On the morning of March 26, 2024, tragedy struck the Baltimore metropolitan area when the Francis Scott Key Bridge collapsed. The bridge, built to connect the isolated neighborhood of Hawkins Point, Baltimore to the rest of Maryland, collapsed after being struck by a large cargo ship. In this post, I will analyze everything from the failure of the ship to the failure of the bridge. However, please keep in mind the lives lost and be careful when speaking about the subject as it is both sensitive and information is still being revealed.
Background of the Bridge
The Francis Scott Key Bridge was constructed to enhance transportation across the Patapsco River, aiming to streamline commuting between the regions and facilitate the movement of cargo from a port in Baltimore. It replaced an older Aqueduct Bridge, primarily designed for canal boats rather than automobiles. As the automobile industry flourished throughout the 20th, the demand for more capable bridges grew, prompting the construction of the Francis Scott Key Memorial Bridge. This modern bridge replaced the aqueduct bridge in 1977, aligning with the era's need for improved infrastructure to accommodate increasing vehicular traffic.
This is a steel arch continuous through truss bridge. That sentence might make no sense but here is what it means. The bottom supports of the bridge are the steel arches that provide structural support to the bridge while also paying homage to the original aqueduct bridge which also had these arches. Additionally, the term "continuous" refers to these arches spanning the entire width of the bridge's lower section, ensuring its stability and integrity. The truss part of the bridge is the steel beams that connect above the central area of the bridge, as seen below. The trusses served to distribute the weight of the pressure applied to the bridge by the automobiles and other forces. They are the little triangles that you might see being interconnected spanning any given bridge. The reason they are such a unique shape is that they can distribute loads of pressure and resist multiple forces such as potentially twisting and bending. Similar to how they look, they can be viewed as the 'skeleton' of a bridge, supporting it and keeping any one part of the bridge from having too much pressure. Alongside the arches, they were meant to be able to efficiently distribute and handle the weight of all potential force, at the time. By this, I mean that in the late 20th century, this bridge was more than capable of handling reasonable loads that could be put on it. This includes ships potentially crashing into it. However, as with all other man-made objects, bridges become outdated and not suitable for modern-day use.
Why did the bridge collapse?
The bridge should not have collapsed from the collision right? As stated above, bridges should be able to withstand collisions like these, even if the force applied by the ship is very large. The reason it collapsed regardless of this is because bridges can only be future-proofed to a certain extent. While this bridge may have been able to withstand collisions of ships that were large at the time of its construction, this strength may not be sufficient for modern-day cargo. This connects back to the idea that all industries are ever-evolving and as time goes on, larger and more powerful ships will be manufactured, rendering bridges designed for the past, outdated. The bridge collapsed because it was first made to withstand a certain load, which was exceeded when the cargo ship collided with it. Before getting into the specifics, here is how something like this could have happened.
How did it happen?
it started with the ship. What is known is that it malfunctioned and the crew lost control. As of now, the potential reasons for this could be engine malfunction, electrical blackout, or simple human error. Because of this malfunction, the ship smashed into one of the central piers that connected the center of the bridge to the river bed. These piers are vital to the bridge as they quite literally hold it up.
The next question is, what's the point of using arches when other designs could hold a bridge up better? Well, when structures like bridges are designed, they are made to collapse in segments. That means that when the ship collided with the one pier, only the area around it should have collapsed. This is known as a progressive collapse. That is why arches are used. When one arch collapses, it should not lead the other parts of the bridge to follow suit.
However, the arches found on the Francis Scott Key Bridge were mainly put in place design and historical significance. Although supporting the structure, the arches were not the main way that the bridge was supported. The trusses played the largest role in this. The problem with trusses is that they are rigidly connected, meaning that if one segment fails, so does the rest. The video below shows that when one of the pillars of the arch failed, the trusses all collapsed at once. This showcases one of the most apparent downsides with the use of trusses.
A more technical analysis:
Although the trusses were implemented as a way to stop the bridge from collapsing regardless of a single part failing, the force was simply too much for the bridge to handle. Because the bridge was designed for a specific load capacity(amount of force the bridge could take), it is estimated the force applied by the ship far exceeded that. It is predicted that this force was around 30 million pounds! This video shows as soon as the cargo ship came in contact with the pier, the bridge collapsed as one. However, it also shows the trusses both failing and succeeding at its task. When watching the video, it becomes clear that the truss maintains its shape as the bridge collapses. However, the truss did not prove useful when necessary to distribute the force of the ship. This is one of the limitations at the time of this bridge being built. Although cost-effective and useful for maintaining constant forces such as average day traffic, it proves obsolete under sudden, large, forces. A more effective, but less cost-effective method, could have been suspension or Cable-stay bridges that could potentially handle this load better. However, with the bridge being built in the 70s, the cargo ships of this magnitude were not kept in mind and therefore, these bridges were not seen as necessary.
Well, what now?
Although far from common, disasters similar to this collision have most definitely occurred. Around 40 collisions of a similar magnitude have happened in the past 60 to 70 years. However, this seems to be more publicized for one vital reason. This being that there were fatalities as a result of the collision.
Now, the question is ... what should be done next time? We already have an answer to that. Actually, there are two answers. One of these is the use of a different, more suitable bridge. If the bridge used a different type of bridge design, such as a suspension or cable-stay, it may not have collapsed, or not been damaged to such an extent. The problem with this is that these types of bridges are more expensive up front and cost more to maintain. However, in the long run, they are more reliable and less likely to fail. Therefore, it could be a more cost-effective solution in the long run. Another option would be to increase the space between the end of the pier and the actual support piers by adding more material in that area. These piers can be seen below. If you look at the video of the collision, it become obvious that it has a flared bow, extending past the pier and coming into contact with the pillar. The reason it collided was because the pier's surface was not large enough to contact the ship before coming into contact with the pillar. There is a simple fix to this that could have easily prevented or mitigated the collision. By simply extending the pier's surface to cover more area around the pillar.
A Summary
The collapse of the Francis Scott Key Bridge was a tragic event that highlighted the importance of continuously assessing and updating infrastructure to meet modern demands. As we reflect on the factors contributing to this disaster, it's imperative to remember the lives lost and exercise sensitivity in discussing the incident while awaiting further information. Moving forward, lessons can be drawn from this catastrophe to prioritize the implementation of more resilient bridge designs despite their higher initial costs. Additionally, enhancing the spacing and surface area of piers can offer practical solutions to mitigate the risk of collisions and bolster the structural integrity of bridges, ultimately ensuring the safety of communities relying on these vital transportation arteries.
Thank you very much for reading and I hope you learned about how the Francis Scott Key Bridge collapsed and what we can learn from it.
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