99% Invisible - 81- Rebar and the Alvord Lake Bridge

Episode Date: June 7, 2013

There’s something about rebar that fascinates me. If nothing else because there are very few things that invoke a fear of being skewered. My preoccupation with metal reinforcement bars dovetails nicely with a structure in San Francisco I’ve kind of … Continue reading →

This is 99% invisible. I'm Roman Mars. There's a well-known literary technique called check-offs gun, named after the Russian playwright. Basically, if a gun appears in the first act, it better be fired in the following act. There are no unnecessary details. You see a gun, that gun gets used to shoot someone. I have a corollary principle of my own invention and it relates to movies where there is a scene at a construction site, and it is this. If on the screen you see an ugly shaft of exposed rebar, somebody is getting impaled. There's something about rebar that fascinates me.

If nothing else because there are very few things that invoke a fear of being skewered. My pathological preoccupation with metal reinforcement bars dovetails nicely with a structure in San Francisco I've kind of become obsessed with a tiny bridge in Golden Gate Park. This is the Alfred Lake Bridge by Ernest Ransom. This is William Littman. He teaches architecture at the California College of the Arts, and he was the first person to

tip me off to the importance of this humble little structure on the very eastern edge of the park. It's sort of the entrance to the park, from the hate side, from the kind of hippie slacker hate area right at the edge of the park, sort of leading into the children's playground. It's not a place that most people really want to linger. It is a spot for drug dealing and various illicit assignations. And that is Robert Corlin, author of Concrete Planet,

giving us a lay of the land. We're in the Albert Lake Bridge, one of the earliest surviving reinforced concrete structures in the world. The bridge was constructed in 1889. It may be the least appealing sort of monument of architecture or civil engineering. On one side, it's cracked where the earth is sort of pressing through. It's covered in mold and lichen. Inside, it's this kind of odd surrealistic tunnel of stalactites that really kind of

look like some sort of folk art, you know, impression of what the surface of Mars might look like. I think it looks like the inside of a giant colon. It's really unappealing to pass through it. It's not well kept up at all. Well, there's nothing remarkable about it. It is an arch. It's actually as much a pedestrian tunnel as a bridge. A pioneering structure in the shape of a dumpy and the collected little bridge. But that's really sad because it is one of the pioneering buildings in the story of reinforced concrete.

Thank you. Thank you. Thank you. Thank you. There are plenty of candidates for the most overlooked, most invisible part of the built world, but reinforce concrete has a good claim to being the most invisible of all. Because if it's made right, you never see the steel skeleton underneath all of a concrete structures that you work in, drive over, walk under.

Reinforce concrete is concrete that is strengthened by the addition of initially iron and then later steel to give it tensile strength. The thing about concrete is it's great in compression, meaning it's with stands a lot of pressure in terms of weight, but it's not very good intention, meaning when you, sort of, spanning long distances it sort of can collapse.

So if you see concrete going high in the air or spanning a long distance, there is metal inside that. And you have this unassuming vanguard of a bridge and its engineer Ernest Ransom to thank for that. Ernst Ransom's principal claim to fame is that he's the father of modern reinforced concrete. The experiments done with reinforcing concrete with iron, previous to Ernst Ransom, were just one off experiments,

a cottage in England, house in New York, and a robot in France. Ernst Ransom experimented with different forms of iron reinforcement until he hit upon what we now call rebar, which is short for reinforcement bar. And his technology was far beyond any of the others who were experimenting with reinforced concrete at the time. A lot of people in Europe and America are playing with putting in bars or

metal into concrete at this time. There's many different techniques and everyone's experimenting. What ransom's sort of major innovation is is he takes sort of square bar that runs through it and he twists it slightly and that gives it an adhesive quality to the concrete itself and sort of stays together much better. Ransom said to come to this idea he found a twisted rubber band in his pocket one day and thought well that's what I'm going to do to this iron bar. I'm going to twist it so it just binds to the concrete better.

You can see a diagram of this twisted rebar in Ransom's 1884 patent. By the way, if you're anything like me, Google Patent Search is the best way to spend time in front of the computer. I can lose hours jumping from patent to patent. Anyway, this innovation of messing with the bar to help it bond with the surrounding concrete is still used to this day. We put defamation on the reinforcing bar so that the concrete will hold on to it. That scoring is probably why I find rebar so ugly and unsettling.

That's Bob Risser right there. I'm Bob Risser. I'm President and CEO of the concrete reinforcing steel institute. I call this C-R-S-I to get the full scope of what reinforced concrete means to the built world. Well, without exaggerating the point, I would say that the significance of reinforced concrete is that modern society is not possible without it. Well as humble as the Albert Lake Bridge is, it is a direct precursor to the Ingalls Sky Scraper built just 15 years later in Cincinnati, Ohio, the

world's first reinforced skyscraper. It also led to bridges, dams, freeways, streets of reinforced concrete. I mean, without reinforced concrete, you would only be able to build a series of unconnected asphalt roads. It's a very humble beginning, but it was from here in San Francisco that the reinforced concrete revolution took over the world. That's why we talk about it being the foundation of civilization. It's also a foundation of modern architecture. It made possible forms that were never possible before, like Frank Lloyd Wright's Guggenheim

Museum, and more recently, Genie Gang's Aqua Tower in Chicago. It's designed to mimic flowing water on the 80s on floors. There are no two floors that are the same. There's no two balcon floors that are the same. There's no two balconies that are the same. But the problem with reinforced concrete, especially if the rebar isn't covered with enough concrete and it's exposed to water and salt, is that the steel inside can rust. And as it rusts, it expands. They expand to almost fourfold its original diameter, destroying the concrete around it while the steel itself is being destroyed by the rust and corrosion.

And when that happens, which it will eventually, reinforce concrete doesn't last the 1000 years that Ernest Ransom and the early reinforce concrete proponents thought that it would. For many many years, the design life was about 50 years. The entire interstate system was built under the assumption of a 50-year design. These days, our organization and others are working with the federal government and state agencies to try to look at 75 and even 100-year designs. Modern reinforced concrete frames encased inside of a building superstructure with normal maintenance will last a lot, lot longer. So don't worry, the Burk-Elifa, the tallest hour in the world, and the tallest reinforced concrete structure is not coming down anytime soon.

But the clock is ticking for most of the reinforced concrete infrastructure that was put up in the middle of the 20th century in the US. People have to realize that all this that they see around them will eventually have to be with a few exceptions, will have to be torn down and replaced because we built with steel reinforced concrete. And the cost of that, it will be trillions of dollars, a unbelievable amount of money. Seriously, the stuff that wasn't properly maintained is coming down. And as you can imagine, a lot of our infrastructure was not properly maintained.

Particularly with public agencies where very frankly, the method has been, and in some cases still is, you know, a reactionary policy rather than a well thought out maintenance routine. Even though Concrete has the illusion of permanence, it is not that way at all. You just build it and forget it. You have to account for going back and taking care of it like you would. Anything else? Ernest ran some left San Francisco soon after he completed the Alvar Lake Bridge. In his book, Re-Enforce Concrete Buildings published in 1912, which is not the most central lighting of text, but in it you can detect a tinge of bitterness in Ransom's words as he describes how his twisted rebar was, quote, laughed down by the technical society in California. He left for the east, thinking that his revolution

of reinforced concrete would have a better chance out there. He left thinking that no one here would fully appreciate his Albert Lake Bridge, that no one here would appreciate this literal bridge to the modern world. And looking at it today, I'm sad to say, that he was right. 99% invisible is Sam Greenspan and me Roman Mars. We are a project of 91.7 local public radio KALW in San Francisco and the American Institute of Architects in San Francisco. You can find the show and like the show on Facebook. I tweet at Roman Mars, but this week, oh my goodness, we have amazing photographs of the Alpha Lake Bridge as photographed by Eddie Joaquim, he just makes the ugliness and creepiness of that place look beautiful and stunning.

You have to check them out. They're at 99%invisible.org. Video Topeon. From PRX.