| Structural health monitoring system is an important security measure for ensuring that the prestressed construction and healthy operation of the large span spatial structure safety, it would be the extreme conditions structural failure warning to minimize personnel and property losses. During construction and operation of the external loads (wind, earthquake, temperature, etc.) prestressed large-span spatial structure can work well enough just as the structure of external load effect (displacement, acceleration, stress, fracture, etc.). It is an important indicator of whether the structure health, and also the important content of structural health monitoring. Prestressed large-span space structures are mainly prestressed lattice grid structure, that was inclined column net structure, the cable dome structure, the dual-direction beam string structure, the prestressed cable in these structures, the tensioning construction completed and so on After the completion of the initial condition, using the completed stage of whether meet the requirements of design, structure of the cable force and internal force level after disasters such would be more safety than before.In the process of prestressed cable,cable tension will make the mutual influence between the cable:each time the tension will almost always make previously tension cable force changed, make the structure of cable force deviate from the designed value, cause the loss of controlled cable force. Cable in use process, working cable occur stress relaxation and cable damage resulting in loss of stress prestressed cable, causing the cable force uncontrolled. The uncontrolled cable force causing the internal force of the structure redistribution, and even lead to failure of the whole structure. So the accuration measurement of cable force of prestressed cable structure is the key technology to ensure engineering safety.At present, the process of prestressed cable construction have pressure meter test method and pressure sensor measurement to measure cable force, basically can ensure the test precision. The cable force measurement method of working cable usually have pressure sensor method, force balance method, frequency method (vibration), magnetic flux method, optical fiber grating. Pressure sensor method must use a pressure sensor in each end of the anchor cable, which is very expensive; Force balance method of flexible cable only on a smaller section has high measuring accuracy; Magnetic flux method will be pre-worn sensor on the cable, the application without embedded sensor cable can not be the law; The fiber grating method cost is too high to apply the detection of cable in service. Therefore, considering the economic and technical aspects, frequency method with test instrument miniaturization, portability, easy installation, can be used repeatedly, and the accuracy is very high, so the best choice of frequency master cable force testing.For the stout prestressed cable structure cable and multi span cable force test difficult problem, this paper analyzed the testing theory of cable force based on the frequency of sinusoidal excitation fitting method. Firstly, different boundary conditions and the cable vibration dynamic model of cable stiffness conditions are solved, and derived the calculating formulation of cable force; and then the cable force on the dual-direction beam string structure are calculated, and to analysis the results, to verify the applicability of multi-frequency quasi legitimate; the last cable safety monitoring system is developed based on the theoretical results. Firstly, different boundary conditions and the cable vibration dynamic model of cable stiffness conditions are solved, and derived the calculating formula of cable force; and then on the dual-direction beam string structure are calculated, and the results of the analysis, to verify the applicability of multi frequency quasi legitimate; In the end, cable safety monitoring system is developed based on the theoretical results. |
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