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Draft standard ignores lessons of Ramsgate

PLANS FOR a new British Standard on maritime structures fail to address the lessons learned from the Ramsgate link span bridge disaster in 1994, a leading maritime engineer warned last week.

The draft standard ignores the need for an integrated structural and mechanical design approach to link spans, said Posford Haskoning associate Richard Marks.

In 1994, a walkway linking a ferry to the dockside at Ramsgate collapsed, killing six people (NCE 22 September 1994).

Marks raised his concerns about the latest draft of the maritime structures code for the design of roll on roll off (ro-ro) ramps and walkways at an Institution of Structural Engineers meeting last week.

'If existing link spans were designed in accordance with the new draft, a number of them are likely to be demonstrated to fail, ' he said.

A recent draft of the new Part 8 of BS6349 had a number of weaknesses, he added.

The code only calls for designers to accommodate 'typical' waves when working up plans for link spans, said Marks.

There would then be a risk that movement induced by an exceptionally large wave could cause a link span attached to a ship to fail.

Marks also said that the draft code assumes operators will not adjust link spans under live loadings, when in fact this is common practice.

Bearing failure and poor design were blamed for the accident at Ramsgate. Investigations following this incident led to a new part to be included in the British Standard.

Posford Haskoning believes that safe ro-ro bridge design relies on the use of simple, robust components that are easy to inspect, maintain and repair, said Marks.

He said proprietary bearings are often over-complicated and are refined in accordance with commercial needs, resulting in lower safety margins. Poorly drafted project briefs were also to blame for badly designed link spans, as the full scope was often too vague.

BS6349 committee chairman Paul Lacey said that the standard was still at an early drafting stage and that the copy seen by Marks was not officially out for consultation.

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