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Aesthetics rule in Oakland Bay suspension choice

AN INNOVATIVE single-tower asymmetric suspension bridge has been recommended for the £850M replacement eastern section of the San Francisco- Oakland Bay Bridge in California, despite costing £30M more than the cable stayed alternative.

Engineers on the Oakland-based Metropolitan Transport Authority's Engineering and Design Advisory Panel have backed the suspension design mainly on its looks, a California Department of Transportation (Caltrans) spokesman confirmed on this week.

'The suspension design gives a little better seismic performance as well, but it was chosen mainly because it blends in better with the suspension span on the western section of the bridge,' he said.

The bridge is part of a replacement for the existing crossing, built in 1936 and badly damaged in the 1989 earthquake. The new crossing will be more than 3.5km long and carry 10 lanes of traffic and, probably, also a cycle lane. Originally, an 'all-viaduct' solution costing less than £800M was proposed, but locals favoured the inclusion of a distinctive 'signature span'.

Caltrans says the bridge will add less than £100M to the cost. The main span of the suspension proposal is 395m, with a backspan of only 180m and a 160m high tower. Horizontal compression loads from the main cables will be taken by the bridge deck itself rather than being anchored to the bedrock. Caltrans believes that if built in this form it will be only the fourth major self-anchored suspension span in the world.

MTA makes its final recommendations to Caltrans on 24 June. Construction is expected to start in 2000 with completion four years later.

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