Cable Force Measurement Method And Condition Identification Theory For Tensile Space Structures

Tensile space structures mainly rely on the geometric stiffness provided by prestressing construction to resist the morphological changes caused by structural loads and to maintain the stability of the structure.Unlike conventional structures,the most important structural properties are stiffness performance rather than traditional strength and stability,and the corresponding structural health monitoring should focus on stiffness monitoring.The cable force measurement technique can be use to determining the prestress distribution of overall structural,to investigate the effect of cable force deviation on structural stiffness,and to obtain the state change of the structure based on monitoring data.The information of structural state change is often submerged under various complex environmental loads,and so that the abnormal state of the structure cannot be accurately identified.The state identification of tensile space structures should be based on accurate measured results of the cable force and effective structural response separation,establish a benchmark model based on the data,and mine the data features that respond to the structural state changes to provide decision makers with accurate information about the performance of the structure.Therefore,this paper is based on the measurement technique of the tensile space structure of the cable force,proposes a structural response separation method for complex kinds of structural loads,and establishes the theory of structural state identification under the whole life cycle,which improve the theoretical system of health monitoring of tensile space structure.The main research contents are as follows.Firstly,the cable force measurement technique is based on the basic concept of material mechanics,which can be used to obtain the corresponding cable force value by measuring the surface strain and then converting it,thus solving the problem of long-term measurement of large-scale cable force.By using theoretical derivation and numerical simulation,the relationship between surface strain and cable force is investigated,and the calculation method of cable force considering correction coefficient is proposed.A reliable cable force measurement equipment was developed,integrating sensing unit and acquisition unit to realize the wireless acquisition and transmission of cable force monitoring.A calibration test was designed to verify the feasibility and accuracy of the cable force measurement equipment.The average relative error of the measured cable force does not exceed 2%.Secondly,a structural response separation method under the action of complex multi-source loads is proposed,which uses the overall average empirical modal decomposition（EEMD）for structural response expansion and independent principal component analysis（ICA）for structural response signal separation,which achieves reliable identification of complex load quantities without relying on load a priori information,and adaptive separation to obtain the responses of various types of structural load actions.The relative root means square difference(R_RMSE)is introduced to adaptively determine the algorithm parameters in the calculation process of the EEMD algorithm,and the Bayesian information criterion（BIC）is improved to solve the computational overflow problem of the ICA algorithm in the determination of the number of load sources.The finite element simulations of typical cable-net structures are used to verify the effectiveness and accuracy of the method.The differences in response separation performance between the existing methods and this paper are compared,and the effects of measurement noise and monitoring time length on the separation results of different types of load effects are discussed.The results show that the EEMD-ICA^*algorithm proposed in this paper has better separation performance than the existing methods.Thirdly,a structural state identification method based on Gaussian process regression is developed.The method considers two different cases of one-dimensional input and multidimensional input,and constructs a benchmark mathematical model of the structural response to obtain the modeling residuals between real and predicted data.By analyzing the modeling residuals,a structural state anomaly state indicator based on the Kolmogorov-Smirnov test and Euclidean distance is proposed to identify the moments when the structural state may change using the sliding window strategy.The temperature load effect in the concrete strain data under the action of temperature cycles is extracted,and the structural state identification method considering one-dimensional input is validated.The cable force response of this cable-net structure of Hangzhou Gymnasium is simulated,and the effects of different input combinations on the structural state identification results are discussed.The results show that considering the structural response separation and setting reasonable input combinations and noise distribution improve the modeling accuracy of the structural response and ensure the reliability of the state identification.Finally,using the Beijing National Speed Skating Oval,a typical cable-net structure,as the application object,the work of structural response measurement,structural response separation,and structural state identification was carried out.A comprehensive and reliable wireless structural monitoring system was designed to monitor the key structural changes during the construction and operation and maintenance phases,and typical structural response data were obtained for different phases.Based on the measured results of the response of the cable-net structure,various types of load effects in different stages are separated and the correlation between the components in different regions is investigated.Based on this,the structural state identification was carried out by considering one-dimensional input and multi-dimensional input respectively,and the structural response of two typical periods（six months after the tensioning of the cable-net and a strong snowfall）,was used as an example to analyze the changes of the structural state.The results show that the average relative deviation between the field measured cable force results of the National Speed Skating Oval and the reference method is within 5%;the structural response separation algorithm reveals the change law of the force performance of each area of the structure under the typical construction load;in the case of abnormal changes in the response,the GPR-based state identification method excludes the interference of environmental loads and provides accurate structural state identification results.