Issue 38

P. Lonetti et alii, Frattura ed Integrità Strutturale, 38 (2016) 359-376; DOI: 10.3221/IGF-ESIS.38.46 361 B RIDGE FORMULATION : MAIN EQUATIONS AND INITIAL CONFIGURATION he structural scheme, reported in Fig. 1, is consistent with a self-anchored cable-stayed suspension bridge, in which the cable system is based on the combination of suspension and cable-stayed configurations. Suspension and cable-stayed cable systems consist of a double layer of cables arranged in the planes containing girder and pylon extremities. Figure 1 : Structural scheme of the self-anchored cable-stayed suspension bridge. In particular, the cable-stayed system is based on discrete stays, which are mainly arranged in the region close to the pylons, whereas, the suspension system is composed by a main cable and several hangers located in the central part of the main span. The hanger rods and the stays are hinged, at both ends, to the girder and to the main cable or to the girder and pylons and they are spaced at constant step G  along the entire girder length. Furthermore, the stays are spaced at constant step P  along the pylon height and, depending on this step size, the cable-stayed system can be characterized by a fan, a semi-fan or a harp configuration. The main cable is in the central span only and it is hinged at top of the pylons. The cable system is completed by anchor cables, which connect stiffening girder extremities to the top of the pylons. The stiffening girder is simply supported at its ends and at the pylons connections, which are formed by H-shaped configurations. Initial configuration of the bridge The initial configuration of the bridge is obtained by using the zero displacement method, which identifies girder and pylon profile under permanent loading by adjusting the initial cable forces to give zero-displacements at the cable anchorages. With reference to the scheme reported in Fig. 2, the unknown quantities are represented by the post- tensioning stresses in the cables ( , , ) S H M i i S S S which are designed by means of the following relationship: 1 1 [ , , , , , , ] C S S H H M S H N N S S S S S S     (1) T