AN ULTRA slim bridge deck was the key element which last week won the design competition for Hong Kong's new Tsing Lung suspension bridge project.
Maunsell Hong Kong will produce detailed designs for the £650M structure, for which construction will begin in 2002. Tsing Lung will be the world's third-longest span when completed in 2007.
The design's so-called Generation Three deck structure could halve the depth of the steel box deck on the 1,418m main span to about 2.5m, crucially reducing deck weight.
Hong Kong Highways Department engineer and design competition committee chairman John Chai told NCE: 'That could be critical for the bridge because of severe constraints on its height. The bridge will have a span-to-sag ratio of one to 15 compared to a normal one to ten.'
The Hong Kong Highways Department is competition sponsor and the client for the project. Very short main towers are required because the bridge lies on the flight path out of the new Hong Kong International airport on the north side of Lantau island. The bridge will connect Hong Kong's second biggest island to the New Territories across the busy Ma Wan shipping channel.
'One tower must be just 169m high and the other 178m,' said Chai. This compares to 206m for the towers on the Tsing Ma suspension bridge nearby, although that has a shorter span of 1377m.
Maunsell deputy project leader Charlton Wong said the G3 deck design was being developed by the firm's two subcontractors, Japan's Chodai and Brown Beech Associates of the UK.
Chodai was consultant for the 1,990m span world record Akashi bridge and Dr William Brown of Brown Beech is well known for work on the second Bosporus Bridge in Turkey and for bridges in Italy. Brown first proposed the new deck design for the 3.3km span across the Messina Straits to Sicily.
The deck proposal will go through a series of wind tunnel tests to prove it can resist Hong Kong's typhoon force winds.
Meanwhile, the Highway Department also this week announced 22 first- stage proposals from 16 consultant groups for the 1,000m span bridge across the entrance to the Kwai Chung container ports.
The department believes a cable stay for the Stonecutters Bridge would make the best solution even though this would push technology beyond the 890m span limit so far achieved in Japan.