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Reinforcing rolls

CONCRETE

A new German-developed slab reinforcement system is on site in London. Andrew Mylius reports. Pictures by David Jones.

Ballast Wiltier site manager Jim Mackay says his £6.5M seven storey shell and core contract, close to Tower Bridge, is technically straightforward - apart from tight access.

As subcontractor to main contractor Norwest Holst, Ballast Wiltier started construction of the 124 flats for client Fairview Homes in March. Progress since then has been speeded by one of the first UK uses of a 'carpet' slab reinforcement system that, MacKay reckons, will save eight weeks on the construction programme compared with conventional set-out and tie as you go reinforcement.

Currently around 750m2 of carpet is being laid in a day - against the four or five days Ballast Wiltier calculate it would take to fix the same area of conventional reinforcement. A total of 15,000m2 of reinforcement carpet will be supplied under a £100,000 contract by Liverpool-based Hy-Ten Reinforcement .

To produce the bespoke carpets, Hy-Ten feeds CAD information from structural engineer Waterman into a computer-controlled production system that turns out prefabricated reinforcement with the kind of precision found on automotive production lines. Once a section is complete it is rolled up, delivered to site and lifted into position. With a deft kick the carpet can be unrolled by a couple of workers on to conventional continuous chairs or spacers.

Hy-Ten holds the licence for the system from German company Bamtec, which developed the design-manufacture package with software firm Nemetschek and machinery supplier Hundegger in 1994. Hy-Ten set up its first Bamtec plant last year and raced to keep up as demand has snow-balled. It will set up a second plant this year and plans to have four in operation within three years.

The system is approved by CARES, the certification authority for reinforcing steels, and complies to BS8110 as well as Eurocode II.

In principle the Bamtec system can deliver just-in-time, says Hy-Ten director Paul Butler. Consultants and contractors are starting to use Bamtec software to produce reinforcement schedules which can be e-mailed to the factory computer in Liverpool. Using this information the factory spot-welds reinforcing bars of specified diameters to steel tape, indexed through the machine to ensure each bar is fixed exactly where specified.

'It should make sure the stuff hits site in the right quantities and in the right dimensions,' says Butler.

Bamtec software uses finite element analysis to map the loading contours for slabs. It then calculates reinforcement for base-, mid- and top-layers separately, automatically identifying the required diameter, position, length and spacing of every bar.

Butler claims Bamtec can improve structural efficiency and cut waste resulting from over specification and over-ordering by as much as 25%.

Carpets of up to 15m wide and 20m long, and weighing 1.5t can be produced in the Bamtec factory. It can make up carpets containing bars from 8mm to 32mm diameter, spaced at centres from 25mm to 600mm. The controlled environment of the factory meanwhile assures levels of accuracy and quality control difficult to achieve on site, says Butler. 'And there are no delays caused by bad weather.'

MacKay meanwhile testifies the system's reliability cuts down on on- site inspection required. Because each carpet has a precise location the system also reduces opportunities for confusion and the need for correction.

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