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The contracting JV, consisting of Mohammed Abdulmohsin Al-Kharafi & Sons W.L.L. and Philipp Holzmann, started work on the new athletics stadium in the summer of 2004, and it is scheduled to open in December 2006. The structure shell will require the casting of 52 hollow wall piers from in-situ concrete.
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For the stepped beams, which cantilever out by as much as 50 m, Doka supplied a formwork solution that needs no falsework support.
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Stepped beams cantilever out as much as 50 m from the tops of the walls, rising to a height of 65 m. They carry the roof construction and the grandstands, and are stiffened in the horizontal by connecting cross- eams that are also made of reinforced concrete.
Climbing cantilever formwork for 65 m high stepped beams
The wall piers are being cast using 8 complete sets of formwork.These are made up of Top 50 large-area formwork on Climbing brackets 150 F. When it came to the inclined cantilevering stepped beams, the contracting JV were looking for an operator-friendly and wind-stable formwork solution. The Doka solution does away with the need for equipment-intensive, high-cost falsework supports for the up to 65 m high stepped beams. Instead, a special cantilever formwork was developed which can be “jumped” in a similar way to a climbing formwork. This permits huge savings in terms of falsework and labour costs.
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| Project engineer Adel Hamdy is responsible for ensuring that construction work progresses smoothly. He is taken good care of by Doka’s nearby Kuwait Branch. |
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Unlike a “classic” climbing formwork for vertical walls, however, this system has to sustain not only its own dead weight and the wind loads, but the weight of the fresh concrete as well, and transfer these loads into the previously cured section. In each set of formwork, elements of Top 50 large-area formwork are set up on 2 steel girders.
These steel girders are fixed in two climbing-shoes on the underside of the stepped beam. At the top, the whole system is backstayed with 10 m long tie-rods. The two 36-mm tie-rods, each with a failure load of 100 tonnes, begin at the outermost extremity of the formwork-set and end in the back-stay unit. This is made up of steel girders that are anchored in the concrete at the top of the stepped beam. These girders transfer the 70-tonne load of the fresh concrete into the previously finished section.
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The architects drew their inspiration for the stadium’s dramatic shape from traditional wooden merchant ships. The 250 m diameter stadium undulates elegantly upwards on two opposite sides.
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Owing to the very great heights involved, all the forming operations have to be ones that can be carried out in complete safety. For this reason, the Doka formwork solution comes with specially designed
working platforms. Each set of formwork has two side platforms for detaching or fixing the back-stays and form-ties, and for placing the concrete. Their staircase- like platform decking ensures safe working on these steeply inclined platforms. On the underside of the stepped beam, there are 3 different platform levels for operating the outside formwork, detaching or fixing the bottom back-stay point, and for relocating the suspension shoes. On the end face, there is one platform for operating the inside formwork, placing the reinforcement and for pouring.
Time-saving repositioning using climbing technology
Compared to supporting the stepped beam entirely with falsework, the climbing cantilever formwork results in very big savings of time and equipment. The stepped beams grow by one 5 m long segment every week. Up to a
length of 38 m, the usual type of reinforcement is sufficient. However, the biggest stepped beams – which have cantilever lengths of up to 50 m – need to be restressed. Suitable jacket tubes for the anchor blocks are installed at the same time as the reinforcement is placed. Project engineer Adel Hamdy has been looking after this formwork assignment right
from the outset: “On the stepped beams, we’ve been able to manage entirely without time-consuming falsework, thanks to the climbing formwork solution.
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| The climbing cantilever formwork saves the contracting JV from having to use large amounts of falsework, with the high labour costs this would involve. |
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| The formwork for the stepped beams is fixed in two climbingshoes on the underside of the beam. At the top, the system is secured with 10 m long tie-rods from the back-stay unit. This transfers the 70-tonne load of the fresh concrete into the previously finished section |
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