Part of the fun of travel is going over bridges to get to where you are going, and then also to appreciate the design of bridges while you are going over them.
One of the tourist attractions in NYC for example, is the Brooklyn Bridge — people admire it, take pictures of it, walk across it, read about its history, take pictures of themselves and their family on the bridge, and view the world around it — the East River in NYC, Brooklyn, and the Manhattan skyline.
There are 4 major types of bridge design used for large bridges over big bodies of water:
- Suspension Bridge Design
- Cable-Stayed Bridge Design
- Steel-Truss Bridge Design
- Steel-Arch Bridge Design
We’ll take a quick look at each in this article.
1. Suspension Bridge Design
The Brooklyn Bridge was designed and built by John A Roebling — the most incredible bridge designer of his day, who perfected his skill while building bridges on the fly for the Union Army allowing General Sherman to march through the south — doing the impossible of moving his army across many waterways and swamps.
The Brooklyn Bridge may not look like a suspension bridge — being that it seems all built out of stone — but if you look at it from afar, you realize it is in fact an amazing example of a suspension bridge design technique — or more specifically, the suspension-cable bridge design.
It is the same technique used to build the incredible Verrazano Bridge in 1963, which connected Brooklyn to Staten Island over the inlet to NY Harbor. The Verrazano features steel pillars.
Another example is of course the Golden Gate Bridge in San Francisco.
2. Cable-Stayed Bridge Design
In the last 15 years, the Cable-Stayed bridge design has superseded the Suspension bridge design in use for long-span bridges.
With a Cable-Stayed Bridge, cables fanning out from one or more towers (or pylons) support the bridge deck. The cables, or stays, form a fan-like pattern or a series of parallel lines. The modern cable-stayed bridges give off a ‘shark fin’ appearance.
The Cable-Stayed design it not new — in fact it was designed in the 1600s, and the Brooklyn Bridge is part Cable-Stayed design, part Suspension-Bridge design. But Cable-Stayed bridges are the rage of the last 15 years.
There are four different types of Cable-Stayed design:
- Mono design: a single cable from its towers. This design is rarely used.
- Harp (or Parallel) design: the cables are nearly parallel so that the height of their attachment to the tower is proportional to the distance from the tower to their mounting on the deck.
- Fan design: the cables all connect to or pass over the top of the towers. This is the most structurally superior design, but sometimes a half-fan design is used so that there aren’t so many cables.
- Star design: the cables are spaced apart on the tower, similar to the harp design, but connect to one point or a number of closely-spaced points on the deck. This design is rarely used.
There are also 7 different arrangements of support pillars for Cable-Stayed bridges: single, double, portal, A-shaped, H-shaped, inverted Y and M-shaped.
The new Goethals Bridge, for example, consists of a pair of cable-stayed bridge spans connecting Staten Island with New Jersey.
Another example is the Kosciuszko Bridge in Queens, NYC.
3. Steel-Truss (Cantilever) Bridge Design
Many major bridges built in the 1920’s and 1930’s were of steel truss cantilever bridge design, supported by concrete piers. These bridges offered what is now considered a narrow, 2-lanes-in-each-direction passage.
Examples include the original Goethals Bridge, the Outerbridge Crossing, and the Pulaski Skyline.
4. Steel-Arch Bridge Design
The Bayonne Bridge connecting Staten Island to New Jersey an example of a Steel-Arch Bridge, sometimes called Through-Arch. When it was completed in 1931, it was the longest steel-arch bridge in the world, a title it held for 45 years.
The roadway of a steel-arch bridge is typically attached to and suspended from the arch via cables, but sometimes the arch can be below the roadway and support it (see Zhijinghe Bridge, below).
The roadway of the Bayonne Bridge was amazingly raised by 64 feet in 2019, to accommodate larger ships to pass under it.
A ship capable of passing through the Panama Canal is called a Panamax ship. With the opening of an expanded Panama Canal in 2015, bigger Post-Panamax ships are sailing the ocean’s waters. These Post-Panamax ships were too big to fit under the old Bayonne Bridge, preventing passage to the ports of the Arthur Kill. So the bridge’s roadway was raised.
To raise the roadway — engineers and construction crews built a new roadway above the existing roadway, then connected it via cables to the existing arc, and removed the old roadway. Here is a time lapse of it:
Other Examples of Steel-Arch Bridges
Other examples of Steel-Arch Bridges are:
- Sydney Harbour Bridge in Australia.
- The Hell Gate Bridge in New York City (upon which the Sydney Harbor Bridge was based).
- The Hernando de Soto Bridge in Memphis, Tennessee.
The Hellgate Bridge in NYC connects Queens to Randalls Island.
If the Bayonne Bridge now looks odd because its roadway is so close to the top of the arch — there are some arches built below the roadway, such as the highest steel-arch bridge in the world — the Zhijinghe Bridge in China.
NYC Has Over 2000 Bridges
NYC, being a city comprised of islands, has over 2000 bridges. Staten Island for example, offers all major forms of bridge design — Steel Truss (current Outerbridge Crossing and the old Goethals Bridge), Steel-Arch (Bayonne Bridge), Suspension (Verrazano Bridge), new Cable-Stayed (new Goethals Bridge).
China Has the Most New Cable-Stayed Bridges
There has been a lot of bridge building going on in China the last 20 years, using the most modern techniques. China now boasts the most cable-stayed bridges in the world, although that may change if Donald Trump gets back in the White House in 2024.
Resources
There are a lot of tremendous resources for bridges and bridge design on the internet of course, but a very good magazine to check out is Pittsburgh Engineer — we referenced their Summer, 2018 issue for this article — an issue we happened to pick up at a Bridge Design Conference in Chantilly, Virginia in 2018.
A list of more current Pittsburgh Engineer issues is here:
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