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 become obsessed with-- a tiny bridge on the eastern edge of Golden Gate Park called the Alvord Lake Bridge.
Ernest Ransome, the father of modern rebar, constructed the bridge in 1889. Today, it is a dumpy, cracked and neglected structure. The inside is a surreal tunnel of phony stalactites.
But the Alvord Lake Bridge is, quite literally, the bridge to the modern world. It is one the oldest reinforced concrete structures still standing. The twisted iron bars embedded in the bridge served as the model for the all the rebar containing structures that followed. It is the ancestor to an endless number of reinforced concrete buildings, bridges, tunnels, viaducts, and foundations. Ransome major innovation in rebar was to twist the square bar so that it bonded to the concrete better.
Concrete has incredible compression strength, but it does not have much tensile strength. So if you want concrete to span any significant distance, you need to embed metal reinforcement.
Thanks to CCA Senior Adjunct Professor of Architecture, William Littman (he of the Forgotten Monument) for first telling me about the Alvord Lake Bridge and showing me around. I spoke with Robert Courland, author of Concrete Planet: The Strange and Fascinating Story of the World’s Most Common Man-Made Material (a great book!) and Bob Risser of the Concrete Reinforcing Steel Institute (a great person to talk to!).
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