The need for speed

The Concrete Structures for the Cuatro Torres in the Spanish capital of Madrid are rising towards the sky on a weekly basis and will soon become Spain's tallest buildings. The development's three towers are all being built under separate contracts but they all have one thing in common - the formwork solution that is behind the rapid progress.

Torre Repsol - the tallest of the three towers at 250 m - was designed by UK-based architect Norman Foster and is being built by a joint venture of FCC and Ferrovial's Dragados subsidiary. The tower features two externally positioned cores and is being constructed using Peri's ACS (Automatic Climbing System) formwork and Vario GT 24 girder wall formwork.

The other two towers, the 223 m Torre Espacio and 249 m Torre de Cristal are being built by OHL and Dragados, respectively, and are also being constructed using slight variations of the same formwork system. Work on all three structures started in 2003 and are scheduled to be completed next year, so ensuring maximum productivity and achieving the planned weekly floor construction cycle was essential.

According to Peri, the ACS system was selected for the project because the self climbing design meant that work would be able to meet the tight construction deadlines. The system uses hydraulic jacks to raise the formwork into position for the next cycle of construction, rather than using the conventional method of relying on cranes to lift the formwork.

Using cranes to lift the formwork is not only weather dependent but the concrete construction also has to fit into the crane schedule, which can result in delays. Peri's ACS system's ability to self climb allowed work to progress without the need for crane time, so the work could progress on time no matter what the weather or the crane's programme.

But while the scale of work underway at Cuatro Torres is significant, the rate of progress is not exceptional, and is being repeated on projects right across Europe.

Another project which is benefiting from a self climbing formwork solution is construction of the Tour 1 Tower in Paris, France by main contractor Bouygues. The 180 m tall tower is being advanced by almost 4 m every four days, without use of a crane, by using the SCF (Self Climbing Formwork) system developed by Hünnebeck.

The system is being used to cast the 22 m square central core for the semi-elliptical building in Paris's La Defense district. The Hünnebeck system is formed by nine platforms, each supported by a single 13,6 tonne bearing capacity bracket, instead of the usual two.

“The design of the building with a central 25 m corridor, made the single bracket solution possible and has helped to reduce the complexity of the system, said Hünnebeck applications specialist Thomas Hofmann. “Despite only being supported at one point, the platforms are very stable and give the operators up 8 m² of working space.

The platforms, which have a combined weight of over 450 tonnes, are moved up to the next casting level in one go by five hydraulic jacks - two on the outside and three on the inside. According to Mr Hofmann, the raising operation can be completed in less than 30 minutes.

Protecting People

Most of the major formwork manufacturers have self climbing systems in their product range. But while the systems mean that the lifting cycle is unaffected by the weather, the height of construction on many schemes othen still leaves the workers open to the elements.

Doka and Peri have both launched products which focus on improving working conditions on high rise developments, which also provide protection for workers both above and below the formwork level.

Doka's Windshield system, which can be used with its self climbing technology or conventionally ‘jumped' by crane, provides edge protection and encloses the work area to project against wind and other adverse weather conditions. According to Doka, use of the Windshield system not only reduces downtime due to poor weather but, because the operatives have a more secure working environment, the system can actually help speed up work on site.

Windshield is currently being put to the test on construction of two towers for the Tornimäe residential and hotel development in Tallin, Estonia. The joint venture contractors, Merko and Kontek, had just 11 months to complete the concrete structures for the 112 m tall towers. This meant working through last winter and no room for delays.

“The system enabled us to safely carry out the floor slab forming operations and speed up the construction sequence to complete the work on time in July, said Merko head of concrete level along with the other formwork elements. A self climbing version of the system is also made its debut in Chicago when main contractor James McHugh started work on the Trump Tower in March.

While the latest formwork systems are helping to improve safety at the construction face, efforts are also being made to improve temporary edge protection on completed floor slabs below.

“Introduction of the new European edge protection standard EN13374 in 2004 means that the industry has become more focused on the need to improve safety, said Combisafe European sales director Gary Taylor. “The UK is ahead of the rest of Europe in embracing the standard but Germany, France, Spain, and the Benelux and Nordic countries are becoming much stronger on enforcing it.

According to Mr Taylor, scaffolding used to be the main way of providing edge protection but the number of contractors using purpose made equipment is increasing. “Combisafe is a range of products, which can work with any formwork solution, which make fitting edge protection quicker, easier and safer than the conventional scaffolding approach, he said.