John Roberts has been a Chartered Member of the Institution for forty years. Here he discusses his work on the British Airways i360, a remarkable new attraction on the Brighton seafront which was presented with the Supreme Award for Structural Engineering Excellence at The Structural Awards 2017. 

I have been very fortunate to have been involved in numerous interesting and exciting feats of engineering, particularly innovative leisure structures like the British Airways i360 -  having also worked on ‘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 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. David sadly passed away this month - a terrible loss to architecture and engineering. Without David’s vision and passion neither the Eye nor the i360 would have been realised.

David produced the initial design 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 was swift - for example the key activity of erecting the tower was completed in a period of just 10 weeks.

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 remaining 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 (162m 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 20m per second (at a 10m reference height) when the pod is fully elevated. The tower is fitted with 76 ‘sloshing liquid dampers’, which help to prevent lateral movements.

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 stands alongside Brighton’s Victorian era piers, which were major engineering feats of the time. 

The tower opened for business with paying passengers on August 4 2016 (having been handed over by the contractor at 12.00 noon that morning!). Notwithstanding the 10 years or more of effort that had led up to that day we were understandably anxious that it would operate without any issues and that the public would turn up to enjoy it. In the event we have carried more than 500,000 passengers in the first 12 months of operations, and are really pleased with the feedback and reviews from visitors and residents alike. We had monitored the tower during storm “Barney” in November 2015 (shortly after the tower had been completed) with measured wind gusts exceeding 75mph, and this demonstrated the excellent performance of the tower and the sloshing liquid dampers. 

I am immensely proud that the British Airways i360 has been shortlisted for an award at my own professional institution, but I recognise the fantastic quality of the other shortlisted projects and regard it as a great honour to have even reached this stage in the competition.
Explore The Structural Awards shortlist.

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