British Airways i360 (The London Eye’s Little Sister)

I went down to Brighton for the day to hang out with one of my friends from there. She toured me around and, of course, we ended up on the beach. She pointed out to me, in the distance, a huge column and told me it was their brand new observation tower. She also said it was pretty controversial because it was built with taxpayers dollars, so I thought it would be interesting to do more research into.


Structure Information

Figure 1: My View of the i360 on Brighton Beach

This observation deck on Brighton Beach is called the British Airways i360. The BAi360, as British Airways calls it, cost £46 million to design and build. It was funded by Brighton and Hove City Council, Coast to Capital Local Enterprise Partnership, and Brighton i360 Ltd. Brighton and Hove City Council was loaned the money from the Public Works Loan Board and Bright and Hove City Council receives a potion of the profits. The observation deck opened in the summer of 2016 and has already begun to promote other development along the shoreline in Brighton. [1]

The BAi360 can be used as an event space as well as for the typical 25 minute “flights” to the top. 175 people can ride in the pod at the same time! The BAi360 website boasts that the structure itself is 20 feet taller than the London Eye, which is considered the BAi360’s “sibling.” [1]

Speaking of the London Eye, the architect for the London Eye, Marks Barfield Architects, was also the architect for the British Airways i360. The structural engineer on the project was Jacobs. [2]


Historical Significance

Figure 2: i360 Construction [2]

The British Airways i360 has won many awards, but the most notable awards are being the world’s tallest moving observation tower in 2017 and holding the Guinness Record for the world’s most slender tower. The construction process was the first of its kind, without cranes for the height addition and from the top to the bottom, which I’ll discuss further in the structural analysis. This construction method meant that construction workers were only needed on the ground, which is must safer than being 162 meters in the air. Figure 2 shows how much shorter the crane used in construction was compared to the completed tower. The liquid dampers used were also revolutionary in the UK. [3]

 


Cultural Significance

Figure 3: The i360 at Night [2]

The i360 seems pretty out of place in Brighton next to the Brighton Pier with arcade games and festival food, and it seems some locals agree. The i360 gained many nicknames, typical of the British, one being the iSore, another the Brighton Pole, and many others which are very inappropriate [4]. Figure 3 shows how tall the i360 is compared to the rest of the shoreline.

The investment process was also extremely controversial because the construction was just getting started as the recession hit and suddenly there wasn’t money for the structure. Up until then, it was to be only privately funded. In 2012, Brighton and Hove Council pledged enough money to get the project restarted, and in 2014, it pledged even more money when more funding walked out the door and the architects could only put up so much to keep it going. [5] In an effort to subdue these criticisms, local residents receive half-price tickets and each public school students in Brighton and Hove got a free tickets the summer the i360 opened [1].

With revenue being what was expected and the new development starting in the area, it seems that the i360 is helping the economy in Brighton and promoting even more tourism. It also seems to commemorate the old West Pier that was falling apart and eventually burned down (the arsonists were never caught), which metal skeleton just sits in the sea now in front of the i360.


Structural Art

Despite the public backlash and perhaps its out-of-placeness, I do think that the BAi360 is structural art.

The efficiency is obvious – with the recession, the architects and engineers were under huge economic constraints. On top of that, being the most slender tower in the world means the i360 really doesn’t use much material. My friend from Brighton told me that most of the area is in the Green Party, Brighton runs some buses off of recycled oil from making fish and chips, and there is a wind farm in the sea for energy, the i360 even reuses its energy from descending to go up the next time; all of which indicates that being efficient is extremely important to the area.

As far as economy, the construction method was absolutely considered in the design. From the architects that came up with lifting the London Eye from the River Themes in under a week, the i360 was built using jacks and keeping construction workers on the ground because of the huge wind loads at the top of the i360.

Elegance may be harder to see because of the location of the i360, but it is clear that this structure’s load goes straight into the ground, since it is just a column. There is nothing extra to hold up the column and the simplicity truly makes the i360 structural art.


Structural Analysis

As mentioned earlier, the i360 was thought up by the designers of the London Eye and had a novel construction method. The tower itself is made of steel, covered with perforated aluminum to prevent wind vortices. Inside the tower are 78 jugs of Australian water to further resist wind loads. The construction was done by transporting pre-made materials on a barge to the beach. A jacking frame was put up and 17 50-100 ton “cans” were jacked up, like you’d jack up your car to change a tire, but much larger. [3]

Due to the wind, there is a little more complexity to the i360 tower than once first thinks. The columns is the first structural component I first thought of, the second being the observation pod. After doing research, the liquid damping system is the final structural component to consider. The liquid dampers were “tuned” to the three most common natural frequencies of an undamped tower [7].

Figure 4: i360 Load Path

The tower is 162 meters high and 3.9 meters in diameter, 4.5 meters including the covering [3]. The viewing pod carries 200 passengers and goes up to 138 meters [3]. The pod is 18 meters in diameter and weighs 94 tons [8]. The tower only closes once wind gusts are up to 44 mph, which is 243 N/m2 for this structure according to a velocity-pressure chart [5]. The foundation is 6.5 meters deep to hit chalk rock, and because of tides, the base had to be able to sit in water. The foundation is 4,150 tons while the tower is 1,200 tons. 200 people can weigh about 18-20 tons, and they need to be able to stand all on one side of the pod in case something interesting is happening for them to all look at. The code in Britain for wind loading is to withstand “the worst three second gust in the middle of the worst storm which occurs on average every 50 years.” Apparently, this translates to the structure being able to deflect over a meter safely. There were redundant measures put in the tower for dynamic loading, such as random outstands to “confuse the wind,” as Dr. Stewart would say. [6]

The load path for the i360 is very simple: the mass from the pod goes to the tower and then from the tower the load goes to the foundation. The load path can be seen in Figure 4.

Since the pod will only operate at conditions under 44 mph gusts, I chose to analyze the worst-cast scenario with 44 mph winds. This includes all of the people being at one point on the edge of the pod and 44 mph winds creating pressure along the entire structure. With these assumptions, I calculated maximum moment and maximum shear, which are at the base of the tower since the tower can be treated as a cantilever, as well as the reaction forces of the foundation on the tower. The calculations and diagrams I used are shown below. 

The idea of the the i360 came from the architects, not the city, which is somewhat unusual. The i360 was modeled in a computer, and views of the structure with the town of Brighton behind it were presented, as well as views of what the inside of the pods would look like during flight. Figure 5 shows the i360 from a beach-view while Figure 6 shows the inside of the observation pod. These models were shown to Brighton and Hove Council and members of the community.

Figure 5: i360 Model [9]

Figure 6: Inside Observation Pod Model [10]


Personal Response

I’m so glad I decided to look further into the British Airways i360 after visiting Brighton. The story behind the structure and how innovative it is was really interesting. By seeing the i360 in person, I was able to see just how much it contrasted the rest of the town and see all of the new development happening in Brighton just nearby the i360. Since the i360 has dampers, wind loading, and live loading, I feel like everything I have learned this summer really came together for me to learn about the BAi360 in this final blog post.


References

1 http://britishairwaysi360.com/about/faqs/

2 http://www.marksbarfield.com/projects/brighton-i360/

3 https://www.istructe.org/structuralawards/2017-winners/tall-or-slender-structures/2017/british-airways-i360-at-brighton

4 https://www.theguardian.com/artanddesign/2016/aug/02/brighton-i360-review-marks-barfield-british-airways

5 https://www.theguardian.com/uk-news/2015/aug/28/its-a-bonkers-outsized-flagpole-brighton-greets-the-worlds-tallest-moving-observation-tower

6 http://britishairwaysi360.com/latest-news/the-science-behind-the-i360-tower/

7 https://www.newcivilengineer.com/technical-excellence/super-tall-super-smart-the-brighton-i360/10010065.article

8 http://britishairwaysi360.com/wp-content/uploads/2015/05/i360-Media-Pack-Updated100717-1.pdf

https://www.absolutemagazine.co.uk/absolute-news/british-airways-i360-passenger-pod-interior_credit-british-airways-i360/

10 http://www.c-mw.net/brighton-i360-seeks-global-stage/