Look at the Alaskan Way Viaduct Replacement Program to see the extent that WSDOT goes to for earthquake preparedness. Bertha and the tunnel aren’t the only innovation they’re pursuing. WSDOT is stepping up the standard from “don’t collapse” (which is a fine idea) to “no damage” (a much higher standard.) The new standard is so high that this will be the first in the world demonstration project.
We have to prepare for earthquakes, but as we’ve seen with the damage from the last major quake, concrete crumbles when shaken too hard. The new technology lets the bridge flex instead of break. Their target, a 7.5 quake. Rebar that remembers its shape set in concrete that flexes instead of cracks has the potential to create bridges that are back in operation much sooner after the event. Considering our exposure to earthquakes and the number of bridges and overpasses in the area, such a technology could mean the difference between billions in more damage or a city that recovers far more quickly.
The idea is simple, but making it work at the scale of a bridge is the hard part. The rebar is made from rods of nickel and titanium that retain a memory of their original shape. They can be shaken and twisted and return to normal. The concrete is made bendable by the inclusion of composite fibers. Both the rebar and the concrete are much more expensive, but they don’t need to build the entire bridge from them, just the top part of the columns. In this case, they’re the top five feet of two columns that support the northbound lanes that lead into downtown.
They may cost up to 90 times more than normal construction, but the cost of closing major routes to the city isn’t cheap either, especially when repair costs are included. As with other new technologies, as it is developed the costs should come down.
This is a test. This is only a test, because the technology is new. It’s been tested in the labs of the University of Nevada, Reno. This will be its first real world trial. Even without a quake, there’s a lot of testing to do: construction techniques, durability, maintenance, and repair as needed. The salt air and heavy traffic will be real, not lab approximations. Let’s just hope it doesn’t get any real quake experience, and definitely not a 7.6.