Burj team keeps floor-cycle promise
Formwork is big business in the Middle East as project deadlines tighten and towers get higher. In a bid to maintain its three-day floor cycle, the Burj Dubai construction team is turning to a host of players in the formwork industry. Zoe Naylor reports on fast-track innovations by Doka and Meva.
When the Burj Dubai construction team announced that they would be completing one floor of the tower every three days, few people took them seriously. But one year into its three-year construction cycle and the Burj has already passed the 75-storey mark around halfway to its final height. A massive labourforce working 24 hours a day certainly helps to speed up the process, but another key factor that contributes to the swift floor cycle is the range of formwork systems that are being used on the tower.
The Burj Dubai's construction consortium of Samsung, Besix and Arabtec opted for the latest techniques in order to fast-track construction of the tower.
Austrian formwork giant Doka is supplying around 1,000 tonnes of its formwork material to the project.
This comprises SKE 100 self-climbing formwork for the tower's wall construction, and over 5,000m2 of Top 50 formwork, which is being lifted with 226 Doka automatic climbers in order to complete the 600m-high central core.
Re-use of the system is designed to exceed, what Doka claims will be, the final 160 levels of the tower.
While the Burj was originally scheduled to reach the 92-storey mark by the end of 2006, if it carries on at its current pace it is expected to be closer to 100 storeys, which means the project is running approximately 15-20 days ahead of schedule.
"It has been a learning curve," says Kyung-Jun Kim, project director, Samsung.
"At the start it took longer, but then we had to assemble the form systems and that took time. Similarly, there was more formwork handling required on the lower storeys compared with the upper storeys."
But as with anything, practice makes perfect: "We have speeded up as we have gained experience.
"The first time it took a week [to complete one level], then six days, then five, and then four days. Now we are down to three," adds Kim.
Doka's self-climbing system is being used for all centre core walls and wing core walls, rising ahead of the slab works.
In addition, the project is also using Doka self-climbing protection screens for complete exterior enclosure of slab works.
According to Kim, the Doka system was chosen because it met a range of criteria, from technical requirements through to safety issues: "It is a safe system and the Doka form assembly can accommodate all of the changes in the construction process such as the different wall thicknesses, which range from 600mm through 800mm to 1.3m.
"From the beginning, we sat down with the Doka engineers to consider in advance all of the changes. And there has been a very strong commitment from the Doka management to develop the best system that would achieve our goals. They have given us all kinds of support. The result is that we have all the solutions we need."
The cross-section architectural design of the Burj resembles a hymenocallis desert flower.
The structure has a base floor plate of 3,500m2; by the top floor this will have reduced to approximately 500m2
It has a three-section central core and three wings.
In order to keep the measurements of the structure down to a minimum and to bear increasing loads as the tower progresses, only concrete with high compressive strength is being used.
Delivering the concrete to these record heights means specially developed high-pressure pumps were designed to cope with extreme delivery pressure.
Putzmeister freestanding placing booms are positioned on 16m-high tubular columns and are anchored with girders to the working platform of the respective wall formwork.
The booms are then raised together with the formwork from one concreting section into the next.
An even larger stationary boom, with a 32m reach, is being used to concrete the core section.
The boom is positioned on a 20m-high tubular column and is supported and raised by Doka's self-climbing system.
While the central core of the tower is approaching the 80th level, the wings are between 10 and 15 floors behind.
In the three-day cycle, day one sees the pre-assembled cage installed inside the formwork, and inspected during day two.
Concrete is cast on the third day and after ten hours the form is struck and jacked up to the next floor.
Working on a project of this scale and speed means that safety must be of paramount concern throughout the construction process.
As a result, Doka's protective screens are being used for the first time in the region and were specified because of the high winds in the region.
"As the building goes higher, so the wind is stronger," says Kim.
"We have had to stop work when the wind speed exceeded 10m/sec. The screens provide protection and prevent falling objects, and enable the workers to work inside a safe area."
While Doka is supplying its self-climbing system for the centre and wing core walls, German firm Meva (in joint venture with UAE-based KHK Scaffolding) is supplying its MevaDec system for the slab formwork.
According to Meva, the floor slabs represent the biggest share of Burj Dubai's on-site concrete works and translates into a total surface of 224,808m² for 532 slabs on 153 floor levels, an area roughly the size of 33 football pitches.
"During construction the tower is divided into four areas for each level: Three wings and one central core," says Jens Lutzow-Rodenwoldt, Meva's Germany-based marketing manager.
"The wings (700m² each) are formed with a 1.3 times inventory and double reshoring; the centre (450m²) is formed with a double inventory and double reshoring.
"Only 3,000m² of MevaDec slab formwork is required to supply the entire construction process," he adds.
Slab areas of different sizes are poured every day, which means that one complete level in the core is completed every third day.
According to Lutzow-Rodenwoldt, two factors help to keep up this fast pace: "Firstly, the MevaDec drop head with quick-lowering system, which allows for stripping the panels and beams while the props remain as reshoring. Also, the low weight allows the panels to be transferred to the next floor level by using lifting gear."
In addition, Lutzow-Rodenwoldt claims there is no need to replace the MevaDec forming face "despite hundreds of re-uses at great heights". For conventional plywood, facing as few as 30 re-uses would have been the end.
Delays in the construction process and an enormous logistic effort would have been the consequence.
"But with MevaDec's composite plastic forming face, the system guarantees facing will never have to be replaced, regardless of the number of re-uses during the building of the Burj Dubai."
The result is there is no downtime during the construction process: "The guarantee is being confirmed daily in practice and is proven further by adherence to the exceptionally tight scheduling," adds Lutzow-Rodenwoldt.
"Even asymmetric layouts are formed with MevaDec's, "especially the polygonally curved slab edges are formed with tailored-custom panels".
This saves time-consuming on-site preparation and assembly.
"Only five different types of custom panels are required, and these easily cope with every re-use without changing the facing.
"As the Burj Dubai nudges closer to the 80-storey mark, it is almost halfway to the final estimated 160 storeys that will make it the world's tallest tower when it tops out in late 2008."
In the three-day cycle, day one sees the pre-assembled cage installed inside the formwork, and inspected during day two. Concrete is cast on the third day and after ten hours the form is struck and jacked up to the next floor.
While the final height remains a secret the general consensus around town is that it will hit the 800m mark, thus potentially overtaking the world's current tallest building Taipei 101, by around 300m.
To make all this a reality requires a combination of rock-solid planning, innovative construction techniques and a massive labourforce, and not to mention plenty of nifty formwork.