M V Sardesai, Dr A K Desai / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 4, Jul-Aug 2013, pp.1424-1429 1424 | P a g e Investigation Into Cable-Structure Interaction For Extradosed Bridge M V Sardesai*, Dr A K Desai** *(Ph.D Research Scholor, Sardar Vallabhbhai National Institute of Technology, Surat ** (Professor, Sardar Vallabhbhai National Institute of Technology, Surat ABSTRACT Cable supported Bridge structures have distinctive dynamic behavior compared to any other type of bridge, especially the dynamic behavior. Support excitations sets structure to vibrate; cable excitations can be caused by rain, wind or stochastical vibration due to plying vehicles or due to vibration of deck. In modern cable-stayed / Extradosed bridges, the stay cables are often closely spaced, with the cable lengths and tensions gradually varying from position to position. The natural frequencies of their self- vibrations are therefore likely to be rather closely placed as well. Such boundary-induced vibrations of the stay cables are likely to complicate the overall dynamic behavior of the bridge. The paper focuses on dynamic behavior of Extradosed Bridges, dynamic behavior of Extradosed cables and possible interaction resulting into coupled mode of vibrations. Keywords - Extradosed cable stayed bridge, Earthquake, Dynamic response, cable-structure interaction I. INTRODUCTION A) Extradosed Bridge The recent research has shown that a Extradosed bridge, variant of cable stayed bride where cables add substantial prestress to the deck because of the shallow pylon, are found to be economical for spans upto 250m. Figure 1 shows the arrangement of cable for Girder, Extradosed and cable-stayed bridge. The intrados is defined as the interior curve of an arch, or in the case of cantilever-constructed girder bridge, the soffit of the girder. Similarly, the extrados is defined as the uppermost surface of the arch. The term ‘Extradosed’ was coined by Jacques Mathivat (1988) to appropriately describe an innovative cabling concept he developed for the Arrêt-Darré Viaduct, in which external tendons were placed above the deck instead of within the cross- section as would be the case in a girder bridge. To differentiate these shallow external tendons, which define the uppermost surface of the Bridge, from the stay cables found in a cable-stayed bridge, Mathivat called them ‘Extradosed’ prestressing. Some features of Extradosed Bridge as given below;  External appearance resembles cable-stayed bridge – but structural characteristics are comparable to those of conventional girder bridge  The Girder Depth are lesser than that of conventional girder bridges  The stay cables (prestressing tendons outside the girder) need no tension adjustment necessary for cable-stayed bridges, and can be treated as usual tendons as in girder bridges  The height of pylon is half as that of cable- stayed bridge and hence easier to construct  With small stress fluctuation under live load the anchorage method for stay cables can be same as that of tendons inside girder and thereby achieve economy Fig. 1 Cable arrangements in Girder Bridge, Extradosed Bridge and Cable stayed bridge B) Dynamic response Vibrations caused of support excitations has been matter research with some failures (For example Aratsu Bridge, Tenzopan bridge, Erasmus Bridge etc) underlining the importance and need of study of dynamic behavior bridge vibrations as well as cables vibrations. With the rapid increase in span length, combined trend and also trend of using high strength materials have resulted in slender structures and a concern is being raised over dynamic behavior of such structures, in case of cable supported structures it is more pronounced as this further includes vibrations of structure and cable elements also. An accurate analysis of natural frequencies is fundamental to the solution of its dynamic responses. In modern cable-stayed / Extradosed bridges, the stay cables are often closely spaced, with the cable lengths and tensions gradually varying from position to Girder Bridge - Small cable eccentricity Extradosed Bridge – Intermediate Cable-Stayed Bridge – Large cable