ALL LINKSPANS and ship to shore bridges at UK roll-on roll-off (ro-ro) ports will need to be reviewed following the introduction of a new British Standard, port engineers warned this week.
Nearly 13 years after six people were killed when a passenger walkway plunged 10m onto a pontoon at the Port of Ramsgate (NCE 22 September 1994), guidance on design of ship to shore bridges has finally been published.
The Ramsgate catastrophe was found to have been caused by fundamental design errors.
Unforeseen transverse rotational movement on hinges designed to allow vertical movement and resist shear caused a weld to fail.
The accident led to calls for guidance, but funding to enable drafting of a new British Standard was not secured from government until 2003.
BS 6349 Part 8 'Code of Practice for the design of Ro-Ro ramps, link spans and walkways' was launched by technical body PIANC at the ICE earlier this month. Chief among the new code's recommendations is that redundancy be introduced to link spans.
'Link spans are one of the few structures where people are supported permanently by the lifting equipment - whether that is winches or hydraulic cylinders, ' said Royal Haskoning associate director Steve Osborn, who led the BS committee.
'The only other type of structure where this is permitted is passenger lifts in multi-storey buildings, where regulations are very, very tight. Secondary support or failsafe brakes are mandatory. But in case of link spans there's been no requirement at all.
'The new standard states that if lifting equipment should fail there has to be a second load path to catch the load.' He said that over the last decade there has been broad consensus among designers on providing redundancy, but many older link spans do not have a secondary means of support.
'The standard isn't retrospective, but [port owners] will be reviewing their structures. All of the ro-ros need to be looked at - there'll be widespread nonconformities, ' confirmed Port of Dover head of mechanical and electrical services Chris Clewlow.
'People will need to weigh up the risk of collapse against the cost of bringing their link span into line with the new BS, ' he added.
Cass Hayward partner James Parsons said that in the past design standards for link span structures have been derived from highway bridge design codes, but that loadings are often far higher.
'The new standard draws attention to the fact that traffic tends to be segregated. All of the lorries embark or disembark the ship together, which leads to far higher loading of a link span than you'd normally get on a road bridge, ' he said.