Mor Temor

 2.9   Norway Floating Bridge

                                                                 Back to Index

Norway is a mountainous country with a long coastline and many fjords. Fjords provide a beautiful landscape, but pose barriers to building bridges, owing to their great depth. Since the development of oil wells in the North Sea, the Norwegians have been leading in the field of offshore structures. The expertise and experience on the design of offshore structures have been applied for innovative floating bridges.

In 1992, Bergsoysund Bridge was completed at Bergsoyfjord near Kristiansund at a sea depth of 320 m. The bridge, 845m long in total, is horizontally curved with the radius of curvature of 1300m and rests on seven concrete pontoon foundations with a steel pipe truss superstructure. This resulted in significantly improved resistance to the rolling motion while the water current and waves were not hindered.

The use of steel members in the superstructure is also very effective since it acts as either an arch rib, that is structurally much stiffer than a girder of the same cross-section when the current is coming from its convex side, or as a similarly effective catenary cable, even when the current is reversed. Through this arch or catenary action, the hydraulic loads are found to be effectively and predominantly transformed into axial member forces in the superstructure and reaction forces at each of the ends where the floating part is only connected by a flexible rod to an abutment on the land, resulting in a construction method that does not involve excavation of the seabed. The flexible rod is designed so as torsional moment, shearing forces and the axial force at both ends are transferred and at the same time appropriate flexibility is provided enabling absorption of the relative vertical displacement due to tidal variation.

In 1994, a second bridge, Nordhordland Bridge, was completed at a sea depth of 500m at Salhus near Bergen. In order to provide the bridge with navigation channel, a cable-stayed bridge is connected with the 1246-m-long floating part. The length, navigation width and the clearance of the cable-stayed bridge are 350, 50 and 32 m, respectively. The basic design concepts of this bridge remain the same as Bergsoysund Bridge and it is similarly horizontally curved but with some differences, such as a minimum radius of curvature of 1700 m, a superstructure of steel box girders and the use of flexible plates instead of flexible rods for connecting the floating part to the abutments at both ends. The flexible plates transmit torsional moment, shearing forces and axial force and provides the flexibility to absorb vertical displacements caused by tidal changes. Figs. 17, 17.1 and 18 show the Bergsoysund Bridge and the Nordhordland Bridge, respectively (Watanabe, 2003).

 Fig. 17 Bergsoysund bridge.

Fig. 17.1 Floating concrete-pontoon-supported for Bergsoysund bridge, during construction in the dry dock. 

Fig. 18 Nordhordland bridge.

Arch. Mor Temor