Railway bridges are an incredible feat of engineering. The railway bridge types themselves are composed of basic materials, such as concrete, metals, and stone. They seem fairly simplistic, however depending on the railway bridge types, they are able to support thousands of pounds of material, moving at extremely high speeds.
To give you a better idea of the railway bridge types, we’ve put together an overview:
Four Common Types of Bridges
- Arch bridge
You would assume that most of the support for a railroad bridge would come from its foundation, since gravity and all that jazz, however what makes an arch bridge strong is the support above it (although some arch bridges also have the arch underneath the deck as well. This increases support and offers an aesthetic element).
Unlike the other railway bridge types that we’ll talk about today, the arch bridge is anything other than a new idea. In fact, using an arch for structural support dates back to Etruscan-era, a civilization that existed prior to the Romans. The earliest known arch bridge is the Pons Fabricius that was built in Rome in 62 B.C..
So what makes an arch bridge so strong? Arch bridges are built of wedge pieces that are formed together to create the arch shape. With other structures, gravity pulls the weight of the object downward, which puts the entire burden of the railroad on the deck and the support beams. Instead, the wedge shapes press into each other and distribute the weight towards that abutments. The more weight the arch bridge is supporting, the more the weight is distributed. This makes arch bridges extremely strong.
Arch Bridges You May Recognize: The Sydney Harbor Bridge in Australia is an arch bridge. As we mentioned, the Pont Du Gard bridge in Rome is an arch bridge.
- Truss Bridge.
This brings us to one of the most common railway bridge types out there. A truss bridge is created with a series of beams that are in a triangular shape. The triangles are added in series to absorb and distribute the weight throughout the bridge. Some bridges have a single truss, and some bridges are built with a double truss system, that adds a little more support to the structure. Since the trusses are the element to a truss bridge that does the heavy lifting, it must be made of an extremely strong material, like steel.
Truss Bridges You May Recognize: Although many of the most recognizable truss bridges are combined with other bridge designs, the Tokyo Gate Bridge in Japan is a classic example of a straight-forward truss bridge.
- Suspension Bridge
Ah, yes. A suspension bridge. Just like suspenders hold your pants up, a suspension bridge is supported by a cable that holds the deck of the bridge up with suspenders. The center of each cable arches downward in the middle, so the suspenders in the center of the suspender bridge are shorter than the suspenders closer the the support beams.
The suspension bridge offers great support over a long distance, since the strength of the bridge is renewed at each vertical beam. It also offers aesthetic value, as the suspension bridge appearance is pleasing to look at.
Suspension Bridges You May Recognize: Many extremely iconic bridges across the United States are suspension bridges. The Golden Gate bridge in San Francisco is a suspension bridge with some truss and girder elements. But the tale-tell suspension cables make it easy to recognize.
Girder bridges are fairly straight-forward in design. There are a series of abutments that hold the railroad bridge up, and the girders below the deck to distribute the weight of the railroad. Since it’s the girder that’s doing all of the work for the bridge, it has to be made of an extremely durable material and designed in such a way to withstand massive amounts of pressure. Girders are categorized as rolled steel girders, plate girders, or box girders. The design of the girder depends on the size of the bridge and the nature of weight that it will support.
Girder Bridges You May Recognize: If you’ve ever driven over the incredible Coronado Bridge in San Diego, then you’ve been supported by the likes of a girder bridge.
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