PRACTICAL FORMULAS FOR ESTIMATION OF CABLE TENSION BY VIBRATION METHOD

The vibration method is usually used for field measurement of cable te nsion during the construction of cable system bridges such as an arch bridge stiffened with inclined cables or a cable-stayed bridge. Practi cal formulas for the vibration method are proposed herein taking the e ffects of flexural rigidity and sag of a cable into account. The formu las are based on the approximate solutions of high accuracy for the eq uation of inclined cable with flexural rigidity. Cable tensions are ea sily estimated by these formulas using measured natural frequencies of low-order modes. The practical formulas presented herein are applicab le to various cables, regardless of length and tension as far as the v ibration of first- or second-order mode is measurable. As to a very lo ng cable that cannot be easily excited artificially, a formula is pres ented by using natural frequencies of high-order modes obtained from s tationary microvibrations. The accuracy is confirmed through compariso n of the values obtained by practical formulas with measured values an d calculated values by the finite element method.