Paris match

?The car manufacturer left the 74ha (183 acre) Seguin Island-Rives de Seine site in 1992 for larger premises elsewhere, and it was left largely derelict until a master plan was approved in 2004. In the meantime, Renault decontaminated the ground and sold individual parcels of land to developers. The site is controlled by public-private consortium SAEM Val de Seine Ameneagement. The consortium is responsible for managing site construction and tendering consulting engineers. It will be directly responsible for building a 7ha park and facilities including a school and a three-level underground car park.

A 35ha middle section, known as the trapeze, is being built in two phases. In the west section, work on 31 buildings in nine lots has already begun, and they are scheduled for completion in March or April 2010. The east section work, on which building plans are not yet final, is expected to be finished by 2014. Some 900 of 1,000 apartments have already been sold for prices around EUR 6,000 per sq m, most of which have not yet even been built.

By the end of the year, there will be 25 tower cranes at work simultaneously on three of four lots on a plot measuring 240m by 290m. When visited in July, there were six tower cranes building six towers in just the first lot, two cranes working on a car park, two cranes on a residential block and two more on a riverside block. The cranes were a mixture of six flat-top Potains and five saddle-jib and one flat-top Liebherr, supplied or subcontracted by individual contractors. Crane rental companies include Arcomet, SOFRAL, and Matebat, and construction subcontractors include Eiffage Construction and Brézillon. The cranes support concrete pouring by lifting shuttering, frameworks, concrete skips and other loads.

Most of the 31 tower blocks were limited to 10 storeys high—about 40m—by local ordinances, with between two to four storeys of subterranean parking, so there are no climbing tower cranes. Each of the contractors specialise on certain types of building: Icade for housing, Nexity and Vinci for housing and offices, and Hines for offices. Sometimes, says Christophe Picard, coordinating engineer of CICAD Consultants, three builders are working on the same building. The site is 50% residential, 30% offices and 20% commercial and public space. CICAD won a four-year tendered contract for engineering consultancy in 2004.

To deal with the problems of overlap, Picard developed a tower crane coordination document that contractors had to sign up to.

CICAD signed off on each contractor's tower crane plan, checking whether contractors had taken into account wind turbulence caused by nearby tower blocks interfering with the prevailing west to east breezes (maximum wind speed on the site is 20m/s). It also signed off on their plans for tower crane heights, positions, heights under hook, elevation plans of the crane with final building height and proximity to nearby cranes. It checked that they met minimum French clearances of 2m. Once the plan was fixed, CICAD allowed the contractors to erect their cranes.

In addition, CICAD required contractors to fit an anticollision system from France-based manufacturer SMIE. Anticollision systems use position sensors and computer hardware and software to prevent tower crane jibs hitting each other, or each other's ropes. They are required by law in France for job sites with more than one tower crane. But CICAD went a step further. It standardised all anticollision systems on the site, for seven years, with French firm SMIE. All of the contractors are required to work direct with SMIE to fit SMIE AC 243 anticollision systems, and use SMIE exclusively for service. This standardization simplifies fault diagnosis, saving time and money, Picard says. "We wanted to find a company who can manage French tower cranes and foreign tower cranes," he said.

It also demanded that SMIE maximise the number of cranes on a radio frequency, to minimise radio frequency use. For this job, SMIE increased the number of tower cranes on a single network from 9 to 14 with special software designed for large worksites. SMIE engineer Lionel Loisy, who manages the site, said that the contractors have followed French preference for saddle-jib and flat-top towers instead of luffing-jib cranes.

Still a single network will not be enough for all the cranes, so the company is planning to run two over the most congested part of the site. That means that one centrally-positioned crane will run in two networks. When its jib slews to the left, it will be governed by one anticollision network; when it slews to the right, it will be controlled by the other. To accomplish this, the crane runs equipped with two complete sets of position and angle sensors. All four contractors had to dip into their pockets to pay for this extra system.

In addition, CICAD required contractors with tower cranes that overlapped to sign an agreement to make sure that tower cranes could be used during all of the site's working day, 7am to 8pm. If, for example, an operator driving a tower crane underneath another finishes work at 4pm, and sets the crane jib to swing freely in the wind, the tower crane above cannot work for the rest of the day. To deal with this, CICAD requires contractors to make legally-binding arrangements with each other to solve this problem, for example to agree to employ another crane operator to fill the extra time.

CICAD runs a control console at its head offices, but only examines recorded data in the event of problems. So far the only problem was a single case of interference, which was reported at 7am and repaired by 12pm that day. "The contractors are major companies," Picard says. "If there are problems, they will complain loudly. The planning penalties are very heavy; it is a must for them to work quickly and safely."

Other parcels on the site include a Norman Foster Partners-designed office block, occupied in September 2007 by Beaufour Ibsen Pharma; a high-profile 11ha island where the American University of Paris is planned, among other projects; and architect Jean Nouvel's 21-storey 90m-high tower, which features six storeys of car parks underneath and a multiple-storey glazed cupola at the top.??