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 appr oach, the single-girder model or the double-girder model is often adopted f or modeling the bridge deck. These two models are simple and easy to embody in commercial software packages, but the warping stiffness (constant) of b ridge deck cannot be properly taken into consideration. This paper thus pre sents a triple-girder model consisting of one central girder and two side g irders symmetrically connected to each other by transverse links. The propo sed 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 rati onality of the proposed triple-girder model through a comparison with measu red data. The study shows that the modal properties of the cable-stayed bri dge obtained from the modal analysis using the triple-girder model are more reasonable and close to the measured data. Further studies of four more ca ble-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. (C) 2000 Elsevier Science Ltd. All rights reser ved.