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Alvord Lake Bridge

Kezar Drive Bridge

Alvord Lake Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: April 7, 2013


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Key Facts

Facility Carried / Feature Intersected
Kezar Drive Over Pedestrian Walkway
Location
San Francisco: San Francisco County, California: United States
Construction Date and Builder / Engineer
1889 By Builder/Contractor: Unknown and Engineer/Design: Ernest L. Ransome of New York, New York

Technical Facts

Rehabilitation Date
Not Available or Not Applicable
Main Span Length
29 Feet (8.84 Meters)
Structure Length
Not Available
Roadway Width
64 Feet (19.51 Meters)
Spans
1 Main Span(s)
NBI Number
Not Applicable

Historic Significance Rating (HSR)

Bridge Documentation

View Historic American Engineering Record (HAER) Documentation For This Bridge

HAER Data Pages, PDF

View Some Noteworthy Ernest Ransome Patents

View A Historical Guide To The California Midwinter Exposition

View The Golden Gate Park National Register of Historic Places Nomination Form

View The Ransome Book: How To Make and Use Concrete

View Ransome's Book, Reinforced Concrete Buildings

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.

The Alvord Lake Bridge was constructed in association with the development of the area that is today Golden Gate Park to enable it to host the California Midwinter Exposition.

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.

The editor had the good fortune to know Mr. Ransome personally, and from his own lips to hear much of the history of his early experiments. Thus, when an architect in San Francisco wished to find a cheaper sidewalk "roof" for a basement than one made of steel I-beams and brick arches, Mr. Ransome's advice was asked. Within a few hours Mr. Ransome had solved the problem, and in a characteristically novel fashion. For brick arches he substituted a concrete slab, and for steel I-beams he substituted steel rods bedded in the concrete. But, as he said, he feared that under the tension of a load the rod3 would slip in the concrete; so his first idea was to thread the ends of the rods and put nuts on the ends. Then it flashed upon him that he could make the entire rod into a "threaded rod" and the entire concrete into a huge "nut" threaded thereon. Forthwith he took a rod of rectangular section and twisted it in a lathe, making what afterward became famous as the "Ransome twisted bar reinforcement."

The first reinforced concrete slab was made, and a new era of building construction was initiated. Nor was Mr. Ransome slow in perceiving the economic possibilities that now presented themselves. He began to design and erect reinforced concrete bridges and buildings, improving steadily in his designs of details, and coincidentally in his methods of manufacturing and placing concrete. His "non-tilting batch mixer"-a device of extreme simplicity-was first designed for his own contract work, and later put upon the market. His tower and hoisting bucket for building work was a still later step, and then came his system of chuting concrete from the tower into the forms.

Mr. Ransome's mind was always active upon some improvement or some new device, yet, unlike many inventors, he did not cease his labors on an invention before it was fully developed. He was exceedingly practical and painstaking. But the necessity of carrying on his business often left him with but few hours to devote to inventive work.

It had often seemed to the writer that society loses enormous benefits every year because men of genius are forced to "earn their daily bread."

If we pause but a moment to consider the rarity of highly inventive talent, we are struck with the great economic loss that occurs whenever an inventor is held, even for an hour, from the exercise of his genius. Was it Edward Bellamy who, in his "Looking Backward," pictured an ideal social state wherein each man was given to do the thing that he could do supremely well? Perhaps such a Utopia is coming sooner than Bellamy dreamed, although not as he dreamed it, and, when it comes, our Ransomes will be free to add not merely one or a score or a hundred labor-saving things to the world's stock, but five or ten times the number.

Mr. Ransome was a man who took the kindliest and most gracious interest in those about him. No person could see him often without feeling both a profound respect for his ability and a great liking for his character. He was modesty personified as. to his achievements, and told how each invention had "evolved" in such a simple, matter-of-fact way that it seemed as if almost anyone might have "evolved" it. But, as some one remarked, the ease with which a powerful and skilled intellect works is the most deceptive ease in the world, as speedily becomes apparent when a weak and untrained mind attacks the same sort of a problem.

Mr. Ransome's father, Frederick Ransome, had also been an inventor, and had patented an artificial stone in 1844. The early training under his father, coupled with his inherited originality, made Mr. Ransome eager to follow a career as an inventor. Now that career has ended, rich in achievement and fascinating as a romance. The history of Ernest L. Ransome's life would form a chapter that would match well with those that Samuel Smiles, in his "Self Help," wrote nearly a century ago about the great inventors of his day.

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:

Mr. Ransome's mind was always active upon some improvement or some new device, yet, unlike many inventors, he did not cease his labors on an invention before it was fully developed, lie was exceedingly practical and painstaking. But the necessity of carrying on his business often left him with but few hours to devote to inventive work.

Mr. Ransome was a man who took the kindliest and most gracious interest in those about him. No person could see him often without feeling both a profound respect for his ability and a great liking for his character. He was modesty personified as to his achievements, and told how each invention had "evolved" in such a simple, matter-of-fact way that it seemed as if almost anyone might have "evolved" it. But, as some one remarked, the ease with which a powerful and skilled intellect works is the most deceptive ease in the world, as speedily becomes apparent when a weak and untrained mind attacks the same sort of a problem.

Mr. Ransome's father, Frederick Ransome, had also been an inventor, and had patented an artificial stone in 1844. The early training under his father, coupled with his inherited originality, made Mr. Ransome eager to follow a career as an inventor.

It is related of Mr. Ransome that many years ago, when an architect in San Francisco wished to find a cheaper sidewalk ''roof" for a basement than one made of steel I-beams and brick arches, Mr. Ransome's advice was asked. Within a few hours Mr. Ransome had solved the problem, and in a characteristically novel fashion. For brick arches he substituted a concrete slab, and for steel I-beams he substituted steel rods bedded in the concrete. But, as he said, he feared that under the tension of a load the rods would slip in the concrete: so his first idea was to thread the ends of the rods and put nuts on the ends. Then it flashed upon him that he could make the entire rod into a "threaded rod" and the entire concrete into a huge "nut" threaded thereon. Forthwith he took a rod of rectangular section and twisted it in a lathe, making what afterward became famous as the "Ransome twisted bar reinforcement.''

The first reinforced concrete slab was made, and a new era of building construction was initiated. Nor was Mr. Ransome slow in perceiving the economic possibilities that now presented themselves. He began to design and erect reinforced concrete bridges and buildings, improving steadily in his designs of details, and coincidentally in his methods of manufacturing and placing concrete. His "non-tilting batch mixer"-a device of extreme simplicity-was first designed for his own contract work, and later put upon the market. His tower and hoisting bucket for building work was a still later step, and then came his system of chuting concrete from the tower into the forms.

Architect and Engineer, Volumes 48-51, 1917

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