Huge Floating Steel Structure for Megafloat Completed
Construction of a massive floating steel structure measuring 359m long by 71m wide by 3m deep was recently completed at NKK's Tsu Works. The floating structure is one of six units being built by a group of shipbuilders and heavy-machinery manufacturers nationwide. The individual units will soon be towed to the northeastern breakwater off the port of Yokosuka in Tokyo Bay and assembled to form a 1km-long (Phase II) demonstration test model of a so-called Megafloat, designed for use as an offshore airport. The Megafloat research project is being undertaken by the Megafloat Technological Research Association, which was established in 1995 by 17 major steelmaking and shipbuilding companies, including NKK, with backing from the Transport Ministry and the Japan Foundation. The association is promoting development of technology required to support use of a Megafloat as an offshore airport, by conducting tests and proving its feasibility. The goal is to develop an ultra-large floating structure several kilometers in length and with an estimated lifespan of at least 100 years. As a first step, the association conducted Phase I tests during 1995-97 by constructing a floating model structure 300m long by 60m wide by 2m deep. The ¥7.6-billion, three-year tests verified design/analysis technology for floating structures, welding and joining technology under open sea conditions, installation methods for new corrosion-resistant materials using titanium-clad steel for splash zones to ensure a 100-year service life, and assurance systems for on-board facilities, with functions equivalent to land-based facilities. Environmental impact on the tidal flow and surrounding ecological systems was also assessed. Achieving initial development targets in hardware technology as well as in environmental assessment, the association has established a basic system technology for building a commercially viable Megafloat. Building on Phase I achievements, another three-year test program (Phase II) began in 1998, with the aim of proving the Megafloat's practical use as an airport. Under the ¥11.4-billion Phase II program, the six units will be joined offshore. Each ranges from 64m to 383m in length. The NKK-led joint venture was responsible for building the second-largest unit. Underwater joining work requiring extraordinarily high accuracy (tolerance of 1mm per 100m), will employ GPS (global positioning system) technology. Upon its completion, the floating model runway will measure 1km long and 60-121m wide (total area: 8.5 hectares). Extensive testing will begin in September and involve small- and medium-sized aircraft, which will make low passes as well as take-offs and landings. Aircraft instrumentation will also be monitored. The tests, which will aim to certify the safety and reliability of floating airports, will continue through the end of fiscal 2000. For Japan, an island nation with limited usable land space, the need for offshore utilization will continue to increase. Floating airports will be the optimum choice for meeting such requirements in view of the fact that they are more environmentally friendly than those built on reclaimed land. Airports are not the only possible use. As a highly earthquake-resistant structure, Megafloats are expected to serve a wide range of uses, including harbor terminals, leisure parks and emergency installations in the coming century.
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