entered or will enter the late service in our country.In order to respond to the operational safety risks of bridges actively,The operating mode of bridges in our country will change from “construction with neglect management” to “emphasis on both construction and management”,which requires more effective structural safety diagnosis technology of bridges.The structural health monitoring(SHM)system equipped on large bridges contributes to structure state identification and damage diagnosis by means of collecting real-time monitoring data.However,bridge structure safety diagnosis is difficult to break through the bottleneck of “missed diagnosis and misdiagnosis” due to shortcomings of traditional structural health diagnosis theories and methods.Therefore,it is of great significance to study the basic theory and engineering application of service safety diagnosis of bridges.This thesis focuses on the quasi-static process of railway steel truss girder during operation,studying the structural state identification theory using thermodynamics and thermoelasticity.A theoretical analysis framework of structural state identification under quasi-static excitation was proposed.Combined with the real bridge structural health monitoring(SHM)system,a structure state analysis model and state identification method for vertical deformation state and longitudinal deformation state were proposed.(1)In this study,the elastic body is regarded as a closed system based on the theory of thermodynamics.The quasi-static state equation of the elastic body is constructed using the thermodynamic parameters(pressure,strain,temperature).Based on thermoelastic theory,the relationship between displacement-temperature model parameters and structure stiffness was revealed,and the applicable scope of temperature-based structure identification was clarified.The quasi-static input-output model of the structure was analyzed from the perspective of thermodynamics,and a structure state recognition framework for thermodynamic reversible and irreversible processes is established.The proposed framework can comprehensively consider the effect caused by temperature quasi-static load,improving the reliability of structure state identification.(2)Based on the framework of thermodynamic reversible process,structural abnormal detection of a steel truss beam was carried out by using temperature and vertical rotation.First,the state equation of vertical rotation of the structure under the action of temperature and dead load is derived,and the linear model of rotationtemperature-dead load is established.The reliability of the model is verified by a case study.Secondly,an anomaly detection method using double-index is presented by combining the rotation-temperature-dead load linear model with Bayesian theory.Finally,the anomaly detection method is applied to a real bridge.The results showed that the anomaly detection method proposed has the potential of identifying load anomaly and stiffness anomaly.(3)Based on the framework of thermodynamic irreversible process,the longitudinal deformation state of a railway steel truss beam is quantitatively analyzed by using the bearing longitudinal displacement,temperature,and train running information.Firstly,the relationship between input(temperature and train longitudinal force)and output(bearing longitudinal displacement)is established through mechanical model analysis.Secondly,based on the framework of thermodynamic irreversible process,an input-output hysteresis model was established by analyzing the quasi-static path of bearing displacement,and a state index and state identification method were proposed to characterize the longitudinal deformation capability of the structure.Finally,the state identification method is applied to a real-world bridge.The results show that there is a nonlinear hysteresis relationship between the bearing longitudinal displacement and the quasi-static action when the bearing appears to friction slip,and the influence of various quasi-static effects on bearing longitudinal displacement must be considered comprehensively.This study revealed the structure system input-output mechanism under quasistatic excitation,and presented a structure state identification framework with considered multifarious quasi-static excitations.It overcomes the shortcoming of single quasi-static excitation structure state identification method and lays a thermodynamic theoretical foundation for the civil engineering structures health diagnosis under quasistatic excitation.