High-rise buildings, by the sheer nature of their dimensions, can pose tremendous problems. Of the essence are such matters as time, efficiency, economy and safety. If you can reduce the time taken by cranes by having self-climbing formwork and special platforms and provide the required concrete surface, some of the bother about this kind of construction could be eliminated.

Now German formwork specialist Peri is proving once again it has the technique to meet the grittiest challenges. The site is the Kingdom Trade Centre, a 34-storey, 300-metre edifice piercing the Riyadh skyline.

'It was clear for the client that with this difficult project the available crane capacity would be decisive and that successful completion would be dependent on the formwork concept,'says Peri's construction manager Alberto Duronio.

'Peri presented a combination of two climbing systems on the 34-storey core which reduced the available crane capacity and, at the same time, kept the budget for the whole formwork costs within reason,' he says.

Elaborating on how the system worked for the project, he says: 'A total of 432 sq m of Vario wall formwork climbed independently of the crane on 22 ACS-R platforms on the outside of the core. The internal walls were formed with Vario on CB 240 brackets. Formwork and climbing scaffolds formed a single unit that could be moved by the crane, thus saving time. The Z-shaped special steel beams made the construction of the enormous edge beams easy and that cone-shaped beams were used for easy striking and saving concrete.

'After removing the internal formwork, the external ACS units are climbed hydraulically to the next lift. At the same time Vario served as perimeter formwork for concreting the slab.'

'We could drastically reduce the onerous crane times of this gigantic construction site with ACS. Working with the self-climbing formwork is very easy, safe and exact.'

'For the subsequent floor slabs, two Uniportal table sizes - 5.00 by 3.00 m and 5.40 by 2.70 m - and optimum beam tables for the building - principally 3.30 by 2.10 m - completed the total economical concept. The team at the site was easily able to complete the building, floor to floor, in a regular four-day cycle. The core grew ahead of the following slabs by two storeys,'he says.

Peri estimates that with 60 slab and 88 beam tables about 1,660 sq m of floor area was formed each time.

At the end, it was clear that Uniportal tables on Multiprop props provided short formwork cycle times and excellent concrete surfaces, despite varying slab heights (4.10-6.25m) and radiallly-arranged beams, Duronio says.

'Well-considered working sequences provided a perfect combination of various formwork systems. Cleaning and reinforcing work can be very easily carried out in the protection of the retracted Vario formwork,'he adds.

The Kingdom Trade Centre, which is being built for the Kingdom Holding Company, by El Seif Engineering, is scheduled for completion later this year.