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Site visit: Dubai Frame, UAE

ARP delves into the technical nitty-gritty of building Dubai Frame, the 150m-tall landmark currently under construction in the Emirate’s Za’abeel locality

Dubai Municipality’s Dubai Frame consists of a pair of 150m-tall concrete legs and a 93m-long steel bridge.
Dubai Municipality’s Dubai Frame consists of a pair of 150m-tall concrete legs and a 93m-long steel bridge.

That Dubai is proud of its architecture is no secret. And rightly so. Home to Dubai Creek, Burj Khalifa, and Dubai Mall, the Emirate has amassed a formidable reputation over the years for combining traditional design philosophies with modern engineering techniques.

Within this context, it isn’t altogether surprising that decision makers are now working on a project that will both encapsulate and enhance Dubai’s greatest architectural achievements: Dubai Frame.

Al Rostamani Pegel (ARP) is acting as the main contractor for this ambitious development. The 150m-high, 93m-wide structure has been designed to resemble a giant picture frame.

Once completed, the Frame will offer panoramic views of the city’s best-known architectural landmarks, both old and new. On one side stand historic locales such as Bastakiya, Bur Dubai, Karama, and Deira. Turn around and you’ll see ‘New Dubai’, with modern masterpieces such as Burj Al Arab, Emirates Towers, and Burj Khalifa.

The project’s developer, Dubai Municipality expects the Frame to attract more than two-million visitors per year following completion. Encouragingly, its striking aesthetics have already garnered significant attention from across the UAE, according to Richard Browne, operations manager at ARP.

“It is quite an unusual structure, and in many ways, it’s more like building a bridge,” he tells Construction Week. “We’ve been asked on numerous occasions by people if they can buy an apartment [at the project], because they saw these two cores going up and didn’t understand what it was about.”

The Frame consists of two 150m-tall cores, known as ‘legs’, which are linked by a bridge that will allow visitors to walk across the structure. Each leg features fire stairwells and panoramic lifts, which have been supplied by Thyssenkrupp.

The first two floors of the columns were constructed using conventional shutters; the remainder were built with a self-climbing formwork system, which covers three levels at a time. The formwork’s floor-to-floor height is 3.1m.

The Frame boasts 46 floors in total, as well as a roof level. Tobias Florian Heilig, senior construction project manager at ARP, says his team devised this automated, self-climbing system in conjunction with formwork and scaffolding specialist, Peri.

“After the first eight or nine climbing steps, we reached a cycle time of four days, and sometimes even three-and-a-half – so that was very good for us,” he recounts.

A key factor for the construction team was to ensure the towers were precisely measured, continues Browne.

“When we got to the top of the tower, we had a tolerance of about 15mm,” he recalls. “So we have a 150m-high tower that’s built within a 15mm tolerance – that’s quite unusual.

“We employed a specialist designer to monitor and simulate the towers [in order to gauge] the effect of having the crane anchored to them, the wind, and the hoist. So at every floor, before we poured [concrete], we would carry out a level check, an alignment check, and so on. That was done rigorously at all times of the day,” he emphasises, adding that this process helped to ensure vertical and horizontal alignment throughout the construction process.

Indeed, the towers’ vertical alignment has been a vital part of the construction process. The team had to consider how the concrete structures would come together once the bridge section had been lifted.

“You might find some towers tend to twist or turn as they go up, but [the Frame’s] are remarkably straight,” Browne notes. “We had to be very precise about that because when we come to steel erection, we’re [dealing with] very tight tolerances. There were also predictions from a computer model [designed to test whether] as the bridge was lifted up, the two towers would actually move in together,” details Browne.

The Frame’s structural integrity and design would likely have been affected had the bridge been lifted in such a manner. Weather conditions at 150m made it all the more important for the construction team to gain a clear understanding of how the legs would behave once the bridge was raised. These factors were accounted for by a number of analyses conducted by ARP. The contractor’s full report was also shared with the project’s client and consultant.

Eventually, the towers were pre-cambered from their 80m-high 24th levels by up to 45mm to compensate for the lifting process. ARP and its peers achieved tolerances at the top within 8mm from the theoretical location. This process was conducted in conjunction with Arcadis legacy outfit, Hyder, which was appointed as the project’s structural designer.

“People will tell you a lot of things about concrete,” Browne says. “But if you can get a concrete tower up at 150m with an 8mm difference, then I think it’s fair to say [you’ve done] pretty well.”

The Frame’s steel bridge was constructed atop a podium, which featured concrete-reinforced beams to take the load off the component. Browne contends that ARP’s bridge-engineering skills contributed significantly to his team’s victorious project bid.

“One of our [advantages] was that we proposed to build the podium, and then use that podium as a temporary structure to erect the steel on top,” he explains. “This involved some temporary works, analyses of the permanent podium roof, and additional reinforcements to make sure the columns could take the weight – because the bridge itself was 800 tonnes of steel.”

The Frame’s bridge consists of steel tubes, which are connected with plates as thick as 75mm. ARP claims that there are only three rolling mills on the planet capable of producing these components.

The tubes were manufactured in China and shipped to the Emirates. Singaporean engineering firm Eversendai was appointed as the specialist sub-contractor with responsibility for their installation.

The project’s 7.6m truss, meanwhile, posed a logistical challenge for the Frame’s construction team, whose chief concern was its safe transportation from a Sharjah fabrication yard. Due to its size, the truss had to be temporarily fixed together and transported overnight before permanent welding could commence.

The first welds took around 48 hours, Browne estimates, adding the volume of welding operations alone justified the Frame’s high quality-control standards.

“The bridge is 150m in the air; we had to be certain whatever welding was done was tested,” he remarks.

“Eversendai, ARP, and Arcadis engineers were on site while every weld was tested. [These tests were conducted] before [the truss was] taken off the ground. The whole structure was then coated with intumescent paint,” Browne recounts.

However, the construction team’s most pivotal moment came in October 2015 when the bridge was lifted onto the twin legs. This lift operation was meticulously planned over a period of four months.

A temporary jack-support steelwork system was anchored to the superstructure; the bridge had four anchor points at each end. The pre-lift operation involved “hanging” the bridge to ensure that the jacks and strands were operating safely.

The bridge lift took 48 hours in total, and was supplemented by a continuous monitoring survey. ARP and Eversendai worked with VSL to conduct the installation. The nail-biting job completed without incident; something that Browne attributes to effective communication between the three contractors.

For a lift of this magnitude, safety had to be the primary concern, he continues. “Because at the end of the day, we were lifting something that weighed 800 tonnes 150m into the air.”

The fact that the bridge’s jacks “are not available off the shelf” also represented a challenge for Browne and his colleagues.

“You have to plan your lifting operation well in advance to ensure that when you want to lift the bridge, the [right tools and materials are] available,” he explains.

“The other thing is that as the bridge went up, the structure actually moved. We [had allowed for] it to move by 45mm,” he adds with a smile – in reality, the structure only moved within a range of 22mm and 33mm.

Once the main lift had been completed, the team spent four days aligning the truss. Following the completion of final alignment works, it was locked into place with temporary steel braces whilst permanent welded connections were completed.

Heilig admits the lifting process required “intensive calculations”.

“Monitoring [was necessary] to make sure we’d picked the right time to lock in and start welding,” he continues, adding that handrails and other safety measures were installed prior to the lift.

Of course, the bridge will ultimately form the Frame’s viewing platform – a crucial operational component of the structure. To aid facilities management (FM) activities, ARP integrated a window-cleaning gantry. This building-management component features an extendable arm that will stretch up, over, and under the soffit of the bridge.

Heilig comments that the Frame looks “very simple when you see it now”; an effect that belies the project’s structural complexity. “However,” he continues, “it’s a team effort and we have a lot of fun here. [ARP] has a very open relationship with its clients.”

Browne concludes: “We’ve been diligent with regards the alignment of the tower, sorting out every little detail. Because after all, we’re building an iconic structure for Dubai. 20 years [from now], when driving down Sheikh Zayed Road, we’ll be able to say: ‘We built that’.”

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Construction Week - Issue 754
Nov 23, 2019