This tiny bridge is in fact one of the most significant historic bridges in the entire country. It is the oldest surviving concrete bridge with metal reinforcing bars within. The technique of reinforcing concrete with rods or bars, often called rebar, is a practice that quickly took off in the early 20th Century and it remains a common method of producing structural concrete for bridges and buildings even today. As such, this bridge marks the beginning of an important construction technique that has since been in use for over a century. Ernest L. Ransome became an early pioneer in the process when he patented his process of reinforcing concrete with twisted metal bars. These so-called Ransome bars were used in many bridges and buildings and likely was inspiration for other designs of reinforcing rods and bars.
As such, the Alvord Lake Bridge is significant not only as the oldest reinforced concrete bridge in the country but also for its association with a pioneer in reinforced concrete design.
The Alvord Lake Bridge also displays other interesting details. The bridge is built of concrete, but the concrete was formed to have the appearance of stone. Ransome did a very good job of making his concrete look like stone, in fact his concrete simulates the appearance of stone far better than modern stone-shaped formliners used in modern concrete construction today. This is likely because the mix of cement and aggregate in the concrete that Ransome used would have had produced a more rough, stone-like appearance than modern concrete does. Regardless, Ransome's use of concrete formliners to make the concrete look like stone is another technique that Ransome pioneered (and patented) and his technique of using stone-shaped formliners remains in use in concrete design today.
Another unusual detail of the Alvord Lake Bridge is underneath the bridge are decorative concrete stalactites designed to make the underside of the bridge look like a cave. As odd as this detail is, this is an original detail to the bridge. It is possible that this detail was not only an effort to make the bridge look intriguing and perhaps natural in appearance, but it might also have been an effort of Ransome to show the different things that could be done with concrete. The irony of these stalactites is that one of the things that concrete does over the decades if moisture gets inside the concrete is that efflorescence can form on the underside of historic concrete bridges and form white "stalactites" of a sort. In this sense, normally "stalactites" are something you do not want to see on a historic bridge, but in this case, the stalactites are intentional and not related to bridge deterioration.
While Ransome bars may be found in a number of old concrete bridges, the Alvord Lake Bridge is one of only two known surviving bridges that Ernest Ransome himself was involved with building. The other bridge is a private structure on Long Island, New York.
In the years after designing this bridge, Ernest Ransome appears to have eventually also become well-known for his company that produced concrete mixers and other equipment for concrete construction.
This bridge is a designation National Historic Civil Engineering Landmark. It is also a contributing resource to the Golden Gate Park Historic District.
Ernest Leslie Ransome Obituaries With Biographical Information
One of the great pioneers of reinforced concrete construction has passed away. Ernest L. Ransome was an inventor to whom Americans owe a greater debt than could ever be repaid. Only a few weeks before his death
we commented editorially upon his remarkably useful inventions, and in a gracious letter he acknowledged appreciation of our comment.
Source: Engineering and Contracting, Volume 47, 1917
Ernest L. Ransome, a pioneer of reinforced concrete construction, is dead. Mr. Ransome was well known as an inventor of concrete machinery, the Ransome mixer being familiar to builders all over the United States.
The editor of Engineering and Contracting pays Mr. Ransome the following tribute:
Architect and Engineer, Volumes 48-51, 1917
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