EXCESSIVE HOGGING caused by solar gain was this week blamed for the widespread concrete spalling on the troubled £200M Castlepoint shopping centre car park in Bournemouth.
The shopping centre reopened fully last week. It shut down on 30 November amid fears about the safety of the 3,000-space car park.
Trading losses are rumoured to total close to £1M a day for the four week period when all 40 stores including Sainsbury's, a B&Q, an Asda and a Marks & Spencer were closed.
Castlepoint general manager Peter Matthews told NCE: 'A temperature difference of 16°C has been measured between the upper and lower surfaces of the upper deck in summer.
'This has caused large movements at the ends of the 16m span deck planks, and widespread spalling of the supporting beams.' Reopening follows completion of a massive emergency propping operation below the twostorey car park's upper deck.
Main design and construct contractor Kier deployed up to 200 men working 24 hours a day seven days a week to install more than 2,000 steel props.
The centre has been re-opening in stages ever since 19 December (NCE 12 January).
The props sit on their own specially installed concrete pad foundations. They mostly support the ends of the long span precast concrete deck planks via steel I-beams installed each side of the precast concrete beams.
Longer span beams are also propped. Each group of props has been clad in marine ply boxes. Matthews said shoppers had reacted positively to the safety precautions.
'We've not had a single enquiry as to the safety of the car park, and no complaints.
It's been an amazing piece of work by Kier.' The decision to close the centre was inevitable once Castlepoint's structural engineer Arup warned that problems with the two year old structure had reached dangerous levels, said Matthews.
'There have been problems with spalling concrete almost since the centre opened, ' he added.
'The very first day I started work as manager in May 2005 the first big lump of concrete fell. This was a stalactite shaped fragment about 1m long and 150mm thick at its widest point.
'In fact this was almost the only case of spalling from the precast planks. All the rest has come from the beams.
'We closed the car park for 10 days, erected safety netting under every beam, and began propping as a precautionary measure near to where any big spalls occurred.' urrently the temporary support structures are 'soft propping' the carpark - they are in contact with the beams but are not taking any significant load.
A 1,000 bay ground level section below the centre's Sainsbury's store next to the car park, is unaffected by the same problem, as it is not exposed to sunlight and the main beams are steel.
Kier's structural engineer is Cameron Taylor, but the £6.1M precast contract was let on a design and construct basis to Amec subsidiary CV Buchan, which commissioned Hyder as structural engineer.
None of these firms are commenting on the problems.
Matthews told NCE: 'So far there has been no agreement on the cause of the spalling and Castlepoint has yet to receive any proposals for a permanent solution.
'Obviously the retailers who lost the busiest part of the trading year will be seeking compensation for their losses in due course.' Even shoppers arriving by bus or on foot were barred, as customer access to the shops is only via the carpark.