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Passerelle Leopold Sedar Senghor

Passerelle Leopold Sedar Senghor

Structure Information

The Passerelle Leopold Sedar Senghor, a pedestrian bridge, is located on the Seine River in Paris, France. It sits between the Tuileries Gardens and the Musée d’Orsay. You can see where it is located relative to the city in Figure 1.

Figure 1. Map highlighting the location of the bridge.

It was constructed between 1997 and 1999. This bridge was built during important years. I was born in 1997, and my sister was born in 1999. The bridge standing today was built to improve the area and create a better space for tourists. The bridge was constructed as a part of the Grand Louvre project. Marc Mimram, an architect and engineer, designed the bridge. He won a competition to replace the bridge that was demolished in 1992. It was funded by the French state as a part of the project. [3] Spanning the Seine, it includes two paths that connect at mid-span, which can be seen in Figure 2.

Figure 2. The bridge spanning the Seine on a beautiful day.

 

Historical Significance

This wasn’t the first time a steel arch bridge was built, but Mimram did put a new twist on the bridge. Two paths exist on the bridge. You can climb the stairs from ground level to the top of the arch, or you can walk across the deck. This innovative design of the two walkways merging at mid-span was very important for this area in Paris to bring together the two sides of the Seine. No new construction techniques were used. Before this bridge, Mimram had only helped design a few structures. Following this bridge, he came to fame and designed many other pedestrian bridges and structures for France and many other countries. The Leopold Sedar Senghor has a striking resemblance to one of Mimram’s later bridges, over the River “La Vilaine.” In Figure 3, you can see how there are two paths on the bridge. One is on the arch and the other is on the deck, which resembles his bridge from 1999.

Figure 3. La Vilaine Bridge which resembles his earlier bridge. [1]

Cultural Significance

The first bridge built here was the Passerelle Solferino, which was inaugurated by Napoleon III in 1861. This bridge got its name from the Battle of Solferino in 1959 in which Napoleon III defeated the Austrians. [4] It was demolished because of extensive damage, and a new pedestrian footbridge was put in its place. This second temporary bridge was also demolished in 1992. The bridge standing today was renamed the Passerelle Leopold Sedar Senghor in October of 2006 to recognize Senghor, a major African intellectual during the 1900s. He was the first Senegalese president for 20 years and was a member of the Academie Francaise, so they named the bridge after him. [3] Many adored this bridge for its elegance and light design. Mimram received the Equerre d/Argent (Silver T-square), a French architecture award, for this bridge. [6] Only one of these awards is given annually, so France admired this piece of work. When the bridge was opened, ministers of culture and equipment were there, which was huge for a Parisian structure. However, two issues arose when this bridge was opened. The wood surface of the deck was slippery, and the bridge swayed, sort of like the Millennium Bridge. To fix these problems, Mimram added anti-slip strips and dampers as shock-absorbers. [5] Controversy also arose from this bridge. One piece of controversy was that the minister of culture sent the Parisian Mayor’s invitation for the opening of the bridge a little late which caused the Mayor not to come. The bridge was closed for a short time because the city did not want to accept the bridge since the Mayor didn’t show to its opening. Also, many engineers who disliked architects from the Ponts et Chaussees school, where Mimram studied, attacked his project since he worked as both an engineer and architect. A third group brought controversy over the bridge. Environmentalists said that the wood Mimram used for the bridge was endangered, but he had gone to Brazil and studied forest conservation. [6] After a few months of the bridge’s opening, all the controversy went away because many appreciated its symbolism for Paris and its lightness across the Seine. The human cost involved with this bridge only occurred during construction and fixing the deck issues. Mimram and many other builders spent a lot of their time to make sure the bridge was almost perfect for the people. Now, the bridge serves as a pedestrian footbridge across the Seine.

 

Structural Art

Following Billington’s criteria, I will first look at the efficiency of this bridge. Mimram tried to use the minimum amount of material for his bridge. It was so light that it even swayed in the wind. Therefore, Mimram attempted at using the least amount of material for his bridge, so the efficiency aspect of the bridge contributes to it being structural art. Next, I will look at the economy of the bridge. The bridge was funded by Paris, and Mimram won the project through a competition, so Paris thought that the Mimram’s design was best for the city. The bridge cost 9.8 million euro, which is a bit on the high end for pedestrian bridges, but considering this bridge has two pathways, sits in a busy area, and was built in two years, it fulfills most of the economy aspect of structural art. The last component of structural art is elegance. Just by looking at the bridge you can tell it is very elegant. The load path is clear, the bridge is very open, and the bridge is very light. Mimram wanted to make the bridge feel light and infinite. The Brazilian wood on the deck and the openness of the arch make it light and having the two paths makes the bridge feel infinite. I believe Mimram fulfilled this last aspect the most. He designed the bridge to fulfill the city’s needs, and followed the 3 E’s, so I believe this bridge is structural art.

 

Structural Analysis

Mimram became the designer for this bridge through a competition. Paris picked his design so that people would come visit this area and enjoy crossing the Seine. The arch is made of steel from the Eiffel company, which I think is really cool. [3] The abutments are made of concrete, and the deck is made of a Brazilian wood, Ipe. The foundations were built first, and they used a watertight enclosure so that they could work. The skeleton was built with supports, one of which was a pier from the older Passerelle Solferino. Builders divided the arch into 6 sections which were put together with the struts at the site of the bridge. Cranes put the large pieces together. Finally, the deck was placed on top of the arch and struts. The structural system includes two abutments (one on each side) and a steel arch with V-shaped struts that connect the deck to the arch. [7] The arch has two layers that are connected by a Vierendeel truss which doesn’t have any diagonal elements. The bridge consists of two pathways. One is at the bottom of the bridge and one is at the deck’s elevation. These two paths connect at mid-span. The live loads from pedestrians and the dead loads from the bridge’s weight are carried onto the deck and down through the V-shaped struts. The loads are then transferred as point loads onto the arch. The loads are transferred to the ground vertically and abutments horizontally, which can be seen in Figure 4.

Figure 4. Load path of the bridge.

To find the reaction forces of the bridge, I had to make some assumptions. I assumed the loads were transferred through the entire arch, not just where the V-shaped struts were. I assumed a live load for pedestrians of 90 psf. [2] I assumed an Ipe wood density of 69 lb/ft^3 and steel density of 7.85 g/cm^3. I then found the line loads associated with a bridge width of 15 m. I organized all the loads which you can see in Figure 5.

Figure 5. Load calculations.

I then found the vertical reaction forces through sum of y-components. Then, I cut the bridge in half and solved for the horizontal reaction force using the sum of the moments about the center. Since the bridge is symmetric, the horizontal forces are the same and the vertical reaction forces are the same. I then found the maximum force at the bottom of the arch. All of these calculations can be found in Figure 6.

Figure 6. Reaction forces calculations.

For this bridge, it was very important that Mimram communicate with the stakeholders about the bridge. He showed his design during the competition to communicate what the bridge would look like. He used drawings to highlight how light the bridge would be. He used the drawings to communicate with workers on the bridge as well. When the bridge swayed a little bit, he had to go back to his drawings and calculations with his workers and with authorities and show them how he fixed the resonance with dampers.

 

Personal Response

When I was in France, I passed this bridge a few times when we went to Musée d’Orsay. I initially saw someone running up the arch, and I had never seen that before. I never realized how awesome pedestrian bridges could be. The combination of the two pathways connects different groups of people like how the Seine connects two different parts of Paris. Being there made me realize that a bridge doesn’t have to be enormous to get people to fall in love with it; it needs to have a useful function and be a symbol for people who use it.

 

References

[1] http://www.mimram.com/en/?project=bridge-over-the-river-la-vilaine

[2] http://www.wsdot.wa.gov/eesc/bridge/designmemos/11-2009.pdf

[3] http://www.eutouring.com/passerelle_leopold_sedar_senghor.html

[4] https://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fparis1900.lartnouveau.com%2Fponts%2Fpasserelle_leopold_sedar_senghor.htm

[5] https://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fwww.planete-tp.com%2Fpasserelle-leopold-sedar-senghor-a96.html

[6] https://www.nytimes.com/2000/07/29/style/pont-solferinowater-under-a-troubled-bridge.html

[7] http://www.bath.ac.uk/ace/uploads/StudentProjects/Bridgeconference2011/papers/Vernet.pdf