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Winston W, Architecture
When gazing down the Hall of Fame of Architecture, each distinct building glints with both creativity and functionality, from the likes of I.M. Pei to ancient masterpieces like the Colosseum. These are admirable outcomes of humanity’s study of design, but how would one feel walking down the hall of shame in Architecture? Flawed construction, outrageous contemporary designs, and collapses come together as solemn admonishments for the dangers of overambitious projects or misunderstanding the fundamentals of architecture and construction. One such is the infamous Tacoma Narrows Bridge Collapse, which marked its place in architectural history.
The Tacoma Narrows Bridge, built in 1940, was a classic suspension bridge connecting the Olympic Peninsula with the mainland of Washington state. The bridge collapsed due to 67 km/h winds four months after its opening (Britannica, 2021).
A Lens into Bridges in Architecture
Bridges are some of the most fascinating structures found and studied in architecture and engineering. The usual aspects bridge engineers consider include the load's Type and weight (passenger vehicles, pedestrians, etc.) and how the deck will transfer the weight of the load. Due to the nature of bridges carrying load, the forces each component experiences would be tension or compression, which are concepts that directly influence the design and justification of bridges. Here are some of the most essential types of bridges:
1 - Suspension Bridge
Suspension bridges have high towers connected by thick, draping steel cables with thinner vertical extensions that support the deck load. As a car drives on the bridge, the deck bends downwards, experiencing compression and tension. The cables that help transfer this weight to the towers need to be highly reliable, as all of the tension from the cables needs to be canceled out with the towers’ compression. The main benefit of a suspension bridge is that it is more flexible than concrete-based bridges so that it can withstand natural disasters more easily.
2 - Cable Stayed Bridge
Cable Stayed Bridges are highly similar to Suspension bridges in their use of towers and cables to support the overall structure. Instead of having two large draping cables extending from the tip of each tower, the Cable Stayed Bridge’s cables directly connect the deck to the tip of the towers. Cables tense as they get pulled, in which the tension is balanced with the compression force of the towers. Cable Stayed Bridges are effective because they allow each section of the bridge to act as a counterweight for the other sections, making it remain in equilibrium, which is helpful for long and tall bridges that require a blend of stability and flexibility. They are also cheaper than Suspension Bridges.
Suspension and Cable-stayed bridges can be used in conjunction, as seen in the Brooklyn Bridge.
3 - Arch Bridges
Arch Bridges are some of the most well-known and strong bridges dating back to ancient civilizations, mainly because they can be built from pure stone. Two types of arch bridges are spandrel arch bridges (deck above arches) and through arch bridges that are more modern(deck below arches).
The most important part of an arch bridge is the keystone in the center of the arch that supports the two curves to its side and acts as an equilibrium for the transfers of forces.
4 - Truss Bridges
Truss Bridges are different from the rest. The triangular shapes increase the overall strength and ensure that each truss experiences only one type of force (compression or tension) that helps the bridge balance the weight load on the deck. These bridges are typically extremely stiff, which makes them strong against winds, and can be constructed quickly due to the various shapes Truss Bridges can assume.
5 - Cantilever Bridges
Cantilever Bridges take slightly different approaches to Truss Bridges, where steel cables extend above and beneath the deck. If the middle sections are strong enough, the bridge can endure tension from above the deck and compression from below the deck. What is remarkable about Cantilever bridges is that the deck is not directly secured by pillars underneath. Steel is widely used because it is durable and can withstand compression and tension forces much better than other metals. (WIRED, 2020).
The project and why it failed
Based on the investigation into bridges in Architecture above, we can tell that the Tacoma Narrows Bridge was a suspension bridge. Suspension bridges are flexible, so they are naturally more resilient structures. However, due to the extreme length and narrow construct of the Tacoma Narrows Bridge, before it collapsed, it had already been observed to sway significantly under mediocrely windy conditions. The post-collapse investigation into the causation of the incident suggested that the Bridge was fundamentally aerodynamically unstable along the transverse (perpendicular) direction to the oscillations.
Apart from this, a physics phenomenon known as aeroelastic flutter was also a primary cause of this disaster. Usually, bridges allow air to pass through the structure, which the Tacoma Bridge Design could not accomplish due to its solid sides, which resulted in flow separation that restricted its ability to withstand winds. (Harish, A., 2018).
Reference List:
Britannica (2021). Tacoma Narrows Bridge | Collapse, Disaster, Length, History, & Facts. [online] Encyclopedia Britannica. Available at: https://www.britannica.com/topic/Tacoma-Narrows-Bridge.
Harish, A. (2018). Why the Tacoma Narrows Bridge Collapsed. [online] SimScale. Available at: https://www.simscale.com/blog/tacoma-narrows-bridge-collapse/.
Scotland's Oldest Bridges (2024). Parts of a bridge and gloss. [online] scotlandsoldestbridges.co.uk. Available at: https://scotlandsoldestbridges.co.uk/parts-of-a-bridge-and-gloss.html.
WIRED (2020). Every Bridge For Every Situation, Explained By an Engineer | A World of Difference | WIRED. YouTube. Available at: https://www.youtube.com/watch?v=1bUnFjMOrPs.
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