Study On Basic Mechanical Properties Of Extradosed And Intradosed Cable-stayed Bridges With Continuous Cables

The Extradosed and Intradosed Cable-Stayed Bridge with Continuous Cables is aninnovative structural system, which is developed from traditional combinedcable-stayed bridge. The pylon height is as low as the traditional extradosed bridgewhile the girder height is greatly reduced and similar to a conventional cable-stayedbridge. Preliminary study shows that the novel structure has advantages of smaller selfweight, larger live load stiffness, better dynamic performance and a notable girder forcereduction, which has great structural improvements compared with the traditionalcable-stayed or combined cable-stayed bridge. However, the systematic research on it isnot yet implemented, and the guiding suggestions for engineering have not been putforward.Based on the practical experience and research on traditional combinedcable-stayed bridges, the basic mechanical behavior of Extradosed and IntradosedCable-Stayed Bridge with Continuous Cables is investigated in this dissertation fromvarious aspects. The main work and achievements are as follow:1) The basic conception of Extradosed and Intradosed Cable-Stayed system ispresented and the innovative cable-girder anchorage is developed. Several cable-strutarrangement schemes in both longitudinal and transverse directions are proposed forbridges with different span lengths and deck widths. The concept of cable-stayed systemefficiency is described from the displacement point of view, equations governing thestructure action under permanent and traffic live load are derived. A parameter of"Critical Under-Deck Eccentricity" which reflects important structural characteristicshas been proposed for the first time.2) With respect to the geometric parameters including under-deck eccentricity,eccentricity ratio, along with the structural factors such as number of cable-strut unitsand supports, the preliminary investigation of the structural response under traffic liveload is conducted. The results indicate that the girder force and cable force incrementare smaller than the corresponding traditional cable-stayed bridge, and the proposedstructure shows better dynamic characteristics, whereas a few of local disadvantageshave occurred as well. With the increase of support, the insufficiencies have beencompensated and the advantages have been more fully manifested, which indicates that the innovative structure is more adaptive for denser cable arrangement scheme.3) A more detailed parametric analysis has been conducted for the Extradosed andIntradosed Cable-Stayed Bridges with denser cable arrangement, the results show thatthe proposed bridge with lower pylon and moderate under-deck eccentricity canimprove the structural behavior, and a proper matching of cable-girder stiffness issuggested to make the girder in a reasonable stress state. Compared to the conventionalcable-stayed bridge, the proposed bridge well designed is proved to achieve the betterglobal structural performance and local mechanical behavior of the girder deck,especially for longer spans, in which the girder deck can be very slender and the pylonheight still remains small. Some useful guidelines are also given for designing theproposed bridge.4) Further analyses have been expanded for the Extradosed and IntradosedCable-Stayed Bridges with different pylon-girder-pier connections. Compared with thecorresponding traditional cable-stayed bridge, the proposed structure shows better staticand dynamic characteristics under traffic live load, earthquake as well as temperatureeffects, and different benefits occur in different pylon-girder-pier connections. Thusmore comprehensive summary of applicable conditions of this structure has been drawn,which can be useful to the actual design.5) A re-design of an actual cable-stayed bridge has been done by using theExtradosed and Intradosed Cable-Stayed configuration, the superior mechanicalproperties and good economy of the proposed structure have been proved through thispractical project.