TENSION ESTIMATION OF ELASTIC CABLES USING VIBRATIONAL METHOD

This paper presents a simplified method for the evaluation of the tension in elastic cables and tendons based on vibrational method. The accuarcy and simplicity of this method is compared with other methods. Force transmitting members in different structures including, cable-stayed bridges, post-tensioned segmental bridges and so on as axially one-dimensional tensioned structures reflect the health of entire system, therefore a rapid tension estimation is needed for condition monitoring. Estimated tension with numerical pre-determined formulas of string theory, beams theory with different boundary conditions are compared with estimated tension conducting mode shape ratios and modal frequencies for multiple measurment. Furthermore, sensor location and mode selection of mode shape functions method is simplified by dominating the first mode to simplify the error function with changing reference sensor location to mid-length as Equation 1.(....)Application examples for four different models show that the accuracy of tension estimation using pre-determined formulas is less accurate in comparison with the mode shape functions method, and requires better estimate of mass and length. In this research three methods are applied on four different FE models using software package ABAQUS and using MATLAB toolbox developed by the authors. The proposed approach was tested on four models studied before as shown in Table 1. In the models 1 and 2, two linear springs are used to simulate the elastic constraints from rubber-torubber distance. The spring coefficients are assessed to find the best fit coefficient for the identified modal frequencies during actual measurements for the first two models (1.0 e+7 N/m for the first model and 5 e+6 N/m for the second model). Five locations at 0.1th, 0.15th, 0.2th, 0.25th, 0.3th and 0.5th of the cable length are chosen to obtain the acceleration responses. Then, the FFT is used to determine the nodal displacement of each node to determine mode shape ratios and effective vibration length as shown in Figure 1.

Keywords:

Tension estimation , Vibrational measurment , Tendon , Elastic cable , Mode shape function , Modal frequency , Least square