Traditional Building Portfolio
Palladio Awards

Project: Utah State Capitol, Salt Lake City, UT

Architect: MJSA Architecture, Salt Lake City, UT; Robert Pett, AIA, president, VCBO Architecture, Salt Lake City, UT; Sean Onyon, AIA, partner; Schooley Caldwell Associates, Columbus, OH; Robert Loversidge, FAIA, president

General Contractor: Jacobsen/Hunt Joint Venture, Salt Lake City, UT

 

 

Awards

Restoration & Renovation

Winner: Capitol Restoration Group: MJSA Architecture;
VCBO Architecture; Schooley Caldwell Associates

Base Principles

By Lynne Lavelle

Though its earthquakes are rarely of the magnitudes that make headlines, the state of Utah is a seismically active area. Since 1850, an estimated 35 “events” have occurred in the region, and while they follow no pattern, geological surveys of Utah suggest that those of magnitude 6.5-7.5 occur, on average, once every 50 to 150 years; magnitude 5-6.5 once every 10 to 50 years; and magnitude 5.0 every four years. History has taught us to fear strong earthquakes, the kinds that periodically reduce cities to rubble in a matter of minutes, and with such brutality that they were once believed to be the wrath of an angry god. However, the damage inflicted on structures by smaller seismic shifts is still considerable, if less dramatic, not least because it impedes their ability to withstand “the big one,” whenever it may next arrive. And as we can no more predict an earthquake than prevent one, it pays to assume the worst.

Such was the thinking behind Capitol Restoration Group’s (CRG) recent seismic upgrade and full exterior and interior restoration of the historic Utah State Capitol (1915) in Salt Lake City (see Traditional Building, April 18, 2008, page 18). CRG – an association of VCBO Architecture and MJSA Architecture, both of Salt Lake City, and Schooley Caldwell Associates of Columbus, OH – was formed in 2002 for the project, with the primary goals of improving life safety and efficiency, and preserving and restoring the building’s historic architectural integrity.

The 320,000-sq.ft. concrete-framed, granite-clad capitol was suffering from years of structural deterioration and modifications that had obscured the original floorplan and left the mechanical and electrical systems behind the times. Seismic investigations revealed the urgent need for upgrades; of chief concern were the rotunda and dome, the top of which was projected to displace at least 20 inches in a 7.2 seismic event. “In doing so it would probably have collapsed,” says Robert Pett, AIA, president of MJSA and lead design architect.

To improve seismic safety, CRG selected a base isolation strategy that had previously been employed at the City Council Building in Salt Lake City (in 1987, it became the very first historic building in the world to undergo the process). Essentially, base isolation detaches the structure from the ground, limiting the transfer of motion. “The capitol is very well-built but very rigid,” says Pett. “We needed to find a means of strengthening the building so that when the earth moves, the building moves at a different frequency. The goal was based on life safety, but there would be damage to the building, repairs would be required after. The purpose was to make sure that there wouldn’t be structural failure, and people would be able to evacuate safely.”

The building foundation was completely replaced and the soil was reinforced with 3,000 individual micropiles before 265 base isolators and 15 Teflon sliders were installed under 280 of the capitol’s 380 concrete columns. Made of steel and rubber with an energy-dissipating lead core, the isolators are cylindrical in shape and range from 34-44 in. in diameter. During an earthquake, they stretch into an oblique shape in any horizontal direction, reducing the impact of seismic forces on the structure above. The selected columns were cut off below new five ft. wide load transfer beams, and the isolators lifted into place while temporary loading jacks provided additional support. As the construction process made the building extra vulnerable, time was of the essence. “The most dangerous time was when some of the building was on isolators and some was not,” says Pett. “These isolators were locked – they couldn’t wiggle. Once everything was in place, they were unlocked in a very short period of time. But, when some of the foundations were removed, and some columns were on base isolation and some were not, there was a disparity of structure that would have made a seismic event very dangerous.”

Above ground, steel straps embedded in the floors absorb horizontal forces, and strategically placed shear interior and exterior walls resist the lateral load. “Except in spaces that were highly historic, the exterior wall actually got thicker,” says Pett. “And around the interior of the rotunda, just below the dome, we added another layer of gunite to strengthen the concrete, which was very, very weak – in some areas it was no stronger than chalk. That too would have crumbled in a seismic event.”

While the base isolation work continued, a host of subcontractors worked on the capitol’s systems upgrades and interior and exterior restoration. Of principal concern was the loss of public space over the years, which in turn had obscured natural daylighting schemes and historic fabric. Among the many modifications to the original floorplan was the division of the original boardroom to make room for a governor’s office and the accommodation of many small committee and hearing rooms, which had closed in the auxiliary corridors, originally designed to open to windows on every floor.

“Government functioned differently when the capitol was originally built,” says Pett. “But as departments grew, they took space from what was originally designed to be exhibit space and grand public space. Those remodels were destructive, not merely in the loss of space, but in that ceilings were removed, lay-in ceilings were added and mechanical and electrical systems were added in a way that interrupted the natural spaces.”

CRG restored the public space to the historic floorplan, removing all non-historic intrusions and allowing natural light to reach the center once again. Drop ceilings were stripped out, modern metal windows were replaced with historically accurate wood windows, and new HVAC and smoke detection systems were run vertically between concrete wall spaces. A physical heating plant was built at a separate location on the site, providing heat and hot water for the building complex, and mechanical equipment was concealed in the attic and the new basement.

“The basement fed the first and second floors, and the attic fed the third and fourth,” says Pett. “We were able to do everything vertically rather than horizontally. In some places we thickened walls, but only where they separated offices. And of course, everything was brought up to accessible and ADA required codes.”

More than 8,000 sq.ft. of historic patterned glazing in laylights above the atria and chambers was replicated, restored and anchored. The unique shingle-system appeared to be failing, and would certainly have been dangerous in a seismic event. “The pieces of glass measured around 2 ft. by 16 in. and were held in a very large steel frame,” says Pett. “The biggest issue for the building officials was that in a seismic event, the glass and frames would start to rack. We took measures to strengthen the frame, but also fastened the glass to the frame with small clips.”

The daylighting scheme was further transformed by the restoration of the rotunda floorlight. Previously, the original cast-glass floor had been removed – possibly for safety reasons – and replaced with green terrazzo. However, the steel frame remained and was structurally augmented for the new multi-layered laminated fritted glass, which filters light all the way down to the first floor.

As work on the capitol was carried out in quadrants, the interior restoration began in each area as soon as significant structural upgrades were completed. Early on, Restoration Associates of Park City, UT, was engaged to analyze and document the original historic paint schemes. Evergreene Architectural Arts of New York City restored the decorative plaster in the senate chamber and decorative paint finishes throughout the building. Archival records proved invaluable in determining historic painting, fabric patterns and lighting schemes; historic lighting fixtures were beautifully restored and replicated by Rambusch Lighting Company of Jersey City, NJ. Finally, modern carpets were manufactured to recreate the originals seen in historic photographs.

Original drawings of the capitol by architect Richard K.A. Kletting showed a large terrace surrounding the building at grade and indicated that the rotunda drum would be constructed of granite. However, both ideas were sacrificed due to soaring construction costs; the terrace was never built and the rotunda was downgraded to terra cotta and finally plaster, painted and detailed to look like stone. CRG’s restoration expressed the original intent, replacing the failing plaster with terra cotta and constructing the terrace. “The terrace was built for two reasons,” says Pett. “One was that when we did the base isolation, it removed the basement’s ability to be occupied and all those spaces had to go somewhere – outside of the building and into the terrace. Secondly, we had the means to finish the original design.”

While the base isolation work ensured the capitol’s future, its restoration was the completion of unfinished business. “Our goal was to avoid removing as much historic fabric as possible and to complete the original plan as conceived by the architect,” says Pett. “It was just a magnificent job on the part of the contractor, Jacobsen/Hunt Joint Venture, to schedule and protect the building and the ongoing work. It required a lot of communication and a lot of people who were dedicated to conserving the building.”  

 

 

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