Cable Force Measurement By Vibration-frequency Method And Research On Cable Damage

As an effective construction member, cable is increasingly used in the long-span spatial structures. Cable has the problem of form finding and force finding as a flexible member in the construction process, which is different from rigid member. The form and force of the cable depend greatly on the stretching process. So we must find effective way to monitor the force change of cable during the stretching process to ensure the safety of construction. At the same time, cable will be subjected to the prestressing loss due to relaxation and damage, which will have unfavorable effect to the safety of structure. So it's important to conduct a real-time monitor of cable force during the work state to ensure that it's in a regular shape.In order to satisfy the demand of project, we carried out the research work on the feasibility of a new type of wireless sensor system, which bases on the vibration-frequency method and is more suitable to the measurement application in large-span spatial structures compared to the wire sensor system. Concerned about the application of the new type of wireless sensor system, the main contents of this dissertation are described as follows:1. The paper summarized the principal of the vibration-frequency method to measure cable force, introduced the linear vibration theory of cable, proposed the practical formulas to calculate the cable force considering the cable sag and bending stiffness effects, and designed corresponding calculation cases to verify the accuracy of the formulas.2. The paper participated in developing a new type of wireless sensor system to measure cable tension force, illustrated the hardware components and programme circuit of the system, and introduced the analytical theory of the structure vibration measurement. The paper applied wireless sensor system to monitor the construction process of chord-tension truss model experiment of Beijing Observatory's FAST project to ensure that the tesion rods were prestressed to the design stress.3. Through the measurement of the cable tension forces in the construction process of the Beijing's north platform model experiment, we proved the feasibility and superiority of the wireless sensor system, and obtained cable tension forces in different construction stages and load cases.4. The paper introduced the damage theory of cable, defined the damage by three parameters: position, extent and intensity, and presented an analysis of damage effects on the statics and dynamics of suspended cables by building calculation models with different damage conditions. We also carried out the research work about the interactivity of cable in the spatial structures by simulating the condition through experiment that how the force of other cables changed when one cable was subjected to damage, and suggested a static strategy based on cable force measurement to detect the cable damage.5. The paper summarized the test and monitor methods of cable in common use and concluded that the most effective way to test and monitor the cable damage is to develop an intelligent cable which has both load-bearing function and self-detection function.