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The Alexandre III Bridge

The Alexandre III Bridge

I was in Paris, France just this weekend only to see how much it resembled the city of London. Don’t see how? Let me explain. If you saw my last blogpost, you know that I did a bridge tour to see about 10 bridges in line that sit on the River Thames. Well, a similar thing happened. Except this was now a boat tour. And instead of 10 bridges, I’m pretty sure I saw double the amount of bridges. But there was this one bridge that stood out to me the most: The Alexandre III Bridge. It made me want to research about it due to how elaborate and extravagant it is and was designed to be. It actually represents how I see the history of Europe to be: old, exquisite and still standing.

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Figure 1: Pont Alexandre III (Alexandre III Bridge)

Structure Information

The Alexandra III Bridge, known as Pont Alexandre III in French, is a bridge that sits across the Seine River in Paris, France. Construction of it started on October 7th, 1896 and it was completed in 1900 [2]. It was constructed to fulfill two purposes: “to celebrate the achievements of the last century” and to allow pedestrians to cross the river. To elaborate on this first purpose, there was the 1900 World Exposition that was held to celebrate achievements in fields like architecture, engineering, science and technology. This bridge along with many other structures were built to be showcased and represent Paris during this exposition. Secondly, a bridge was needed to allow visitors to cross the River Seine from the one side consisting of the Champs-Elysees to the side of the Eiffel Tower. The bridge was designed by architects, Joseph Cassien-Bernard and Gaston Cousin and it was constructed by engineers, Jean Resal and Amedee d’Albly [1]. The bridge was funded by the French government and it was named after the Russian Tsar, Alexandre III in celebration of Russian and French diplomatic relations [3].

Historical Significance

Although the focus of the bridge is its architectural work, the structural forms of its time must be recognized too. The arch hangs low to make sure that it does not block the view of the Invalides and Champs-Elysees and this was rarely done before. The bridge was also made quite slender–“tape-like proportions and wide, flat profile”. These two factors raised doubts of if the bridge would still work or even stand. To emphasize once again, these two factors–a low-hanging arch and “the slender nature of the bridge”–were rarely used or even experimented with during this time [3]. Therefore, the bridge was able to use an innovative structural engineering design that made it a structural masterpiece while it was already an architectural masterpiece.

Up until the time of the construction of the bridge, steel was used and produced using a process called open-hearth. This process involved increased temperature usage for melting metals and using the heat released as waste [4]. Also, steel was used only in small quantities because it was expensive to produce at this time. For example, steel was used when supported by brickwork and even then, “intermittent columns” were used. Speaking in regards to the connections, only simple bolting was used to join different structural members. However, with the construction of the Alexandre III Bridge, new construction techniques were used to an extensive point. The connections that were used for this bridge included bolting or riveting to join members especially in steel framed structures. Pre-cast members were made off site, shipped to the site and then bolted together on-site [1].

The Alexandre III Bridge can be characterized as a great example of work of its time for two reasons or elements: it’s structural arch that is “both simple and fluid” and its architectural decor [1]. As mentioned above, the low-lying and very fluid arch was unseen of its time, and a risky venture but it stands today as a structural masterpiece. It is also said to settle in quite well into its surroundings. Talking about the time the bridge was designed and built, it was when architecture flourished and this can be seen by the statues and facia pieces that were designed and put upon by French artists. Together with the combination of planned structural engineering and architectural work, the Bridge was a success of its time [1]. However, it does not stand as a model for future building as the heavy and elaborate decoration does not go well with the structural members that were intended to flow [1].Image result for old alexandre iii bridge

Figure 2: An old image of the Bridge

Cultural Significance

This bridge has been in use for about a century and it was built in the late 1800’s. Considering this fact and all the research I was able to do, I was not able to find the impact the bridge had on lives–both living and dead. As for those who lived at the site of the bridge, that is not applicable as the bridge was built on tourist/visiting areas to allow pedestrian traffic to flow across the bridge.

The bridge was constructed at a time that reflected the strength of France-Russian relations. This can be seen to have an impact on the bridge: “the first stone..[of the bridge]..was laid in 1896 by Tsar Nicolas II of Russia and the bridge was dedicated to his father Alexandre III” [1]. One of the decorative features of the bridge also reflects this alliance. The Nymph of the Seine and Neva rest on the keystone which represents the relationship between Paris and Russia. Built to be showcased at the World Exposition of 1900, the bridge served to represent Paris and its accomplishments in architecture which could be seen from the varying ornamental decor on the bridge [7].

The impact of the bridge is not limited to history; we can see it appear in pop culture–particularly films. The bridge has appeared in the last scene of the 2011 movie, Midnight in Paris [5]. It has made appearances in multiple other movies like Anastasia, Ronin, A Very Long Engagement, and A View to Kill. This reference is my favorite–the bridge has appeared in the background of Adele’s video of the song, “Someone Like You” which I have yet to notice [6]!

Although the behavior of the tourists and visitors of the bridge aren’t clear as to either being loving towards it or absolutely hating it, most people like or at least admire the bridge for its grandeur. Also considering that the bridge was designed to allow 50 million people to cross it, the bridge rose from a need or a purpose which would not allow hate to flourish [1].

This bridge is still used as a pedestrian walkway connecting opposite sides of the Seine River to each other. It allows tourists to visit both popular areas–the Champs-Elysees commercial area to Les Invalides–by just crossing the walkway. Till this day, the Alexandre III Bridge is known as “one of the most elegant and artistic bridges in the French capital” [3].

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Figure 3: Sketch of the Aleaxandre III Bridge

Structural Art

Although this bridge can be characterized by me as art, I would not consider this bridge as structural art. I have made this judgment based off of David Billington’s criterion of the 3 E’s.

Firstly, looking at the economy of this bridge, I was not able to find any values representing the cost of the construction. Nonetheless, an assumption can be made by looking at the grandeur of this bridge that it was quite expensive especially considering all the artwork that was put into place. Therefore, the bridge is not very economical.

Secondly, looking at the efficiency of the bridge, minimum amount of material was not used. Although the arch is smooth and low, it creates larger horizontal forces for which large abutments and foundations had to be put in place [1]. This takes away from the whole idea of structural art as one part of the bridge is smooth and minimal while the other part takes up the consequences (notably the abutments). Therefore, the bridge is not efficient.

Lastly, we talk about elegance which is more of an opinion. I do agree that the arch of the bridge is smooth and fluid, the load path can be easily seen and it has used methods that were not seen previously. However, as soon as my eyes move past the arch to the deck, I see these huge architectural pieces that I personally don’t think belong on a bridge. Instead of making it look grand and exquisite, it makes it look heavy and unnecessary. Therefore, this bridge is not elegant either!

In conclusion, the Alexandre III Bridge fails to pass the structural art test of the 3 E’s developed by Billington and used by me–so, it’s definitely not structural art!

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Figure 4: Alexandre III Bridge with Eiffel Tower in background

Structural Analysis

Although the bridge is analyzed from a structural engineering perspective, I still think it’s necessary to talk about the architectural pieces that sit on the bridge. There are two pillars on each side of the bank that stand at a height of 17 meters that act as counterweights for the arch. In front of each pillar, there is a female statue. On top of each pillar, there is a golden statue of Renommee, the Fame restraining Pegasus. There are also hammered copper sculptures at the keystones. Across the bridge, there are 32 candelabras, or lamp posts that light up the bridge [9].

Figure 5: The decorative pillar shown above and the candelabra shown beneath it.

The bridge is a three-hinged arch bridge with a total length of 16o meters. The main span that makes up the only and largest arch is 107.5 meters in length. The width of the deck is 40 meters [2]. The deck is so wide that it encompasses three traffic lanes of each direction, bike lanes, and sidewalks. The arch itself is composed of steel [3]. There are two masonry viaducts that sit at each bank on both sides. Since the arch hangs very low, it creates large forces that must be resisted by large abutment foundations [7]. Pneumatic caissons made of steel were put into place [1]. This is just an overall idea to build the picture of the bridge in your head–more details to come below!

At this time, mainly wrought or cast iron was used to construct large structures. However, this bridge was able to use mass quantities of steel due to the open-hearth process. The steel components were made in a French factory, Le Creusot. The caisson itself was made of steel  and its walls were composed of corrugated steel plates [1]. The girders are made of cast steel. Masonry was used for the side viaducts [7].

The bridge sees extensive use of wholly steel-framed structures that are made of bolted or riveted arrangement of members. Members were pre-cast off site and then brought on side to the River Seine to be bolted on parts of the bridges [1].

Now, we talk specifically about some of the structural systems put into place that allow the bridge to function as it does. Firstly, the arch stands at a height that is 1/17 to its length which is very low to the standards of that time. This steel arch is supported by bracing members. There are also 15 arch ribs that are arranged in a parallel manner in the front and back side of the bridge. Underneath the bridge, there is a complex array of braced-trussed structures as can be seen in the image below. As the arch is a 3 hinged arch, it must be recognized where each of the 3 hinges are: one at each abutment and the 3rd one at the apex, or the highest point of the bridge.Steel Structure

Figure 5: Steel bracing structure below the bridge

 

 

Figure 6: Parallel Ribs and Foundation at Right Edge of Span

Now, talking about the foundation, pneumatic caissons of heavy weight with open tops and bottoms were sunk and then used as abutment foundations of the bridge. Two masonry viaducts are put on each side of the arch at the banks that can be considered as part of the foundation to resist the thrust forces from the arch [1].

The load path of this bridge can be simplified to include the dead and live loads of the weight of the bridge, other structural and architectural members, occupancy and weather loads. This combined load is acting on the deck, downwards. From the deck, it gets transferred to the 15 parallel ribs that seem to hold up the deck in a stiff position. It is transferred in response to its tributary area from the deck. From there, the loads are transferred to the arch which is in compression. The loads that are being transferred from the deck have horizontal and vertical components. The vertical components are transferred from the arch to the foundation on either side of the arch then into the ground. The horizontal components from both the arch and each viaduct(because each viaduct is shaped like an arch which thicker ends but act as arches) are transferred to the abutments.

Figure 7: Load Path of Bridge

In the analysis of the central span, some assumptions and idealizations are made. Firstly, AASHTO Specifications were looked at to see the dead loads that could be applicable for this bridge. The dead load unit weight that is used for steel is 490 lb/ft^3 [8]. This measurement was multiplied by the width of the bridge, 131 feet, to get a load per linear feet. Although this load and the values seem quite high, it works out at the end because of the extensive architectural pieces resting on the bridge. In that case, the uniform load cannot be characterized as just dead loads.

Figure 8: Free Body Diagram of Middle Span with uniform load

Figure 9: Calculations to find Vertical Reactions

Figure 10: Cut made at middle hinge

Figure 11: Calculations for horizontal reactions or thrusts

The vertical calculations found in the image above are the loads that are transferred into the foundations at the ends of the span. The horizontal reactions are the thrusts that are developed from the compressing of the arch and they are transferred to the abutments.

Another analysis will be made about the stress experienced by the deck: this is applicable regardless if the load assumptions stated above are not true. The deck experiences heavy loading or forces and therefore will experience high amounts of stress. Therefore, from the stress equation (sigma/stress = force/area), it is reasonable to see what area of the deck is needed to maintain an allowable amount of stress under the force it experiences.

Since this bridge was built at an earlier time, the designers/architects and engineers were able to communicate the image they had in mind for this bridge through drawings. This allowed them to build the bridge in 2 years [7]. These drawings and drawn models were necessary to convince the French government that the bridge is in fact low enough to not obstruct Les Invalides as this was the main requirement by the government [3].

Personal Response

By actually traveling on the boat underneath this bridge, I realized how much more exquisite it is in person. No seriously, it seemed like I was in an outdoor museum! I also realized how heavy those architectural members must have been. But, it is this bridge that gives Paris its historical and expensive feel! It makes me realize that some structures aren’t built for engineering purposes but rather for the city’s name and honor as Pont Alexandre III has been built for Paris. Nonetheless, we reflect on these structures and take the best from them–such as the low-lying arch from this bridge!

References:

[1] http://www.bath.ac.uk/ace/uploads/StudentProjects/Bridgeconference2009/Papers/STEPHENSON.pdf

[2] https://structurae.net/structures/alexandre-iii-bridge

[3] https://study.com/academy/lesson/pont-alexandre-iii-bridge-history-statues-facts.html

[4] https://www.britannica.com/technology/open-hearth-process

[5] https://www.cntraveler.com/galleries/2014-10-31/11-filming-locations-paris-you-can-visit

[6] http://www.parisprovencevangogh.com/paris/pont-alexandre-iii-%E2%80%93-the-most-spectacular-bridge-in-paris

[7] https://web.archive.org/web/20061125232017/http://www.v1.paris.fr/en/Visiting/SITE.ASP?SITE=10007

[8] https://www.inti.gob.ar/cirsoc/pdf/puentes_hormigon/25-Lecture06-Design%20loads.pdf

[9] https://www.travelfranceonline.com/pont-alexandre-iii-a-lavish-decoration/

Comments

  1. kunangst3 says

    This bridge also caught my attention when we were in Paris. I never would have guessed that this bridge was built at the same time as the Gare d’Orsay (now Musee d’Orsay)! It seems that the towers on the ends are just for decoration. Do you know what the gold figures on top of the towers are and why they are there?

  2. skyrazis3 says

    I am on the same page about the immediate draw of this bridge. It is so ornate it is hard not to be drawn to it and wonder about its history and why it is there. What I thought was so neat about this bridge when we passed under it was the use of the gold ornament to emphasize the center hinge of the arches. Even though this bridge may not be structural art because it does not align with David Billington’s criteria, I thought it was really interesting that emphasis would be put on the structural system through ornament.