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Arcelormittal Orbit: Mittal's twisted tale

A twisted muddle of steel or an elegant industrial urban sculpture − whatever the judgement on the aesthetic appeal of the new ArcelorMittal Orbit, it is a feat of precision structural engineering.

A work of public art

The Orbit is the latest addition to the London 2012 Olympic Park, but is not part of the original park plan. it is the product of a competition spawned by London mayor Boris Johnson to find a work of public art and a visitor attraction at the 2012 Games main venue.

Just one year ago, Johnson announced that sculptor Anish Kapoor had created the winning design. But this has been a celebration of engineering as much as it is a work of art. Renowned Arup structural engineer Cecil Balmond worked with Kapoor from the beginning bringing practicality and an ambition to ensure the complex design could be built.

The result is what can most easily be described as a 114.5m tall observation tower composed of a continuous looping lattice of tubular steel, painted vibrant red. More artistically it is a sculpture with a continuous journey from the start to the finish − or an orbit, hence the name.

London’s answer to the Eiffel?

As it is a tall metal structure, comparisons with the Eiffel Tower are almost inevitable. The team at steel giant ArcelorMittal − sponsors of the project − have ambitions that it will rival the Paris icon in years to come, even if it is not as tall.

The 324m tall Eiffel Tower dwarfs the Orbit. But ArcelorMittal head of global research and development Greg Ludkovsky says it is not about the height but the shape.

“It is a challenging structure. It’s not boring […] And whether you like it or hate it, it certainly will not leave you unemotional.”

“It is a challenging structure. It’s not boring. And whether you like it or hate it, it certainly will not leave you unemotional.”

Greg Ludkovsky

The firm believes the Orbit has other advantages, pointing out that the cast iron Eiffel Tower could now be built in steel at a third of its weight. In addition, the Eiffel Tower with its four legs has a predominantly regular shape. The Orbit has three “legs” and is not a uniform shape in any way.

“It’s a sculpture, it’s a structure, but it’s also a building,” says ArcelorMittal chief project engineer Pierre Engel. Not only is the firm funding most of the £22.7M total cost − it is paying £19.6M with the London Development Agency paying the remaining £3.1M − it is also providing all the normal grade, mild steel for the structure. The firm is also a tier-two sponsor for the Games.

Steel solution

The structure’s material is not incidental. While it was not stipulated in the early design, it is the only solution, says Engel. While he may be biased towards its benefits, he gives a clear reasoning for the declaration. The tubes that form the structure lend themselves to steel. It is ductile yet very strong; it makes for speedy erection; it has deformation capacity that allows it to flex − an important factor for such a tall structure. Steel is also adaptable to the complex shapes in the strucure.

And the Orbit is an extremely complicated shape. Around 9km of steel tubes − not one identical to another − connect via 900 connection plates to form trusses which create the bulk of the structure.

There are also a number of separate elements. The steel tubes − all straight − will connect to form an intricate geometric shape via connecting “star nodes”.

View from the top

The structure will also incorporate a two level, 20m diameter observation building with two platforms − one at 80m to include exhibitions, the other at 76m a flexible space for functions and special events.

The observation decks will afford dizzying views of the 100ha Olympic Park and across London.

They will be accessed via two lifts and an irregular spiral staircase. Visitors will ride the lift to the viewing platforms and will have the option of walking down the spiral staircase.

“The thing the team homed in on was the importance of the journey through the tower”

Francis Archer

Its towering height puts the Orbit 22m taller than the Statue of Liberty.

The engineering design unsurprisingly relied on computer programming to dictate the size and shape of the tubes and connections. While the appearance of the structure is one of continuous sinewy tubes, it is of course far from continuous.

“The thing the team homed in on was the importance of the journey through the tower,” says Arup structural engineer Francis Archer. “With a digital design tool we could investigate hundreds and hundreds of possibilities.”

Kiss and tell

“The tube has to kiss at various points to give stability. The real structural solution meant the tube turned into trusses.” The tubes are welded onto connecting plates that allow each point to be bolted to the corresponding adjoining piece. But the engineers on the job made sure the design could be realised. Despite each section being absolutely straight, the effect is one of fluidity.

One of the key practical considerations was the effect of wind loading on the structure. While the Olymic Stadium next door does give some shelter, the structure will be exposed to high winds and at 97km/h visitor lifts will be closed.

Maximum anticipated wind induced movement will be somewhere in the region of 20mm to 30mm. But sway is not so much a concern; more problematic are the vibrations caused by the wind, and subsequent discomfort suffered by visitors.

To counter this, a 40t pendulum-like mass damper will be suspended from the structure to counterbalance these movements and make it a more pleasant experience.

Under construction

Work to construct the sculpture is gathering pace. Enabling works began last year to create the structure’s piled raft foundation − comprising 49, continuous flight auger piles, 900mm in diameter, then steel reinforced concrete.

At the time of NCE’s visit, and in less than two months of working on the superstructure, the tower was already at a third of its final height − threatening to overtop the main stadium any day. It stands in the southern part of the Olympic Park in a prime location between the Stadium and Aquatics Centre.

It is an impressive achievement from what is essentially a team of three from Steelcraft Erection Services which is building the tower on site.But the simplicity on site belies a much greater effort going at the other end of the country to enable the build. The fabricator on the job is Bolton-based Watson Steel Structures which, like Steelcraft, is part of Severfield-Rowen.

ArcelorMittal produces the Orbit’s steel, of which around 65% of the primary steel is recycled, in Luxembourg via other parts of continental Europe where it is formed into tubes.

When it reaches Watson, the steel is subjected to high-tech scrutiny in the process of connection design and
fabrication.

A natural choice

The firm seems a natural choice, having already worked across the Olympic site on − among other structures − the main stadium, the Aquatics Centre and the Velodrome.

“We are very familiar with taking a drawing board concept and turning it into a reality,” says Watson managing director and Severfield-Rowen chief operating officer Peter Emerson. “It’s what we do […] however, in the case of the ArcelorMittal Orbit project, the degree of precision required was higher than usual. Its unique design meant that it would not be possible to make adjustments to the structure once construction commenced.”

“Its unique design meant that it would not be possible to make adjustments to the structure once construction commenced.”

Peter Emmerson, Severfield-Rowen

The result is that while creating the connections in Bolton, over 100 Watson staff are virtually building the structure there too.

The firm recently invested over £500,000 in British-made equipment for a revamped machinery centre.

The result is a place where computers and laser technology sit side by side in the plant to aid fabrication − something that is proving vital in obtaining the very tight 1mm to 2mm tolerances for the Orbit connections.

The accuracy is critical to ensuring the complex structure will work and Watson’s job is so intricate, the process involves virtually building the sculpture in Bolton before it is taken to site.

Connection speed

Watson received specifications and 3D computer models of the structure from Arup, and set to work. Some 900 connections, 1,800 steel connection plates and 600 star nodes − each requiring around 50 bolts − are required.

An oxy-acetylene cutting tool shapes the ends of each of the between 400mm and 500mm diameter tubes at the appropriate angle required for that part − “Not one pipe has the same profile as another”, says Watson production engineering manager Jed Hulme.

The 4m tall star nodes are particularly intricate − being the meeting point for a number of other connecting tubes.
To fabricate these, Hulme devised a series of jigs to hold each element.

This is where the computers come back in. A laser is used to spot reference points onto the steel held by the jigs.The laser points are plotted on the computer against the 3D model to ensure the steel is precisely where it should be in relation to the next connection. Adjustments can then be made before welding takes place.

Long descent

Watson is also fabricating the 38 stair modules and the 15 ramp modules for the lowest section to create the 480m long spiral descent from the observation deck. These have a solid base with a mesh wall and ceiling designed to allow a continued enjoyment of the views.

The stairwell, along with the design of an entrance pavilion and observation deck details including partial external walkways and concave and convex mirrors, are fine examples of Kapoor’s trademark interest in voids and space.

The pavilion entrance is designed to enhance this. It is a more solid tapered funnel-like canopy that begins 3m above ground level rising to 25m. There will be a 400mm deep shallow recess in the ground beneath the canopy, from which visitors can look up into the shaded red space above.

Watson is also responsible for the primary steelwork for the observation deck. This will be built at floor level before being craned into place. The fabricator began its work last autumn and expects to finish by the end of summer.

Legacy focus

The Orbit will is due for handover by 1 May next year, in time for the Games, but its legacy use is the focus now.

The Olympic Park Legacy Company launched procurement for an operator for the attraction on 7 January and expects to award a 10-year contract in June.

It is estimated that around 1M visitors will head to the Orbit every year, generating up to £10M per year in revenue, including from catering, private functions, retail and merchandise.

What they said

At 114.5m tall and a striking red the structure will be hard to miss.

It is said to be designed to emulate the impression of the Forbidden City’s bold colour standing out from a blue sky background in Beijing. Here’s what the promoters say.

“We set out to create a transformational piece of art that will be an iconic symbol for the Olympics and also a new landmark that will endure long after the Games themselves.”
ArcelorMittal chief executive and chairman Lakshmi Mittal

“It is the commission of a lifetime.”
Sculptor Anish Kapoor

“He [Anish Kapoor] has taken the idea of a tower, and transformed it into a piece of modern British art.”
London mayor Boris Johnson

“The collaboration between Anish Kapoor, Cecil Balmond and Lakshmi Mittal bridges art, architecture, engineering and business to produce a new landmark for London.”
Tate director Sir Nicholas Serota, competition adviser

Project timeline

  • February 2009

ArcelorMittal chairman and chief executive Lakshmi Mittal has a chance meeting with London mayor Boris Johnson at the World Economic Forum in Davos and agrees to support the scheme and provide steelwork.

  • September 2010-October 2010

Enabling Works on site

  • October 2010

Piling completed

  • November 2010-January 2011

Substructure

  • January 2011-September 2011

Superstructure

  • October 2011-December 2011

Lift installation

  • October 2011-February 2012

External envelope

  • October 2011-February 2012

Mechanical and electrical
Target date of March 2012
Handover to the Olympic Park Legacy Company (OPLC)

  • 01 May 2012

Handover by OPLC to the London Organising Committee of the Olympic Games

  • 27 July 2012 to 12 August 2012

London 2012 Olympic Games

  • 29 August 2012 to 9 September 2012

London 2012 Paralympic Games

  • 31 October 2012

Handback to the OPLC

  • 2013

Queen Elizabeth Olympic Park opens

Readers' comments (2)

  • All that talk about how wasteful the bird's nest steelwork was and how different the London designs would be...

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  • I can't help but agree with the previous comments. This should have been a wind turbine or alike to ensure we meet and possibly exceed the obligation we made to ensure the London 2012 games would be sustainable. More over this seems like nothing more than vanity.

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