Kunstig sjøbunn for lange flytebroer

A feasibility study, "Ferry-free coastal route E39", carried out by the Norwegian Public Roads Administration (NPRA) has investigated the potential a ferry-free coastal route will represent for trade and industry and thus for employment and settlement in the region. The study concluded that a ferry-free coastal route, with permanent fjord crossings, is preferred based on increasing the above measures. For some of the deep fjord crossings, floating bridges may be more cost effective than traditional air spanned bridges. Although, compared to air spanned bridges, long span floating bridges require side moorings. Such a floating crossing is suggested by REINERTSEN AS together with their partners. The crossing consists of a floating bridge with a subme rged floating tunnel (SFT) at mid span, latter to allow for ship traffic in and out of the fjord. In conjunction with the crossing, a new mooring concept for floating bridges with no direct seabed mooring is suggested. This "artificial seabed", consists o f pre-tensioned pipes across the fjord at a water depth of 30 m, moored to each of the shores. The proposed concept takes advantage of proved mooring technology from the offshore oil and gas industry, where mooring of floating platforms were found econ omically advantageous as the deep water fields were explored. Floating structures may be cost effective. However, wave, current and wind induced motions have to be dealt with to ensure structural integrity, safety and comfort. The project has run physical experiments to study the behaviour wave, current and wind induced motions will have on cross sections relevant for the proposed fjord crossing. Also work packages on the ship barrier (both in aluminium and steel) and marine operations and installation are looked at. These aspects are important for the concept and are not presently documented in existing guidelines and regulations. Recently a HAZID (hazard identification) has been carried out. Results did not give any direct show-stoppers. Still; further detailed analysis of certain elements, as well as risk evaluations with respect to load combinations were flagged as further works. Publications/links: Norwegian Public Roads Administration: Highway 39 - a national, regional and local artery Norwegian Public Roads Administration: film about the E39 project Strait crossings. Morten Bjerkås og Tore H. Søreide, REINERTSEN: Mooring concept for deep water crossings (s. 409) Fluid induced motions of multiple cylinders, pipe bundles and pentago nal cross-sections.pdf

Prosjektet skal utvikle og dokumentere en ny løsning for forankring av lange flytebroer. Arbeidet skal gjennomføre forsknings og utviklingsaktivitet for bringe et nytt konsept for forankring av flytende pontonger i forbindelse med brubygging. I tilfeller der store vanndyp skal krysses vet en av erafring at klassisk vertikal stagforankring til sjøbunnen kan være utfordrende og usikkert. Det er i denne sammenhengen lansert en ide som går ut på horisontale stålrør i hele fjordspennet som forankringspunkt for en veibane på flytende pontonger. Ideen er basert på norsk plattformteknologi utviklet gjennom de siste 20 år på norsk og senere internasjonal sokkel. Ved å benytte forspente stålrør i neddykket tilstand vil en kunne forankre den kritiske vertikale beveg elsen av veibanen uten å gå ned til sjøbunnen. Prosjektet har som hovedmålsetning å oppnå en teknisk godkjenning hos de norske veimyndighetene for deretter å kunne selge lisenser direkte til byggherrer eller delta i anbudskonkurranser for total leveranse. Det er gjort foreløpige sammenligninger av kostnader som antyder at et slikt konsept kan representere en kostnadsreduksjon på ca 40 % i forhold til de lengste bruspenn som er konstruert i Norge pr idag.