Extradosed bridges are often described as a cross of a conventional prestressed concrete bridge a+G32nd a traditional cable-stayed bridge because most extradosed bridges built combine a prestressed concrete superstructure with stay-cable technologies. However, this simple definition does not capture the various possible structural systems and different materials that can be found and used for extradosed bridges. Extradosed bridge technology is much more than a prestressed concrete girder with external tendons.
The Deh Cho Bridge in the Northwest Territories and the Canal Lachine Bridge in Montréal are two Canadian extradosed bridges featuring steel superstructures with slender composite concrete decks using full-depth precast panels. Although both bridges are very different, they share one important constraint which governed the design of their superstructures: Both bridges are located in regions with prolonged extreme cold winter periods. Below zero temperature extending over a longer period can be a major hindrance when erecting long bridges with conventional concrete superstructures. On the contrary, steel superstructures are light and can be quickly erected, even at far below zero temperatures without heating and hording given that field welding is avoided.
To avoid delays along the critical path in the erection of major superstructures in extreme cold temperature zones, designers should consider erection schemes which make best use of short warm weather periods and reduce negative impacts related to harsh weather conditions as best as possible. To achieve this design objective, it is recommended that proven construction schemes and technologies are investigated in the early design phase of the superstructure design before superstructure type, cross sections, and materials are selected. This holistic approach goes far beyond what commonly is described as Accelerated Bridge Construction (ABC) because the goal here is a tailored superstructure design for the specific location of the structure including the preferences of fabricator and contractor.
The paper will present the specific design features and construction methods selected for the Deh Cho Bridge and the Canal Lachine Bridge. Structural details and achieved synergy effects by combining superstructure design and erection engineering will be discussed. Further, the advantages of modern light-weight construction principles over traditional girder superstructure types will be emphasized to demonstrate their advantages when building bridges in seismic zones.
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