Growing structure
It is not only the height and design that make the Burj so special but also the demands relating to the concrete work (the quality of the concrete, the conveyors, and the formwork design), construction cranes, and fire protection.
Concrete work
In order to minimise the cross-sections of structural components, concrete of high compressive strength is used, this being achieved through the quality of the cement and the grain size of the aggregates. Expert mixing and conveying ensure that the concrete sets properly and develops its intended loadbearing strength after being placed. As the high daytime temperatures only permit delivery over short distances, concreting work is mostly done at night. Three mixing plants with a total capacity of 120 m3/h are installed next to the construction site. Risers, distributors, and flushing pipes lead to the placing positions, and all the lines are laid as construction work progresses.
The longest previous vertical delivery was 532 m, but in the construction of the Burj a height of more than 600 m needs to be covered. The concrete pumps have to build up extreme delivery pressures – with expectations of 200 bar. Special super-high-pressure pumps were developed for this purpose, with pipes, couplings, and seals that can withstand the pressure. Here too, the high daytime temperatures are a major factor, since the vertical concrete delivery pipes must be expected to expand substantially. What is more, high pressures can lead to the pipes clogging up, which will happen, for example, if the concrete demixes during pumping. To maintain the correct consistency, therefore, such additives as superplasticisers are mixed into the concrete.
The difficult construction and switching operations are carried out in accordance with strictest safety standards. Construction work is making rapid progress due to, among other things, a special self-climbing formwork. The teams are working in three shifts. All the members of these teams receive special training and attend safety meetings once a month. The slab-forming operations on the higher floors are safeguarded by a further special protection screen system, which climbs up separately as construction progresses. This prevents anyone from falling over the edges and protects the construction site areas down below from falling construction material. Also, in order to ensure that the structure core does not climb in waves, its progress upwards is monitored using state-of-the-art GPS surveying technology.
Construction cranes
Three luffing jib cranes climb up the structure core of the building within a guide frame. The advantage of this is that the machine platform has a short turning radius, which is all the more important as the diameter of the tower decreases. The cranes' deadweight and the forces and moments from the live load of construction work are transferred into the structure core. The greatest danger is that inadequately secured building loads could fall down. Material failure in the cranes is also conceivable. In view of the extraordinary demands of the Burj project, the construction machinery and equipment are insured separately from the CAR policy.
Fire protection
There have already been a few fires on the site of the Downtown Dubai project. For this reason, and due to the Burj's extreme height, fire protection is of particular significance.
The fire risk can be minimised above all by taking appropriate organisational measures. With 2,000 people working in three shifts, the correct equipment and strict observation of all the safety regulations are essential. This includes a strict smoking ban and special fire protection regulations for welding and cutting operations in the steel construction. Furthermore, combustible waste must always be removed from the construction site.
As far as technical fire protection is concerned, it is essential that a pressurised water supply line be raised as construction work progresses. This alone can ensure that if a fire does break out during construction, there will be sufficient quantities of fire water available at the necessary pressure. During construction, numerous lifts are already available for use so that the site can always be evacuated at short notice.