Published: 15 December 2015

A tower like no other

Leisure Structures

The completed i360 pod

John Roberts has been a Chartered Member of the Institution for forty years. Here he discusses his career and work on the British Airways i360, a remarkable new attraction planned for the seafront in Brighton, England.

I decided to study civil and structural engineering at university after work experience on a Bristol building site, which I did during the school summer holidays. It was hard work but relatively well paid, and I imagined that it would be better still if I was a qualified engineer. It really has been a remarkably rewarding career choice.

I have been very fortunate to have been involved in numerous interesting and exciting feats of engineering. If I had to list stand out projects, I think I’d pick the ‘Pepsi Max Big One’ rollercoaster at Blackpool Pleasure Beach, and the London Eye observation wheel. Almost everyone in the UK will know at least one of these two attractions: between them they have so far carried over 100 million passengers – a fact that never ceases to amaze me!

The i360 is the latest leisure structure on which I’ve had the privilege to work. It’s a kind of vertical cable car, where a glass, doughnut-shaped viewing pod lifts 200 passengers to a height of 450 feet, offering 360 degree, 26 mile views of England’s south coast. It was conceived by David Marks of Marks Barfield Architects, who also was the originator of the London Eye, and I have been involved as the project engineer from literally the first day.

The initial design was drawn up in about 2003, with most design work being completed by 2006/2007. The project was delayed by the financial crash of 2008, so work on site didn’t begin until 2014. Once we started, progress has been swift - for example the key activity of erecting the tower was completed in a period of just 10 weeks, and the i360 project will open to the public during the summer of 2016.

There are many other viewing towers around the world, but the i360 is radically different to them all in terms of both design and engineering, and also in terms of the viewing experience. One unique feature is the fact that passengers can walk around inside the pod as it slowly ascends the tower – where other viewing towers have the passengers remain seated throughout.

As the world’s tallest moving observation tower, we faced a number of challenges around its design and erection. The i360 tower is exceptionally slender (162 m tall with only a 3.90m diameter), so its dynamic behaviour in wind was the key design parameter. As well as the usual “50 year” storm conditions, it has to perform satisfactorily (in terms of acceleration limits) during wind speeds of up 20 meters per second (at a 10 metre reference height) when the pod is fully elevated. The tower is fitted with 76 ‘sloshing liquid dampers’, which help to prevent lateral movements.


Barge unloads elements of the i360 onto the beach site

We also had to think carefully about how we erected the tower, which was carried out using a “top-down” jacking system, without a crane. All 17 pieces of the tower were delivered by barge onto the beach at Brighton, directly adjacent to the site. Further, each part arrived fabricated with all components fitted - such as ladders, platforms and guide rails - so that nothing had to be added on site.

The i360 is comparable to the London Eye, at least in terms of technical innovation. In both cases there were other existing designs (for moving towers and Ferris Wheels), but both the i360 and Eye are massive step changes, featuring significant improvements. In that respect it’s appropriate that the British Airways i360 will stand alongside Brighton’s Victorian era piers, which were major engineering feats of the time. 


Drone view of the completed tower, with pier in foreground
 
I have been pleased to give a number of talks to local residents in Brighton, with interest obviously peaking as we head towards opening. I particularly enjoy talking to passers-by, who stop to look up at the completed tower. That’s one of the great things about the i360 – it’s just the kind of exciting, unique structure that get members of the public excited about structural engineering, and hopefully help to introduce more young people to engineering careers.


A Cg image of the finished tower

 

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