Behaviour Analysis and Design of Extradosed Bridge

Abstract

Advancement in high strength materials and construction technologies along with the development of analysis, design software and value engineering has facilitated the growth of long-span bridges. Cable supported bridges have span varying from 250 m to 1100 m depending weather the bridge is cable-stayed, suspension, or extradosed bridges. Extradosed bridges are generally medium span bridges with a span range of 150 to 350m. It was invented in 1970, by Maithivat J. EXTRADOS means top fiber of an arch. In terms of bridge engineering, EXTRADOS means a bridge having external cables in the top fiber of deck along with internal prestressing. Extradosed bridge is an option between the cantilever constructed girder bridge and cable-stayed bridge. Extradosed bridges are more suitable where the height of pylon is restricted due to a nearby airport or deck depth is restricted due to moving vehicles under the bridge. In recent times, there is an increase in the construction of extradosed bridges. A case study of 40 bridges constructed in India and Japan has been carried out to understand the basic behavior and recent trends in extradosed bridges. A number of parameters like cable angle, deck depth, the height of the pylon, cable configuration, and much more appropriate configuration and combination of configuration are considered to achieve economy in construction. In the present work parametric study is carried out by varying stay cable profile, cable angle, location of cable, the height of the pylon, and construction methods. Two popular concepts for the design of extradosed bridges are one being stiff girder flexible pylon system and another being stiff tower flexible girder system. In the present study design is carried out by stiff girder and flexible pylon extradosed bridge having a span of 100 m +170 m +100 m. Gravity Loads are considered as per IRC - 6. The design of superstructure is carried out as per IRC -112, and stay cables are designed as per SETRA-2000 guidelines. Construction stage analysis and design are also carried out for the same bridge. Time taken for each construction stage is archived by construction scheduling of the bridge. A comparative study has been carried out to understand both the stay cable force finding methods which are Forward process analysis (FPA) and backward process analysis (BPA). From this study, we can conclude that both the methods give required data which can be used for design. In FPA we can model the effect of creep and shrinkage which can be note modeled in BPA so BPA gives 8% higher stay cable forces than FPA.