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Multi-storeys more complex than bridges, says report

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MULTI-STOREY car parks are 'unique' civil engineering structures with more complex loading than bridges, according to a new government backed research report launched this week.

Such structures should never be treated as buildings, and all key inspections and assessments require the combined skills of structural engineers and materials experts, the report warns. It concludes that good management of surface water drainage is the key to long term durability.

The research was jointly funded by the Office of the Deputy Prime Minister, the ICE and industry under the Partners in Innovation programme, and carried out by consultant Mott MacDonald. The report is intended to enhance the design recommendations drawn up by the Institution of Structural Engineers and the guidance on inspection and maintenance currently under preparation by the ICE.

Mott MacDonald project manager Neil Henderson said the report's findings were based on inspections carried out on more than 200 of the UK's 4,500 or so multi-storey car parks .

The oldest looked at dated back to 1948, while the most recent opened last year, he said.

'Two things were obvious.

Structures that had good drainage, were well maintained and regularly washed down had performed well. And joint detailing was critical.'

Henderson added that problems, especially with structures designed and erected in the late 1960s and early 1970s, usually stemmed from a failure to realise how complex the loadings were that multi-storey car parks were expected to accommodate - and how bad the exposure conditions actually were.

Carbon fibre rods strengthen car park

UNDERSTRENGTH CANTILEVERS on a 1960s multi-storey concrete car park in Bristol are being stiffened with carbon fibre rods, the first time the method has been used in the UK.

Developed in France and marketed in the UK by MBT Feb, the technique involves cutting 20mm by 20mm chases in the top of the 205mm deep slab and the insertion of 7.5mm diameter carbon fibre rods. Six of the car park's 11 levels of 3.2m long cantilevers are being strengthened in the operation, which is designed by Tony Gee & Partners.

'Surveys had shown that the main steel in the cantilevers was up to 80mm below the surface, seriously reducing flexural strength, ' said Tony Gee partner Neil Farmer. He added that the new system, dubbed 'near surface mounted reinforcement', had been chosen over the more conventional alternative of bonding on pultruded carbon fibre reinforced plastic (CFRP) strips for three main reasons.

'First, surface bonded reinforcement would be vulnerable to damage, ' Farmer explained. 'Then there's the inevitable laitence on top of the slab, which would make getting a good bond more difficult. So would the fact that the top surface of slabs is always rougher than the soffits.'

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