From Deseret News archives:
Capitol gets its first earthquake 'cushion'
Building to get 265 shock absorbers for its base
Those words were shouted Monday from underneath the Utah Capitol by Norm Davis as he helped guide workers removing the footing of one of the hundreds of columns holding up the massive building.
The two tons of concrete were taken out to make way for the installation of a base isolator, a sort of shock absorber intended to ease the effect of earthquakes on the 135 million-pound structure.
By the time the $200 million Capitol renovation project is completed in 2008, there should be 265 base isolators in place and another 15 similar devices called sliders. They'll be doing the work of the 380 unreinforced concrete columns that date nearly 100 years.
The first base isolator — a pile of rubber and steel plates surrounding an energy-absorbing lead core — was slowly backed under the building aboard a small tractor Monday and eased into position as project officials and members of the news media watched.
David Hart, executive director of the Capitol Preservation Board that's overseeing the renovation project, smiled as the crew successfully finished the installation. But only for a moment.
It will take about 20 months to put in all of the base isolators, and between now and then the stately, 89-year-old building will be especially vulnerable.
"This is the critical element," Hart said of the installation process. The process is laborious. Only 40 column footings can be removed safely at one time before the base isolators are bolted into place. Then new footings for the base isolators — and a new floor to replace the rubble — can be poured.
The final step of the installation will come after that's been done for the entire building. In just one day, Hart said, all of the base isolators will be, in effect, inflated about an inch, first with water and then with epoxy.
That will help them "give" in the event of an earthquake. Engineers have created animations of what the Capitol would look like in the event of a magnitude 7.3 earthquake — known as the "Big One."
The animations show the building jerking violently as it was originally constructed. Just reinforcing it with more concrete would produce similar results in an earthquake. But the base isolators will allow the building to sway more softly.
Or, as the project's structural engineer, Jerod Johnson, describes it, the Capitol will be "gently floating" in a massive quake with much of the shaking motion confined to the building's base.
