Abstract
An improved analytical solution was developed for the free torsional vibration of suspension bridges. The proposed method considers the warping-torsional shear effect of a stiffening truss as well as gravitational stiffness effects. The equivalent sectional constants such as the shear coefficient, the warping moment of inertia and the torsional constant are precisely formulated based on the thin-walled beam theory, taking shear deformation into consideration. The suspension bridge element is also developed as an extension of the suggested analytical formulation using Hermitian polynomials for finite element procedures. The validity and accuracy of the proposed methods are demonstrated through the numerical examples and, in addition, the effects of the warping-torsional shear deformation and gravitational stiffness on torsional vibration are addressed. In this process, the phenomenonof double root frequencies, i.e., two differentmodes at the exactly same frequencies, was newly identified for the torsional free vibration of a simply supported suspension bridge in analytical approaches.