Research On The Health Monitoring System And Its Key Technics For Long-span Roof Space Latticed Structure Of Shenzhen Citizen Center

Health monitoring of magnitude structures is important for industry, since it can ensure the safety assessment of engineering structures during their service life. It is inevitable that load long-term effects, fatigue effects and unpredictable accident effects bring out structural damage accumulation and carrying capacity decline, consequently resistant capacity of nature disaster descending influences employ function and eventually causes tragedy accident in extreme situation. The wind effects on these long-span structures play an important role. The wind pressure or suction in the upright direction which include mean wind pressure force and the fluctuating wind pressure force distributes on the long-span roof spatial lattice structure actuated by the natural wind over typical urban terrain. Many spatial lattice structures are prone to severe damage subjected to the strong wind. Although such kind of damage never resulted in the structure's collapse, it would badly influence the structural service life, moreover, with the accumulation of damage, the whole structural collapse or failure would ultimately occur. Therefore, it is necessary to establish the health monitoring system of long-span complex roof spatial lattice structure under wind-excited and capture real-time work status of the roof spatial lattice structure and diagnose damage components in order to ensure the service life and safety.Taken the roof of Shenzhen citizen center that is the biggest spatial steel latticed structure in the world as the engineering background, the design principles and key techniques of health monitoring system for large span complex spatial latticed structure under wind-exciting are discussed in detail in this thesis. As well as, it realized automatic alarm of the work status of spatial latticed structure, automatic diagnosis of unknown damage and real-time safety assessment for damaged latticed structure from the limited data-acquisition. Therefore, the key techniques and innovations are proposed in the thesis who are lised as follows,(1) In order to establish the favorable groundwork for accuracy of health monitoring system, the optical fiber Bragg grating sensing system with the advantages of non-invasiveness, electromagnetic immunity and high resolution is adopted partly. The key techniques are included, the Ethernet communication manner that is utilized to transmit interrogation signal by Si-425 interrogator to the database server, since the reflection wavelength of optical FBG sensors can be interrogated and be stored in the interrogator by Si-425 interrogator. Therefore, the data-acquisition based on optical FBG sensors can be obtained real-timely by health monitoring system. Furthermore, the multithreading technique is adopted to obtain the data from interrogator, in order to improve the computers efficiency and real-time data-acquisition.(2) In order to acquire the work status of the whole spatial latticed structural rods by data-acquisition based on finite sensors, the basic idea is adopted by the intelligent monitoring subsystem of the roof spatial latticed structural work status that is list as follows, step1: to identify the wind load; step 2: to update the structural finite element model; step 3: to measure peak factor of structural response; step 4: to directly analyze the structural real timely response. The real-time structural response under wind-excited can be obtained based on the idea. It is very difficult for real-time process of these three parts by reason of large calculation cost, which are wind load identification, structural finite element model updating and structural real-time response analysis, due to Shenzhen citizen center roof spatial latticed structure with huge size. The structural work status assessment process is divided into two parts including "nonreal-time" processing and "real-time" processing. The data are in store from the "nonreal-time" processing analysis in advance. The work status assessment is achieved by simple analysis based on calling between "nonreal-time" data and "real-time" data. The action of the intelligent monitoring subsystem of the roof spatial latticed structural work status is executed in every 10 minutes; the maximum response of structure rods in these 10 minutes can be simply calculated. The key techniques are consisted by these; the weighted proper orthogonal decomposition technique is adopted to identify the characters of wind pressures at all internal nodes on the truss structural roof in the frequency domain by using the measured wind pressure data from non-uniformly taps. Moreover, by using information from finite acceleration sensors with optimal placement on the structure, the accurate analytical model of the structure is established by updating the finite element model based on modifying node parameters. Then, the monitoring result of entire truss structure in the worst working performance in every ten minutes is obtained according to positive deductive method with the measured mean wind speed and wind direction from anemometer respectively and peak factor acquired from finite strain sensors on the truss structure in every ten minutes.(3) In order to obtain the whole spatial steel structural stress field with finite strain gauges, the fuzzy pattern recognition method is adopted in this paper to identify directly the instantaneous stress filed of steel structure by using instantaneous strain characteristic vector acquired from finite strain gauges fixed at the key points. Firstly, to select some key points which are sensitive to load and its position on the spatial steel structure. Secondly, to establish the relationship between the key points' strain and the structural stress field mode after the instantaneous load can be recognized by the key points' strain on the spatial steel structure. Thirdly, to confirm the strain of key points corresponding with the mode of stress field and then the fuzzy subset of each stress field mode can be obtained on the domain. Finally, to calculate the approach degree of unknown stress field with respect to all stress field modes, identified stress field with largest approach degree is considered as actual stress field of the structure. The key techniques are listed as follows, the stress field pattern database can be established on the graded the load by the steel bracket. It is feasible to establish the one-to-one relationship between the limited key points' strain and the bracket's stress field pattern, and the key point's strain can represent the characteristics index of bracket's stress field.(4) The roof spatial latticed structure of Shenzhen citizen center is supported on the steel brackets, with the result that bearing capacity will be completely changed once the steel bracket is destroyed. Spatial latticed structure is prone to collapse only duo to destroy of steel bracket. Therefore, firstly, according to combination of the mesurement wind speed, wind direction and response peak factor, the elastic-plasticity calculation of bracing force on the every bracket of the spatial latticed structure and ultimate bearing capacity of every bracket is carried out based on the updated structural finite element model. Then, the damage pattern database of spatial latticed structure is established by calculation of distribution of abruption rods and crippling rods as well as the maximum displacement of node based on positive analysis. Finaly, the maximum displacement of spatial latticed structural node can be obtained by damage pattern of spatial latticed structure based on destroy of bracket, it is used to determine collapse of spatial latticed.The health monitoring system is the advanced and intelligent system applied to the roof long -span spatial latticed structure of the Shenzhen Citizen Center with huge size and very complicated structure in the world. The key techniques of health monitoring system are applied for nation invent patent of China, and it is passed test by the building owner and expert. It is primary exploration and application of safety early warning theory and technique for long-span roof spatial latticed structure under wind-excited.