This #seismicsaturday is riveting! We feature a 1904 railroad bridge across the Susquehanna River near Cooperstown, NY, which your Seismic Saturday correspondent spotted while canoeing.
In late 19th century and the early 20th century, when Cooperstown and surrounding areas were manufacturing hubs, the bridge was part of a bustling train route that brought raw goods up to the factories of Cooperstown, and manufactured goods back down to New York City.
The bridge looks like a modified warren truss (fig. 2). It looks to have several Warren Trusses overlain on top of one another. In contrast to the warren truss in figure 2, the Susquehanna Bridge’s design is redundant, because if one of the diagonal elements fails, the load can travel through the members of other adjacent diagonals to the base at either side. The corner joint of the bridge, shown in figure 3, is crucial in that it connects on the left with two diagonal elements and one vertical element, each of which travels downward to support a diagonal coming in from the left side.
The foundation of the bridge is made out of flat stones (fig. 4). This may be a foundation from a pre-1904 bridge, when flat river stones were commonly used as foundations (for example underneath the original white house). Stones were popular because they could be gathered from nearby. In this case, the stones were probably gathered from the adjacent riverbed. In modern bridges, river stones have been replaced with steel reinforced concrete.
See all those bumps (fig. 5, 6, 7)? Those are rivets. Riveted connections are fascinating. They are done with a cylinder with a smooth head, which is inserted into a punched hole. The cylindrical side is then smashed down to create a pin connection (see process figure 8). This type of riveting was used up till the mid 1900s, and was used to build the Golden Gate and Brooklyn bridges.
In civil structures like bridges, rivets have now been largely replaced by bolts, which are easier to install, don’t require an on-site furnace, and do better in earthquakes due to their ductility. A concern of rivets is that because they cool down so fast after taken out of the furnace, they are essentially quenched, and thus very brittle. However, riveting is still commonly used in aircraft (pic 9), and even is used on SpaceX’s 2021 Starship Rocket (pic 10). It is riveting to see technology of the past being used in structures of the future!
Note: The UC San Diego Steel Bridge Team did a 2-day Bridge Design-athon Challenge based on designing a replacement for this bridge. It includes all sorts of fun constraints, including the presence of an endangered fish species in an inlet stream. Here is a link: Bridge Designathon: Susquehanna River Bridge
Ramirez, Miguel. Doing the Math: Analysis of Forces in a Truss Bridge. Teach Engineering. https://www.teachengineering.org/lessons/view/ind-2472-analysis-forces-truss-bridge-lesson