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/

Go Arsenal! (Emirates Stadium)

Figure 1: Me in front of Emirates Stadium

Structure Information

Emirates Stadium was completed in 2006 and is located in Ashburton Grove, London [1]. The stadium is used for the Arsenal Football team’s home games. The structural engineer for the project was Buro Happold [2]. Funding for the stadium came from loans from many banks given to Arsenal Holdings plc, Granada, Nike, and sales from the land that was not needed for the stadium. Additionally, Emirates Airline paid £100 million for a 15 year sponsorship of the stadium as well as an 8 year sponsorship of team uniforms [1].


Historical Significance

A newer technique for creating steel parts was used by the steel contractor to insure the accuracy of the parts. The method included creating three-dimensional models of sections from individual X-Steel models to be used in manufacturing of the steel. The three-dimensional models could be rotated and moved in order to create the most accurate version of the parts for the stadium.  [2]

Other than this, the stadium was built as a typical football stadium, with the roof allowing sunlight to hit the field while also keep the sun or rain off of the spectators. Since the roof is not connected to the seating, there is also airflow to keep the stadium cooler without the need for air condition. What sets Emirates Stadium apart is that the stadium is an ellipse shape, rather than a rectangle, which is more common for football stadiums. [1]


Figure 2: Development at Past Stadium for Arsenal [2]

Cultural Significance

The stadium is situated inside of a 7.8 acre park, which is open to the public. Additionally, Arsenal built houses and other buildings around the stadium for the surround communities. The location of the stadium allows for access from the London Underground and helped push for improvements at the Holloway Road station and promotes politicians to obtain funding for improvements at two other stations. Arsenal also sponsored the conversion of their past stadium into apartments, student housing, a garden, and health centers. [1]

 

 


Structural Art

When looking at the roof of Emirates Stadium from inside, outside, and especially from Google Earth, the stadium, this structure displays structural art very well. The arched trusses that hold up the roof and the connection points of the roof to the elements holding the roof up are all visible and easy to find. The load paths are visible, and the structure looks light. Additionally, efficiency and economy were highly considered in the structure. Steel tubes were specifically chosen for the cost and efficiency, as well as the constructability.


Structural Analysis

The roof of Emirates Stadium is made up of polycarbonate and steel tubes [1]. Steel tubes were chosen for cost and weight purposes, as well as constructability since less surface area means less detail in the steel manufacturing process. The girders were built off-site in pieces and assembled on-site. Temporary structures were used until all of the trusses were put into place with cranes so that there was no deflection from the self-weight of the trusses. [2]

The roof consists of the polycarbonate covering and many trusses, varying in size. There is a circular truss around the perimeter, truss beams, and truss girders. Additionally, there are 8 tripod columns to stabilize and take loads. All of these parts work together to create a stadium roof that does not touch the seating area and draws the viewer’s eye to the pitch, rather than the roof [1].

The load path goes from the roof up to the smaller, triangular truss beams, up to the larger truss girders. The two secondary girders transfer the load to the two primary girders. The primary girders then transfer the load to tripod columns. A circular truss around the perimeter of the roof is attached to the roof and provides support for the beams. It also transfers load to the tripod columns, seen in Figure 3. There are also 64 props around the stadium to help transfer the load down [3]. All of the beams and girders can be seen in Figure 4, a bird’s eye view of the stadium. From the inside of the stadium, the load paths from the secondary and primary girders, as well as the columns can be seen (Figure 5). From the outside, the tripod columns can be seen connecting to the roof (Figure 6).

Figure 3: Load Path from Top View [6]

Figure 4: Tripod Column from Inside Stadium

 

 

 

 

 

 

 

 

 

 

Figure 5: Load Path from Inside Stadium

Figure 6: Load Path from Outside of Stadium

The primary girders span 204 m and the secondary girders span 100 m, with the 32 beams varying in size. The girders cross section is 15 m deep and 10 m wide. [2] The polycarbonate roof covers 27,200 m2 [4]. All of the steel on the roof weighs 3,000 tons [1]. The total weight of the roof is about 41,510,000 N [5]. This means that the average area load of the roof is 1,526 N/m2.

To idealize the roof, we can say that each beam takes the same amount of load. Figure shows the idealization schematic. The force from the roof that each beam takes is calculated by multiplying the area load by the area divided by 32. The load for each beam is:

The loads of 6 of the beams go to each secondary girder, meaning each secondary beam has 6 point loads and reactions the ends from the primary load. Due to symmetry, the reactions are equal and there are no forces in the x-dimension. Figure shows the free body diagram. The reactions are:

The loads from two reactions of the secondary girders and the loads from 10 beams are on the primary girders, seen in Figure . As with the secondary girders, there are no forces in the x-dimension and the reactions are equal. The reactions on the primary girder are:

The maximum moment in the primary girder is in the center, while the maximum shear force is right next to the reaction. Assuming the distance between the beams are all equal to 16 feet and the distance between the secondary girder and perimeter is 30 feet, the maximum moment is:

This very large maximum moment is one of the many reasons why a triangular truss in the shape of a moment diagram was chosen for the primary girders.

The design of the stadium included a huge development of the area around the stadium in addition to the stadium. Because of this, the elliptical shape was chosen since it meant that the closest residential building was over 100 meters from the stadium. Models of all of the initial designs were presented to stakeholders, and once a shape was chosen, a full model including the neighborhood was presented. [3]


Personal Response

I really enjoyed visiting Emirates Stadium. Researching it more and going into the structure was very interesting. The stadium is so massive! I didn’t even really realize at first that the roof wasn’t resting on the seating area, but when I did, I was so amazed at the structural engineering.


References

1 https://www.designbuild-network.com/projects/ashburton/

2 https://www.steelconstruction.org/design-awards/2006/commendation/the-emirates-stadium-arsenal-football-club/

3 https://issuu.com/jmurphy93/docs/dissertation_final-_emiratesstadium

4 https://www.independent.co.uk/student/magazines/emirates-stadium-new-goal-for-the-gunners-5331573.html

5 http://www-civ.eng.cam.ac.uk/cjb/schools/stadium/silcock_files/S2%20Emirates%20structural%20analysis%20Teachers%20Notes.doc

6 Google Earth

Park Drive Bridge

I found this bridge while walking in Piedmont Park this weekend to break in my hiking boots and immediately thought of how great it would be to write a blog post about. I took some pictures (shown below) and explained to my friend how we could see the load paths (which went right over his head).

Figure 1: Park Drive Bridge


Structure Information

Figure 2: Location of Park Drive Bridge [2]

Upon further research (pulling up Google Maps), I figured out the bridge was on Park Drive. The bridge is called the Park Drive Bridge, previously known as the Piedmont Park Boulevard Bridge. The structure was built in 1916 and designed by O.F. Kauffman, who was a city engineer working at the Department of Bridges and Estimates. The purpose of building this bridge was to connect neighborhoods to the park without having to walk over the railroad tracks that ran along the park, which is now the Atlanta Beltline (see map to the left). The bridge was funded by four sources: City of Atlanta, Fulton County, Southern Railway, and Northern Boulevard Park Corporation. [1]

 


Historical Significance

Since the bridge was built long after the invention of reinforced concrete and the arch bridge, there was nothing significant about the Park Drive Bridge’s design or how it was built. In fact, since the bridge is over land rather than water, it was easier to build than many of the bridges we have learned about in class so far.


Cultural Significance

Figure 3: Mural under the Park Drive Bridge [2]

This bridge previously served as a connection from the developing Druid Hills neighborhoods into the park over the railroad [1]. After the Piedmont Park parking lot was build, the bridge was used for parking lot access until the parking area for the park was moved. Now, the bridge is not open to the public for vehicles, but is still open for pedestrians and bicyclists, although there is no railroad to worry about crossing over anymore. Additionally, the Park Drive Bridge has been incorporated into the Art of the Atlanta Beltline project and features a mural.


Figure 4: Close-Up View of the Middle of Park Drive Bridge

Structural Art

 

From far away, this bridge can very well show structural art. The load paths seem clear, there doesn’t seem to be any extra beams or columns, and you can see through the bridge, as Billington commonly uses as a requirement.

Once closer to the bridge, however, you notice the tiles for decoration on the entire bridge and the heavy-looking deck with thick, ornamental bricks as a railing. You can also see small beams connecting the spandrels, which do not seem to be load-bearing given the large girders underneath the deck. These beams are most likely for decorative purposes or because the engineer was worried that the girders could not hold the entire load. This extra material and the cost to add these decorations go against the values of economy and efficiency needed for a structure to be structural art.

 

 


Structural Analysis

This bridge was built as an arch bridge in the middle and simply supported sections on the sides out of reinforced concrete. The construction was contracted to Case & Cothran and cost $28,904.75. The brick section at the top was laid and plastered after the completion of the bridge and the 7 foot deep slab. [1]

In the middle section, the longer span, an arch is in compression against two abutments. The spandrels above the arch are also in compression. There are beams connecting both arches across the bridge as well as beams running between the spandrels in line with the arches. The girders lie perpendicular to the arches and connect to the spandrels that are above the arch. These components can be seen in Figure 4.

Figure 5: Load Path on Park Drive Bridge

The load goes from the slab to the girders. These loads are then transferred to the spandrels down to the arches. The arches transfer the load to the large abutments, which finally take the load to the ground.

The load comes from both the dead load of the railings and the very small live load from the pedestrians walking across the bridge; however, there used to be a larger live load when vehicles were allowed on the bridge.

The braces connecting the arches are there for stability to make sure they do not start leaning. The beams between the spandrels are either for decoration or to provide extra support for the variable side of the girders at the edges of the deck of the bridge.

Figure 6: Full Arch Diagram

 

If the span of the bridge between the abutments is 500 ft, and the load

Figure 7: Free Body Diagram of the Left Side of the Arch

on the deck is 1000 lb/ft, the reaction forces on the abutments can be calculated, neglecting the self-weight of the structure, seen in figure 6.  The reactions in the y-directions can be found to be 250 kips.

 

 

Figure 8: Free Body Diagram of Left-Most Point of Arch

To find the reaction in the x-direction, you must split the arch in half, and find the sum of the moments about L/2 (see figure 7).

The reactions in the x-direction are towards the arch and equal 625 kips if the maximum height of the arch is assumed to be 50 ft.

To find the maximum stress of the arch, the maximum force must first be found. This is done by finding the internal compressive force at the end of the arch. A free body diagram of the edge of the arch can be seen in Figure 8. The maximum force is equal to 673.15 kips. Assuming an area of 8 square feet, the maximum stress in the arch is 84.14 kips/square foot.


Personal Response

I have walked by this bridge many times and never thought it was anything special. I think that the ornamental tiles and brick wall on top make it look like it belongs in another time period. If the bridge were cleaned up and these parts were removed, I think I would like it a lot more. Overall, I think it was very cool to see a bridge that looks similar to the sort of designs we’ve been learning about in class. Seeing this in-person, and realizing on-the-spot that I could follow the load paths, was very cool.