Prof. em. Torgeir Moan
Centre for Autonomous Operations and Systems (AMOS) and Department of Marine Technology, the Norwegian University of Science and Technology
Otto Nielsens veg 10, NO 7491 Trondheim, Norway
E-mail: torgeir.moan@ntnu.no
Abstract – To improve the efficiency of transport systems, bridges, submerged tunnels and subsea tunnels are introduced to replace ferries to cross straits. For wide and especially deep straits, floating bridges are attractive. The idea of floating bridges is not new. The modern floating bridges can be traced to the pontoon bridge design implemented in the 1940s A notable achievement was the 1988-m long Hood Canal Bridge built in 1963. More recent floating bridges built from 1990s include the two Norwegian floating bridges: 845-m long Bergsøysund and Nordhordaland Floating Bridges built in 1992 and 1994, respectively. Submerged floating tunnels have been considered as an option for strait crossings, especially wide crossing such as the Gibraltar and Messina straits and the Høgsfjord in Norway. So far submerged floating tunnels have not been built, while immersed tunnels has been used in many places, essentially in relatively shallow water. Currently, the Norwegian Public Roads Administration (NPRA) is assessing replacing ferries across 8 fjords by providing bridges, submerged tunnels or subsea rock tunnels on highway E-39 from Trondheim to Kristiansand. The width of the strait crossings is up to 6 kilometers and the water depth is up to 1300 m. Owing to the maximum slope of roadways, a subsea tunnel in rock will be very long and expensive. Also, due to the large free span of conventional suspension bridges their costs might be excessive. The NPRA is currently considering three alternative floating bridge concepts: Curved, End Anchored Floating Bridge or Straight, Side Anchored Floating Bridge by mooring system combined and Floating Suspension bridge with pylons supported by TLPs or spar floating bodies; and submerged tunnel type concepts. In this paper an overview of relevant concepts, characteristic behaviour and design criteria for serviceability and safety, with an emphasis on environmental loads and their dynamic load effects, as well as a brief account of the treatment of accidental loads and their effect.
Keywords – Buoyant bridges, design, functionality, safety.
Torgeir Moan is Professor em. of Marine Technology, NTNU; former Director of Centre of Ships and Ocean Structures at NTNU; the inaugural adjunct Keppel professor in offshore engineering at NUS; member of the Royal Inquiry Commission of the Alexander L. Kielland accident and other accident inquiries, as well as advisor to the industry, standardization organisations (e.g. Eurocode, ISO, PSA, Norsok, IEC) and universities. Professor Moan has carried out research as well as engineering design and analyses of oil and gas platforms, floating bridges as well as offshore wind turbines and FPSO ships. He has (co-)authored more than 700 journal and peer-reviewed conference publications, delivered more than 40 keynote lectures at major conferences, supervised more than 400 MSc and 80 PhD graduates and received several international awards, from e.g. MIT, ASME; the Offshore Energy Center Hall of Fame; Petroleum Safety Authority, several best paper awards and honorary professorships. He has been elected Fellow of three Academies in Norway and the Royal Academy of Engineering, UK.