Blog 2
Chelsea Bridge

Chelsea Bridge

Of the 30-some odd bridges that cross the River Thames, many people, including me are probably wondering why the Chelsea Bridge is at all different or special. Most of the bridges have been there a long time and some look similar. There haven’t been any huge scandals involving the bridge since it was the original bridge that stood in the same place a long time ago. However, this bridge is unique, at least to the structural engineers out there. It’s especially unique to the structural engineering Brits, as the Chelsea Bridge was the first of its kind in the U.K. and still is one of the only ones in the country like this.

As someone new to the country and only being here for a short while, I don’t have any fun anecdotes to share about the Chelsea Bridge; pity. But, I think the Chelsea Bridge speaks for itself and anyone who cares about bridges would be interested in this bridge’s history and I don’t know about you, but looking at any bridge I can’t help but ask myself: “how the hell does it stand up like that?” I guess we’re going to find out.

 

Structure Information

 

Name: Chelsea Bridge

Location: London, United Kingdom

Figure 1: The Chelsea Bridge at Night [1]

Figure 2: Satellite Image of Bridge Location

Construction Start Date: 1935

Bridge Opening Date: May 6, 1937

Main Span: 352’

Side Span (2 of them): 173’

Width: 64’

Total Length: 698’

Budget: £365,000 (approximately $486,300 with 1937 conversion rate)

Budget (2017 equivalent): £ 22.4 million (approximately $29.8 million with 2017 conversion rate)

Designers: E.J. Buckton and H.J. Fereday of Rendel, Palmer & Tritton

General Contractor: Holloway Brothers

Steelwork Subcontractor: Furness Shipbuilding

Cables Subcontractor: Wright’s Ropes Ltd.

Fun fact (maybe not fun, but relevant): The construction finished 5 months ahead of schedule

[3]

 

Structural Elements and Materials

  • Towers – steel
    • Sit on rocker bearings

Figure 3: Chelsea Bridge Pylons

  • Cables – steel
    • Comprised of 37 strands of high tensile strength wires
    • Each wire has an 1 7/8 ” diameter
    • Hexagonal
    • Self-Anchored

Figure 4: Cables and Self-Anchors

  • Foundations – steel sheets
    • Cofferdams

Figure 5: Rocker Bearings Under Piers

 

  • Piers – concrete encased in granite

The Chelsea Bridge I am discussing in this blog is actually the second of the Chelsea Bridges. The first one was built to connect the densely populated north side of River Thames to the new (at the time) open green space, Battersea Park. The current bridge replaced that bridge to deal with the high traffic volumes that doubled in the time from the beginning of the 1900s to 1929.

 

Historical Significance

The Chelsea Bridge was the most significant suspension bridge built in Great Britain in between World War I and II. Being the first ever self-anchored suspension bridge (meaning it balances itself) in the country, its erection signified a new era of British bridge engineering. Despite the U.S. having already achieved this bridge form multiple times, Britain was recovering from the Great War and by this time had fallen a bit behind other engineering world leaders. Nonetheless, this type of bridge was perfect for its location because soil in London is more of a clay, and not very easy to stabilize a bridge with. As a self-anchoring suspension bridge, the cables anchored to the deck, rather than the clay which made the whole structure more stable and strong while also being innovative. Even cooler, the old Chelsea Bridge’s abutments were left and strengthened when the rest of the bridge was demolished, and the new bridge rests upon them bringing the past into the future (sorry for the cheesiness but, come on. That’s cool.) However, it is important to note that while the abutments were the major stabilizing and strengthening support for the Old Chelsea Bridge, they are entirely secondary to the new.

 

Despite being innovative in its location and in its time, only one other bridge in the U.K., built in 2011 is a self-anchored suspension bridge. Chelsea Bridge may have been significant in regards to the past, but historically it did not serve as a trendsetter when looking ahead all the way into 2018. Furthermore, the United States had already started mastering the form of self-anchoring by the time the Chelsea Bridge was built, so the Chelsea Bridge may be the best example of its kind in the country, it is not in the world. Perhaps this is due to the difficulty in constructing self-anchored suspension bridges because normally the suspenders would be able to serve as temporary supports for the deck during assembly. Since the cables have to connect to the deck, this method doesn’t work, meaning a lot more money must be spent on constructing temporary falsework until the system can work as a whole.

 

Cultural Significance

 

The Chelsea Bridge holds massive amounts of cultural significance. The original bridge was meant to connect Battersea to the rest of London, but also serve as a bridge for the lower class to connect to the upper classes. But, the bridge’s history predates even the original bridge: during construction in the mid-1850’s, many Roman artifacts were unearthed (literally). Researchers now believe that Julius Caesar crossed River Thames at this same point in 54BC. A Celtic Battersea Shield, one of their most famous and coveted pieces of military equipment was also found at the site. To be honest, I don’t know much about either of these things and I might be nerdy, but not so much for history. But, crossing over the River Thames at the exact same place Julius Caesar once did is almost unfathomable to me; I honestly can’t describe what that even represents, so I’m not even going to try and describe it. I will just move on and let that sit.

 

Much more recently (of course relatively) Queen Victoria opened the Victoria bridge in her name and walked across it for the first time in 1858. Of course, once the bridge started showing significant failures and people worried it might collapse, she ordered for the name to be changed to Chelsea Bridge so as not to associate any negative connotation to her name. I mean, she named the bridge after herself and then un-named it because she wanted to only be seen as perfect. I am legitimately rolling my eyes right now. Anyway, the original Bridge was taken down. Adding even more to controversy, the bridge was meant to better connect the lower and upper classes, but crossers had to pay tolls to pass over it. Finally, along with all the other bridges in London, the tolls were removed by an act of Parliament and people started using the bridge again.

 

Moving forward to the new bridge, the current Chelsea Bridge, many cultural events demonstrated not only its local significance but also its national and international importance. The bridge opening was in the news (you can watch the original news reel below attached below) and the Prime Minister of Canada was the one who cut the ribbon ceremonially to cross over the bridge with King George VI. The bridge is made of materials all sourced from within the U.K., or at least its territories, to stimulate the economy.

The bridge, though originally hated for its tolls and basic inadequacy (it couldn’t even be crossed once the sun went down because it didn’t have any street lamps), Chelsea Bridge is well received today. It still stands as a road and pedestrian bridge. Chelsea Bridge has also passed with no drama since the original bridge – Queen Elizabeth II hasn’t tried to name it after herself since its success – and has represented positive engineering progress, especially in the time during the two World Wars when London clung to everything that could be positively symbolic.

 

Structural Art

 

When considering the 3 E’s, efficiency, economy, and elegance, we have to consider both what the bridge serves as and stands for now and in the past, but also what the bridge was meant to represent when in the design and construction phases. However, since we are now into the 20th century, we are moving more towards company collaborations between architect and structural artist, and the exact intentions become more obscure in all the data provided for these bridges. Chelsea Bridge is decades old, but when comparing to bridges built a century or two ago, even when comparing to some of the other bridges crossing River Thames, Chelsea Bridge is young. Consequently, not as much time or analysis has been done in regards to its building or its overall impact. Whereas I can say Roebling was known for the Brooklyn Bridge and his cables as well as his overall understanding of structures as an art, or Telford cared immensely for all the E’s, not enough has been unearthed about the intentions or techniques of the specific designer, but rather to the technology as a whole. As a result, I will analyze and compare this bridge as structural art from my own lens, looking at what it is and represents now that it is built. This is valid analysis because thinking back to the Amann and the George Washington Bridge, the final product of the Iron Skeleton that the bridge is notorious for now was never the intention of Amann in the first place, yet the bridge still stands as one of the most beautiful and ideal examples of structural art in my opinion. So, with that in my mind, and being the perfectionist (or so I like to think) that I am, I have provided a pros and cons list to really simplify my analysis as much as possible, despite my realizing that it just takes me one step further on the nerd scale.

 

Efficiency

Pros:

Chelsea Bridge as a self-anchoring suspension bridge saved material and effort.

  • By not trying to tear down or restoring the old abutments that were used unsuccessfully for the first Chelsea Bridge, but rather letting the deck rest on them as an added precaution, material and effort was saved.
  • Workers did not have to demolish the old abutments and then start from scratch and use extra material to stabilize the bridge in the unstable clay soil.
  • A brand new bridge was made with less hassle and was innovative in its design so that it could essentially hold itself up.

Cons:

  • The concrete, was covered in granite for aesthetic effect, which was entirely unnecessary to the structure.
  • Construction required more materials and effort including an independent pedestrian bridge to allow crossing during construction.

Considering all factors in terms of efficiency, the overall finished product of Chelsea Bridge is efficient, the construction was not necessarily. I am deciding this because even though Granite is used inefficiently, the load path is still clear to the viewer and there are very few ornamental elements besides some lamp posts that are there for architectural rather than structural purpose. To learn more about the old bridge and the construction of the new, see the newsreel by News in a Nutshell on the topic:

Economy

Pros:

  • The bridge has had no failures since its erection, meaning relatively low maintenance costs.
  • Saved money by not completely erasing the old bridge and starting from scratch.
  • Only used materials from within the commonwealth of Great Britain.
  • Generated work within the commonwealth during the time in between the wars.

Cons:

  • An entire temporary bridge was built to accommodate the construction of the Chelsea Bridge.
  • Granite cost was unnecessary.
  • Since the bridge is toll-free, it doesn’t generate any revenue itself.

When weighing the pros and cons, I conclude that since economy is inherently tied into efficiency, and since the bridge has lasted so long without significant damages or issues, the Chelsea Bridge is economical. Furthermore, the bridge helped Britain’s economy in general by only using materials from within its jurisdiction, which sort of counterweighs the negative effect of additional material and lack of direct revenue generation.

Elegance

Pros:

  • Small pylons
  • Self-anchored allows for no large abutments
  • Clear load path
  • Relatively few ornamental and unnecessary flourishes

Cons:

  • Painted to represent national pride, but in my opinion takes away from the look of the steel (again, I love the GW Bridge so I’m a bit biased).
  • Granite obscures the steel piers above the water line
  • Lamp posts are ornamental in their composition and take away from the sight of the bridge as a system

Overall, the new Chelsea Bridge in my opinion achieves the label of structural art. I cannot say much about the intentions, but I believe the bridge is in fact elegant when compared especially with some of the other bridges across River Thames such as Tower Bridge which is mainly ornamental. This bridge stands for the purpose of standing while also fulfilling social and symbolic missions such as connection the classes in the neighborhoods surrounding the bridge and aiming for elegance, efficiency, and economy.

Structural Analysis

As previously stated, though probably not adeptly explained, Chelsea Bridge is a self-anchored suspension bridge constructed of steel. It has two towers, each containing two pylons, that transfer the load from the cables to the foundations. The cables connect the main span of the bridge to the deck of the side spans, right above the abutments from the last bridge. This means that the deck counteracts the tensile forces of the cables that point towards the center of the bridge rather than the abutments. The load path and free body diagrams are shown below in figures 5 and 6 respectively.

Figure 6: Load Path

Figure 7: Simplified Free Body Diagram of Entire Structure

 

Load calculations:

Material weights:

Steel: 490 lb/ft^3

Reinforced Concrete: 150 lb/ft^3

Assume Live Load factor is .8: LL = .8*DL

Structural Element Weights:

Pylons (x4):

Hp= 69.2’

Assume square cross section with side length of pylons, Sp = 1.5’

So, weight of pylons, Wp=4*((1.5ft)^2)*69.2ft*.490k/ft^3=305.2kips

Cables:

Based on common values for high tensile strength cable properties, WC =3.97 kips/698’ = .006k/ft

Deck:

L = 698’

wD = 68’

Assume cross sectional area AD=.75’*68’=61sqft.

WD = 150lb/ft^3*51ft^2/1000lb=7.65k/ft

DL = ((7.65+.006)k/ft * 698’ + 305.2k)/698’ = 8.09k/ft

Therefore, the total load W = DL + .8DL = 14.57k/ft

Using equilibrium to solve for the reactions we can take the following steps:

Figure 8: Solving for Vertical Reactions

Figure 9: Continue Calculations

Figure 10: Calculations Continued

Now try and picture this: if you make a new cut and look at the bridge from one of the piers to the anchor on its respective side, then you find that Ax = Cx =Bx = Dx = 17325.16kip. Otherwise, the pylons and anchors would not be in equilibrium and everyone would be watching the pylons tumble down all dramatically.

Figure 11: Continued Calculations

To find the maximum and minimum tensile forces in the main and side spans, we can use Pythagorean theorem and sum of moments:

Tmain,max= sqrt(“(8662.58kip)^2 + (2564.32 kips)^2) = 9034 kips”

Tside,max = sqrt(“(8662.58kip)^2 + (5142.26 kip)^2) “=10074 kips

Figure 12: Final Calculations

Unfortunately, there is not much information on the original drawings and plans of the Chelsea Bridge or how they were disseminated to the public to increase engagement. My guess would be that the public did not have access to the bridge plans, but that they were passed around among the team, which was quite large. Similarly, since there is not much information on the funder of the bridge, it’s unclear whether or not they would’ve been able to understand and use the drawings to inform their decisions. However, considering there were so many subcontractors and parties involved, the drawings would have to be pretty legible and easy to read, otherwise everyone would’ve have fought and there is no way (I mean seriously, imagine if they couldn’t communicate because of bad handwriting) Chelsea Bridge could have been finished 5 months ahead of schedule. I mean, when my family tries to do a group gift at Hanukkah time, we have trouble communicating and that’s just looking at emails and different sites, never mind that my older siblings complain that I text in “hip” lingo that they can’t understand. So, imagine that on a huge scale with absolutely no room for error; I’d say the drawings were both made and utilized pretty successfully.

Personal Response

At first glance, the Chelsea Bridge didn’t seem all that special to me. However, the history of it, the fact that while self-anchored bridges are uncommon in the area attracted me to it. Plus, I can’t help but laugh about the fact that the Queen changed the name of the bridge so she wouldn’t have any negative connotations. Like, I’m pretty sure that the British Monarchy has been battling many haters, especially Queen Victoria who was surrounded by scandal. And yet, an unsuccessful bridge can’t be associated with the royal family. Anyway, the colors catch my eye and the idea that the bridge balances itself really amazes me.

References

  1. http://www.job32v8.com/_2/?p=293
  2. https://londonist.com/london/features/secrets-of-chelsea-bridge
  3. https://historicengland.org.uk/listing/the-list/list-entry/1393009
  4. https://www.greatlondonlandmarks.com/place/chelsea-bridge/
  5. http://web.engr.uky.edu/~gebland/CE%20382/CE%20382%20Four%20Slides%20per%20Page/L2%20-%20%20Loads.pdf
  6. https://www.youtube.com/watch?v=uHEtLvHeaOE
  7. https://www.youtube.com/watch?v=mmAo9Ft8xHw
  8. https://www.britishpathe.com/video/chelsea-bridge-news-in-a-nutshell/query/Bridge
  9. https://www.bristol.ac.uk/civilengineering/bridges/Pages/NotableBridges/Chelsea.html
  10. http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=53