ORIGINAL PLANS to minimise traffic disruption during the replacement of a key roadbridge in Suffolk have been heavily modified after delays to starting the contract, Suffolk County Council confirmed this week.
An ingenious temporary bridge design developed by structural engineer Arup has now been simplified in conjunction with contractor Costain to save construction time.
The design concept was said to be a key factor in a joint Arup/Brookes Stacey Randall team winning the first ever Royal Institute of British Architectssponsored design competition for a roadbridge (NCE 10 August 2000).
Ballingdon Bridge is just south of the busy market town of Sudbury, and the original design was intended to keep two lanes of traffic flowing across the River Stour for as much of the original 62 week contract as possible while the 90 year old concrete structure was replaced.
Listed buildings close up to three corners of the bridge made conventional solutions impossible. The planned temporary structure would have squeezed two lanes of traffic above the outer two thirds of each side of the bridge in turn while the other third was demolished and replaced with precast units Half the width of the temporary bridge would then have been removed to allow for the centre section to be worked on.
But now a much simpler design which can only take one lane of traffic at a time has been adopted. Suffolk County Council bridge improvements and maintenance manager Nigel Burrows said the design had turned out to have several advantages.
'A one lane solution gives more working space and allows Costain to complete the works significantly faster, ' Burrows said. 'And it's slightly cheaper as well.'
Arup associate Stuart Smith denied the abandonment of the original temporary bridge concept would lead to greater congestion in Sudbury's narrow streets. 'In fact the total period of single lane working will be the same, at 32 weeks. But this way we've cut 10 weeks out of the original 62 week programme.'
Saving time on the contract became imperative after delays in purchasing land near the site and pressure from residents to postpone the bridge works until after major sewerage works were completed put back the original start date by many months (NCE 15 March 2001).