Not only Boulder/Hoover Dam but all concrete structures 100 years old or more will be in need of replacement. That why there is talk of dam and bridge replacement to keep our infrastructure from failing.
Wiki has many facts and is an interesting read in general reference, also touches on the naming controversy...
http://en.wikipedia.org/wiki/Hoover_Dam
If your 100 year mark is accurate, why is the Pantheon still standing? It’s approaching 1,900 years.