Triple-girder model for modal analysis of cable-stayed bridges with warping effect

In the modal analysis of cable-stayed bridges using the finite element approach, the single-girder model or the double-girder model is often adopted for modeling the bridge deck. These two models are simple and easy to embody in commercial software packages, but the warping stiffness (constant) of bridge deck cannot be properly taken into consideration. This paper thus presents a triple-girder model consisting of one central girder and two side girders symmetrically connected to each other by transverse links. The proposed triple-girder model can easily consider the warping stiffness and other section properties of the bridge deck, and at the same time keep the user-friendly features in the single-girder model. The Nanpu cable-stayed bridge, built recently in China, is then taken as a case study to verify the rationality of the proposed triple-girder model through a comparison with measured data. The study shows that the modal properties of the cable-stayed bridge obtained from the modal analysis using the triple-girder model are more reasonable and close to the measured data. Further studies of four more cable-stayed bridges in China highlight that the extent of the warping effect depends greatly on the type of bridge deck and on the type of bridge tower-cable system. A simple approach for estimating some section properties of typical open-section decks is also suggested to further facilitate the use of the triple-girder model.