Research On Health Monitoring And Safety Assessment Of Large-Span Steel Structures

Long-span spatial structure is widely used in large-scale public buildings.With the increase of the service life of the structure,under the influence of material deterioration,environmental erosion and random load,the structure will inevitably be damaged.Once a safety accident occurs,it will not only seriously threaten the safety of people’s lives and property,but also cause serious negative social impact.In order to prevent the occurrence of existing structural safety accidents,structural health monitoring systems have been established for large-scale projects at home and abroad,and it is particularly important to evaluate the safety and health status of long-span spatial structures through the monitoring system.Thus,combined with an engineering example,starting from the stable,safe and healthy state of spatial structure in service,the necessary and sufficient mechanical condition criterion of instability and the critical load and critical stress of instability are derived by using catastrophe theory.The stability of spatial structure is analyzed from the point of view of energy distribution,and the mechanism of energy entropy change and the calculation method of overall stability of spatial structure under external load are discussed.In this thesis,the comprehensive evaluation method of spatial structure health status based on structural health monitoring system is studied.The main research contents and innovations of this thesis are as follows:（1）The health monitoring system established by the actual structural engineering is summarized.The structural modeling is carried out by the finite element software,and the mechanical properties of the steel roof are analyzed,which provides a theoretical basis for the arrangement of sensors in health monitoring.According to the actual in-service environment of the building structure,the appropriate sensor is selected and the sensing system is established.（2）In this thesis,the problem of local instability of spatial structure is studied by using simple compression bar mechanical model,energy principle and catastrophe theory.The nonlinear analysis mechanical model of the truss under axial force is established,and the critical load and critical stress of local instability of spatial structure are derived.The critical load is analyzed when the structural elastic modulus and the ratio of length to diameter are taken into account.According to the relation of critical load,the influence of local truss on the stability of spatial structure under external load is analyzed from the point of view of mechanics.When the external load P increases from 0 to P_cr,the local structure is always in a stable state;when P>P_cr,the local structure jumps in the stable state and the equilibrium state changes abruptly.In order to keep the local structure in a stable state,it is necessary to ensure that the load it bears is less than the critical load.（3）The concept of structural strain energy entropy is proposed,and the catastrophe criterion of structural strain energy entropy is established by using catastrophe theory.Through the application of the energy entropy catastrophe model based on the strain energy distribution,the basic law of the evolution of the overall stable state of the structure under the control of the order parameters of the strain energy distribution is revealed.When the strain energy entropy of the structure decreases,the overall force distribution of the spatial structure is uneven and the stability decreases.（4）The concept of spatial structure health index is put forward,and the index system of long-span spatial structure is established according to the previous research results and the selection principle and system framework of the research object in this thesis.The comprehensive evaluation method of the health state of spatial structure is studied based on multi-sensor data fusion.By using the monitoring data accumulated by the monitoring system,the monitoring data of the same type of sensor can be extracted effectively,and the characteristics of the monitoring data can be determined reasonably.The fuzzy comprehensive evaluation method is used to quantitatively evaluate the health state of existing structures,the effectiveness of the proposed method is verified by practical engineering examples,and the structural health index is given quantitatively.It plays a certain role in improving the structural health monitoring system,evaluating the performance of existing buildings and ensuring the safety of engineering structures.