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Utah Capitol Rehab Enters ’Most Dangerous’ Phase

Tue May 31, 2005 - West Edition
CEG



SALT LAKE CITY (AP) Crews installed the first earthquake buffer between the state Capitol’s foundation and ground underneath, marking the beginning of the most critical phase of construction and the building’s most vulnerable period.

The $200-million renovation project is designed to protect the Capitol –– and a heavily populated area of Salt Lake around it –– from a 1,300-year magnitude 7 earthquake, which scientists said could happen at any time. Without the project, such a quake would send the brittle concrete building and its enormous dome tumbling.

On May 16, news reporters watched workers install the first of 265 “base isolators,” cylindrical layers of rubber and steel that would allow the building to sway back and forth in an earthquake.

“That gives it stiffness to move as a mass,” said Jerod Johnson, renovation project engineer.

The entire process of installing those pieces will take until October 2006, as crews drag away –– 40 at a time –– integral building structures once engineered to hold everything up. The Capitol has more than 300 of those weight-bearing columns.

In the meantime, they’re crafting intermediary structures to support its enormous weight. As it stands today, ground around the Capitol is dug away and the building sits on stilts aapproximately 5 ft. (1.5 m) high. Hard-hat wearing workers seem to think nothing of crouching a bit and walking underneath the 67,500-ton (60,750 t) structure as they continue to clip and drag out pillars to shift the building’s weight.

The 90-year-old Capitol was built of marble and concrete with almost no reinforcing steel, which analysts said will doom the building without an up-to-date suspension system.

Though other buildings have been similarly retrofitted, project officials said this one brings particular challenges.

To stabilize the Capitol even before they could put in the isolators, workers had to pour a roughly 4-ft. (1.2 m) thick slab of concrete underneath it. But traditional concrete wouldn’t work, so engineers had to use a special formula that would make the new concrete literally stick to the old stuff, said Dave Marshall, general superintendent of the joint venture between architectural firms Jacobsen and Hunt handling the project.

Additionally, existing equipment was too tall to squeeze into the space under the building, so engineers had to modify a mining track vehicle by lowering the driver’s seat and equipping it with a rear lift that can carry the 2.5-ton (2.3 t) stabilizers.

Although strong Utah earthquakes are infrequent, separated by hundreds of years, the record shows them to be fairly regular and particularly violent. In an instant they can raise the Wasatch mountains 10 ft. (3 m) and drop the valley by five, ripping open the land like a zipper. Such a quake would cause widespread damage to older buildings and homes made of unreinforced brick, and snap water and gas lines.

Geologists can’t say with certainty when the next quake will strike, but they theorize a large one could occur any time –– a century from now or tomorrow.

In the meantime, crews are working as quickly as they can to get the project done by its scheduled November 2007 completion date.

“In my mind, as I look at it, every day that passes is a day that brings us closer to an earthquake,” Marshall said.