Using a novel vertical production line, builders of a futuristic U.K. observation tower recently completed the 162-m-tall steel mast around which a sleek doughnut-shaped pod will rise and fall.

For five weeks ending late last month, workers on the beach at Brighton fed sections of the 3.9-m-dia tower, each weighing as much as 85 tonnes, into the base of a special frame and jacked them up into position.

Most of the mast’s assembly work took place near the ground level, reducing the hazards of assembling the heavy steel tubes from the bottom up, says John Roberts, engineering director for the tower’s developer, Brighton i360.

The installation system is “a world first,” believes Neal Mardon, project manager for the i360’s contractor, Krimpen, Netherlands-based Hollandia Infra B.V. “There’s no benchmark,” he adds.

Beginning next summer, the 90-tonne glass-enclosed pod will transport as many as 200 people at a time up and down the $70-million tower at the site of a defunct Victorian-era leisure pier.

Conceived by David Marks and Julia Barfield, managing directors of London-based Marks Barfield Architects, the tower will be a vertical replacement of the West Pier, says Roberts.

The architects, as investors in Brighton i360 along with Roberts and two others, developed the project after selling, a decade ago, their one-third interest in the commercially successful London Eye Ferris wheel. They had developed and designed the 135-m-dia wheel as the world’s biggest of its type when it started turning in 2000.

For its next venture, the team ruled out another wheel elsewhere on economic grounds. Large Ferris wheels are expensive and viable only “in very few locations because of the number of passengers [you need],” says Roberts.

Having worked on London Eye’s engineering with a design firm later acquired by Jacobs Engineering Group, Roberts retained his relationship with the architects. He now has a dual role that includes acting as executive director of operations at Jacobs U.K., which is designing the Brighton tower.

The mast is encased in perforated aluminum, increasing its diameter to 4.6 m. From a design standpoint, the main problem with the tower is vibration, caused by its height and small footprint, says Roberts.

The steel tube’s skin reduces the vibrations perpendicular to the wind direction caused by vortex shedding, he adds. Eighty tuned liquid mass dampers distributed around the mast’s inner circumference at various levels mitigate vibrations in the direction of the wind.

Keeping the London Eye team together, i360 negotiated a main contract for the whole tower project with the wheel’s builder, Hollandia. The tower itself accounts for about a third of the total cost. The contract also includes linked buildings and the pod, says Roberts.

To finance the project, shareholders in i360 “have contributed [$1.5 million] in equity and over [$7.6 million] in loans,” explains Marks, who is i360’s chairman.

Loans from the local authority and a public agency completed the financing. The authority will share a small portion of ticket sales.
With financing and approvals secured, Hollandia broke ground in July 2014. Initial work focused on utility diversions and construction of the tower’s 3-m-deep foundation slab.

The mast was assembled in 17 sections, called cans, which are bolted together vertically through flanges. Made with 8-centimeter- to 2-cm-thick steel, the cans are generally 12 m tall, but shorter at the lower levels, where they are heaviest, and 14 m at the top, says Roberts. A 4.25-m-tall can, bolted to the slab, was the starting point for the tube’s vertical launch.

Rather than stack the cans from the bottom up, Hollandia developed a vertical assembly line within a jacking frame that stood more than 50 m above the base.

The contractor fabricated all the cans and the jacking frame at its yard next to the River Ijsel, east of Rotterdam. In June, the Dutch firm then barged all the components and assembly equipment on two trips to the beach site, some 80 kilometer south of London. The components never touched a public highway.

Hollandia first set up a launch platform some 10 m above ground atop the bottom two cans. Later, crews craned in the tube’s top four cans onto the platform, while completing the jacking frame.

After bolting together the four cans , the team jacked them high enough to allow crews to slide another onto the platform. With that can bolted to the tube above, Hollandia repeated the jacking cycle.

It took 10 cycles to complete the tower with jacks lifting nearly 1,000 tonnes for the last operation.

The installation took a little longer than planned. “There were times when it was too windy” to jack, says Mardon. Otherwise, he adds, the work went off without hitch.