World record for Abu Dhabi's "Leaning Tower"

The United Arab Emirates of Dubai and Abu Dhabi are constantly vying with one another for record-breaking construction projects. Be it the tallest building, the largest artificial island, or its most luxurious hotel, all of these spectacular structures can be found in these two tiny emirates.

The latest iconic project to rise from the sands of Abu Dhabi is the spectacularly inclining Capital Gate Tower. Where the Leaning Tower of Pisa is "only" 4° out of the vertical, Capital Gate is inclined by a massive 18°, a 33% gradient that makes it twice as steep as the L'Alpe d'Huez stage of the Tour-de-France in the French Alps.

After its scheduled completion at the end of 2009, this extraordinary tower will merit an entry in the "Guinness Book of Records", a distinction that it is likely to retain for years to come. No wonder construction of the tower, which was designed by RMJM Architects, is testing the limits of what is technically feasible.

Elliptical layout

The 160 m high tower is being constructed on an extremely densely reinforced, 6000 m3 concrete podium, which in turn rests on 490 bored piles sunk 30 m into the ground. This huge volume of concrete was hauled to the site in 850 concrete mixing trucks in just 30 hours, and placed by five high-performance concrete pumps.

The central in-situ concrete core of the Capital Gate Tower is characterised by an elliptical layout and a large number of shafts, and is back-stayed into the podium. This transfers the horizontal loads resulting from the extreme inclination, and secures the tower against both wind loads and earthquakes.

For construction of the core, main contractor Al Habtoor Engineering is using 78 of Doka's SKE 50 automatic climbing formwork system and more than 1300 m² of its Top 50 large-area formwork.

Due to the increased concrete pressure resulting from the inclination of the shaft-walls, the Top 50 is reinforced with extra steel walings. In addition to this, the Top 50's corner zones are fitted with specially made steel walings and reinforced with a steel form-facing. This improvement results from the insights gained by Doka during its 2.5 year contract on the Burj Dubai.

Owing to the structures extreme incline the SKE 50 automatic climbers are safely guided up the structure core with the aid of suspension shoes specially developed for this task. In order to increase the load-bearing capacity of the climbing brackets and working platforms, while ensuring equally safe anchoring in the structure, thicker tie-rods are used.

With the climbing scaffolds firmly anchored in the concrete at all times, and the work-platforms railed-in on all sides, maximum workplace safety is ensured during all phases of forming. The formwork for the inside walls of the shafts is hung from a massive gallows construction, which is mounted on the climbing brackets so it can be raised with the entire climbing scaffold.

Weekly cycle

Using the SKE 50 means Al Habtoor's site crew can form, reinforce and pour one casting section every week. A total of 42 casting sections are being carried out with no change of form-facing. Thanks to the powerful hydraulic unit up to 30 climbing brackets can be raised at a time.

The SKE 50's platforms were supplied by Doka completely pre-assembled and were set up under the supervision of its experienced field service technician.