How the Damac Towers project defies gravity

Paramount proudly presents Damac Towers — from the pumps that brought you the Burj Khalifa

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A project as daring as the Damac Towers by Paramount demands a star cast, and Damac Properties has found that team in none other than Turkish contractor TAV Construction, a duo of crane rental firms and the supporting roles of veteran concrete suppliers, Unibeton and Unimix.

The project’s final height of 250m at first glance appears modest in comparison to the various record-breaking projects being spun out across the emirate — including the slew of residential giants in the marina — but with four towers, the project’s combined structural height equates to 1km.

From contractor to concrete suppliers, many elements of the team constructing this megastructure were also deployed on the site of the Burj Khalifa, and even down to the nuts and bolts of the project — the cranes and concrete pumps that make it tick — several of the unit models are identical on both projects.

The project employs eight tower cranes in total, four climbing internally, four externally — two of them offset from the building by 3m; the other two offset by over 15m.

“It’s quite unique to connect a tower crane at a distance of 15m — it can be longer, but it is rare and not preferable,” notes Levent Iren, deputy project manager, TAV Construction. “However, due to the building design and the structural requirements, we went for it.”

The cranes are carefully connected to the core walls of the building “in a way that has minimal effects on the finishing works”.

Four of the cranes are of the US brand Terex Comedil (2x 14t lift capacity; 2x 10t capacity), while two are from France’s Manitowoc Potain and one is a Spanish Linden Comansa model.

Nouman Fouad Trading, of the NFT Group, distributes Potain in the region; Al Rana Equipment & Machines Trading Est. (AREMATES) distributes Comedil and Comansa.

Confined within a tight project footprint of just 10,000m2, the eight cranes are all luffing jib models, both to prevent the cranes from mutual obstruction to keep the risk of collision to an absolute minimum — an endeavour assisted by the use of anti-collision software.

Iren highlights that anti-collision software is “not mandatory according to the safety regulations in the UAE, but we believe it is helping us to avoid any accidents”.

He adds: “You don’t see the benefit if you have no problems, but we believe it helped a lot — we have had zero accidents.”

The external cranes are the highest on the project, standing several dozen metres above the top of the structure; they will also be used to disassemble the internal cranes once the project reaches the roof and nears completion.

“The initial intention was to remove two of the external cranes at a later stage — but we decided that we could just extend them and continue to use them to serve both the podium and the towers,” explains Iren.

It has since transpired that the additional support is extremely beneficial, because each tower now has two dedicated cranes, with the two heavily offset cranes serving as backup in case of a breakdown on either tower.

CRANKING IT UP

The contractor is ‘climbing’ each of the eight cranes of the project every three floors, using hydraulic jacks — with the internal cranes fastened eight floors or 35m down into the towers to the structural cores and resting on reinforced post-tensioned slab sections.

“They have three collars anchoring the cranes to the core wall on alternate floors — so every three floors we remove one collar, shift it to the new floor, press a button and the cranes climb,” explains Iren.

“We have a specialist third-party team to jump the cranes, and it takes about one-and-a-half days to complete the process, and we don’t stop the crane totally while the operation is going on, because we first need to prepare the ties to connect it to the building.

“During this time the crane can still operate, but once you turn on the hydraulic systems to climb it, then you need to stop and vacate the area — and we only jump during in the daytime due to safety concerns. The cranes then take 3-4 hours (roughly the same for both internal and external) to climb up before we can lock them, complete a 12-part check and continue with operations.

The positioning of the external cranes also had to be determined at the very outset of the project, to allow reinforced foundations to be cast at the water-proofing level.

“The foundations for the free-standing cranes are four masses of concrete measuring 6m by 6m across and one metre high, with the crane moorings embedded before casting,” explains Levent. “Two are embedded in the soil below the raft foundation — the other two are temporarily situated on the slab of the podium’s parking levels and will be demolished once we dismantle the cranes.”

Once the internal cranes are jacked up, the holes left behind are immediately closed — laid with rebar and formwork and filled in manually with concrete delivered by the tower cranes to the cantilevered loading platforms.

There are nine loading platforms on each tower supporting the lifting activities of the cranes (36 in all), as well as four construction hoists on each tower: two for materials and two for people (16 in all). For these details, the concrete is transferred to the desired location using concrete buckets and trolleys. This process is limited to lower volumes — typically only 3m3 or 4m3 of concrete.

FEELING PUMPED

The second challenge of the project is the delivery of supplied concrete to the top of the four 200m-high structures in a single motion. To achieve this there are four stationary pumps at grade and pipelines up each tower.

Iren explains: “At the top of each structure there is a placing boom to lay the concrete into the slab formwork. The operator on top has a remote control, and when the concrete arrives on site in the mixer, it is poured into an intake bucket for the stationary pump and delivered to the top of the tower. Each placing boom has a 28m radius, covering its entire slab, including the vertical components.”

When it received the concrete supply quotes from Unibeton and Unimix, TAV specifically requested the use of Putzmeister or Schwing machines to ensure their durability and operational efficiency — though the latter were unavailable. Four powerful Putzmeister BSA 1400 D units were finally selected for the project.

Iren notes: “These are the same pumps as used in the Burj Khalifa — two of them from Unibeton and two from Unimix.

“Our concrete suppliers also worked on the Burj Khalifa, so it’s not only the equipment, but also that expertise with the mix design and everything else involved.”

PRESSURE RISING

In the end, it is the pipeline conveying the concrete rather than the equipment that face the more significant problems.

“As you go higher, pressure is a problem, and you face blocking of the pumps or bursting of the pipeline during casting — so at certain stages we have to change the mix to reduce the pressure or to increase the workability,” says Iren.

“The are many parameters with the concreting. The concrete must be pumpable but also workable — viscous like honey to ensure there is good bonding, but not thin like water, or it will segregate.”

Segregation is a risk at height, because without sufficient cohesion between the ingredients, the aggregates will begin to settle in the pipe on the way up — delivering a non-homogenous mixture to the placing boom and potentially blocking the pipeline and causing it to burst.

Iren notes: “This is with the supplier: they have their own quality control checks, laboratories and quality checks. We also do our own slump and flow tests before each truckload is pumped up.

“Even so, we have still experienced some bursting. The pumps deliver 246hp and are more capable at the pressure, but the pipeline needs constant maintenance.

“At the outset, it is important to select a pipeline for your maximum height. For this project, we are using a special pipeline composed of 6mm-thick material.”

STILL RISING

Each Putzmeister can pump 30m3 to 40m3 an hour at the 80% complete project height of 200m, with 48 out of the 56 floors complete.

“The higher the placing boom the longer the duration of the pumping operation,” notes Iren. “To pump the 200m3 required for each slab (the vertical components required 300m3) it takes between five and six hours, and with the quality checks at the bottom and then the top, it takes six, or even seven, hours.”

However, Unibeton and Unimix have provided the necessary logistical support and supply resources to ensure that TAV can continuously pour on the four towers at the same time.

“We have our own resource as well. We can divide our pouring team into four or even five, because the schedule of the project will not allow us to stop in one location and continue in another location — we must go ahead with all four towers at the same time,” notes Iren.

As the towers rise, the aggregates also get smaller and the admixtures more expensive.

“We then have to tamp the concrete by vibrating it very gently. Because it is a thin slab, we have to vibrate it hard enough to take the air bubbles out, but not so much as to again risk causing segregation,” Iren adds.

The project does not test the limits of today’s leading concrete pump technology. The most advanced units can now pump concrete to heights of 750m in one go — a capacity that was ironically not available during the construction of the Burj Khalifa, where the concrete had to pump the concrete in stages.

However, it is testament to the versatility of the equipment systems employed that so much could be achieved: from the operation of eight luffing jibs in a comparatively confined space to the simultaneous pouring of 800m3 across four slabs at a height of 200m — all the while maintaining the homogenous mix necessary to ensure the structural strength.

FINAL RESULT

Glimpsing the future, one of the four towers will host the Paramount Hotel Dubai, while three will be serviced apartments managed by Damac — all scheduled to open in Q4 2016.

Niall McLoughlin, senior VP for Damac Properties, notes: “It’s not one project; it’s four projects with a shared podium. We have four towers going up, each 250m-high.”

Paramount Hotels & Resorts is meanwhile developing the design of the towers to reflect the creative history of Paramount Pictures.

McLoughlin explains: “It’s not in your face. The idea isn’t that you walk in and see Marlon Brando staring back at you off the wall. It’s more about the feel and the atmosphere from all those movies from across the years.”

And while guests will be able to watch any of the 3,500 movies that Paramount Pictures has produced in over the last 100 years, Damac is keen to avoid fixating on these elements.

McLoughlin concludes: “People are going to be living in this project, so if it was movie-esque everywhere you went, it would be a too bit intense to live there for five or 10 years.

“It’s a bit more classic: it’s going to be a classy five-star experience — so that’s why it’s much more about the feelings and ambience.”

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