Update 2: Suspension/Rope/Cable Stay Bridges

So I decided to further narrow down my research to fit the topic of tensile structures; which includes Suspension and Rope Bridges.

Basic Structure and Physics

The image above depicts all the components of a suspension bridge that are either in compression or tension. The diagram shows the physics of why suspension bridges stay standing. The cables and suspenders that are in tension are integral in sustaining the decks camber, and transfer the weight and load of the deck to the towers. The towers then take the weight that are passed on to it from the cables and deck and direct that force into the ground and keep the bridge raised. The anchorages and cables on the outsides of the towers play important roles as well. When the towers are loaded with the weight from the cables and deck in the center, they naturally want to fall inward. The outer cables and anchorages help to counteract that force and keep the towers under pure compression, as well as carry the load of the short segments of deck on the outside of the towers. Due to the nature of suspension bridge elements being in either pure compression or tension, these elements can be very slender, creating elegant forms.
This diagram helps depict details of the force diagram, specifically the forces acting on
the anchor block, and the connection of the cables to the tower.
Suspension Rope Bridges

Many modern rope bridges today operate with similar physics to that of suspension bridges, and borrow many of the suspension bridges’ components, such as; the Weight Bearing Tower, Anchoring Cables, and Anchoring Points. Using these elements allows the rope bridge to be lighter, stronger, and easier to assemble. Below are a few pictures demonstrating the qualities as mentioned above.
Some interesting suspension bridges to consider:
Suspension Bridge Materials

Suspension Bridges can use a wide range of materials for a variety of purposes. Some of the earlier suspension bridges didn’t actually use steel cables in the tension components, but actually used steel beams pancaked together and strung between towers such as the Clifton Suspension Bridge above. The more modern practice used today is steel cables woven together with hundreds of steel fibers to create a single cable. This method keeps it’s strength even if a few of the fibers within the cable are flawed. Whereas with the earlier beam method, one bad beam could bring down the entire bridge.

Cable Stayed Bridges

Cable stayed bridges share a certain similarity between suspension bridges, but they are drastically different. The main structure of suspension bridges as mentioned above are primarily the anchor blocks and towers. Whereas cable stayed bridges rely entirely on the towers and have no need for anchoring blocks. Cable stayed bridges can range from one tower to support the entire bridge, to multiple towers in line to support a continuous deck.

Cable stayed bridges enable the designer to have quite a bit more leeway in deciding how a bridge is laid out.  Using a cable stayed bridge platform allows for the bridge to curve, due to the focal point where all the cables attach.  Cable stayed bridges also allow the designer to take liberties to redefine the space of the bridge through the varied use and location of cables. Below are a few examples demonstrating some of the available methods of using cable stayed bridges.

Hybrids that combine suspension and cable stayed bridge elements are interesting compositions that take multiple traits of either category and combine a variety of unique bridges. One such bridge is the Brooklyn Bridge.

Above is a link to my full sized presentation poster from the Sep 8th presentation.


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