Recently I posted about varying opinions on the projected longevity of San Francisco’s Golden Gate bridge. Such an iconic bridge will be preserved as long as possible, but repairs and outright remodeling will of course be necessary. In the case of the Golden Gate its earthquake prone location must be considered. Turns out that $455 million is being spent to retrofit several parts of the structure to help it survive the inevitable Big One. The addition of dampeners, steel plating, and even a rebuild of a viaduct are underway or complete. The work will be done in time for the bridge’s 75th anniversary in 2012. Note this critical sentence in the article: “But it will be hard to tell the difference.” Such is the nature of landmark preservation, where the engineering is not only about keeping the bridge up but also causing little visual disruption.