Evaluation of tension force using vibration technique related to string and beam theory to ratio of moment of inertia to span

摘要

Evaluation of strength of cable using vibration method is widely applied on the bridge health monitoring. The vibration method is based on the natural frequency recorded from cable that used to estimate the strength of cable on cable stayed and suspension bridges. Many practical formulae to estimate cable tension using natural frequency have been proposed. The cables applied on the bridge have the variation of moment inertia to length. The calculation of strength of cable based on the flat taut string theory ignores the sag-extensibility and bending stiffness of the cable. On the other hand, the beam theory includes the parameter of bending stiffness to compute the natural frequency of beam. The specimen used in the laboratory experiment is the strep steel. The section properties of the specimen were 2 mm of thickness, 38.5 mm of wide and 1000 mm of length respectively. The ratio of the moment of inertia to length of the specimen is 9.15. The investigation shows that the experiment result is closed to the analytical solution by using string theory. In addition, the results of the beam-string, stoke, and irvine theories are closed to each other, but quite different from the experiment result. Adopting the flat taut string theory and the beam theory, this paper shows the compatibility cable behaviour that is close to the beam or string based on the moment of inertia to length ratio.