STONECUTTERS BRIDGE designer Arup this week revealed that it had moved even further away from the original design chosen by the Hong Kong Highways Department.
Arup director and bridge team leader Naeem Hussain confirmed that the detail design team had abandoned Pont de Normandie-style integral joints between the twin box girder deck and the record breaking 290m high single leg towers.
Arup has already switched to a form of cable stay which the original designers had rejected on the grounds of increased wind loadings.
With a main span of 1,018m, Stonecutters Bridge will be the longest cable stay crossing in the world when it opens in 2008.
Integral joints had been a key feature of the first stage competition winning design drawn up by a Halcrow/Flint & Neill team with architect Dissing + Weitling and the Shanghai Municipal Engineering Design Institute (NCE 14 December 2000).
But Arup has decided to use transverse bearings and longitudinal hydraulic buffers.
'This will allow the deck to float past the towers and give a more pleasing visual appearance, ' said Hussain.
Reasons for the change include the difficulty of analysing the complex stresses in the 11m wide joint and potential construction problems associated with such a heavily reinforced insitu concrete element.
Flint & Neill partner and original design team member Ian Firth said it was a 'shame' that the concept had been abandoned.
'We went for an integral design because it greatly simplifies maintenance and eliminates bearing movement problems, ' he said.
One possible knock-on effect of the change is greater bending moments in the circular cross section towers above deck level.
These are also being modified as the result of wind tunnel testing at the Danish Maritime Institute's facility in Copenhagen.
Earlier 1:100 tests on the original tower design had revealed vibration problems due to vortex shedding during high winds.
Although Arup continues to respect the original tower shape, Hussain confirmed that internal proportions have been modified to bring the frequency and amplitude of vortex-induced vibrations back to acceptable limits.
He also revealed that contractors will be allowed to lift main span steel deck sections into place from the Rambler Channel.
The original design team had been briefed to minimise disruption to shipping in the congested waterway, which gives access to one of the busiest container ports in the world.
They chose to launch the main deck from the massive approach viaducts, but the original restrictions no longer apply.
INFOPLUS www. hyd. gov. uk