Estimation Of Tension Force Of Prestressed Strand Based On Frequency Testing And Piezoelectric Impedance Technologies

The prestressed concrete continuous box girder bridge, which has been widely used in bridge construction in China, has great superiority in economy rationality and construction technology. However, the cracking of girder webs that caused by main girder’s lack of vertical prestress has seriously affected the operation and development of this bridge type.In order to supervise the quality of vertical prestressed tendons during the construction, and to prevent the cracking of web caused by excessive loss of the vertical prestress, a set of convenient, accurate and reliable detective method and a further developed corresponding standard for site inspection and quality assessment are needed. Thus, this paper conducts the following researches:(1) On the basis of the fact that the stiffness of the vertical prestressed tendons’ exposed section would change with tension, this paper modeled two mechanical models---variable cross-section stiffness coefficient model and variable angle stiffness model, and elaborated the principle of the prestressed tendons’ tension test based on the method of frequency test. Moreover, this part deduced Euler beam theory and Timoshenko beam theory, and obtained the vibration equation of the screw thread steel’s exposed section by utilizing this two theories and substituting the boundary conditions from the two models;(2) Introduced the characteristics and parameters of piezoelectric materials, on the basis of whose unique piezoelectric effect the piezoelectric equation of motion is established. And then this paper deduced the impedance value formula of piezoelectric ceramic structure coupling system, based on which this paper expounded the principle of the prestressed tendons’ tension test based on piezoelectric impedance technology;(3) Designed and carried out the experiment of prestressed concrete on the basis of test principle and the vibration equation of prestressed tension. This part analyzed the self-vibration frequency of different lengths of the exposed sections under different tensions and obtained the model’s stiffness through the vibration equation. And then the paper fit two kinds of function to express the relationship between frequency and stiffness as well as stiffness and tension. In addition, the paper proposed and reviewed the calculation formula of tension based on the fitting function;(4) Carried out the tension test experiment by utilizing piezoelectric impedance technology. Piezoelectric ceramics’ impedance signals collected from anchor end at different position were calculated by impedance index, by which the sensitive position of piezoelectric ceramics was found and the changing regulation that the impedance index varies with tension variation was figured out.