A Non-Moving Experience

Historic Utah State Capitol Restoration Incorporates Unique Seismic Upgrade

Life safety, greater efficiency, restoration of original architecture all major aspects of this once-in-a-lifetime project.

by Sheila Bacon

When planning efforts to renovate the nearly century-old Utah State Capitol building began in 1999, the historic structure’s preservation board sought to fulfill three main goals: preserve life safety, maximize efficiency and restore the building’s original architecture as closely as possible.

Throughout the nine-year effort, the project team not only met these objectives but pushed the envelope in terms of forward-thinking design and construction.

Originally constructed in 1915, the 320,000-sq-ft Capitol closed in 2004 for a $212 million renovation and seismic upgrade. It reopened to the public on Jan. 4.

The Capitol overlooks downtown Salt Lake City and houses the Utah State Legislature; the governor’s and lieutenant governor’s offices; the attorney general; the treasurer; and the auditor, all of whom moved to other buildings during the four-year construction process.

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With the Capitol building located perilously close to the active Wasatch Fault, planners were aware of the looming threat of a sizable earthquake. Their fears were further realized after an early “historic structures” evaluation painted a bleak picture of the aging building’s structural makeup.

“The Capitol was built at a time when there was no earthquake engineering and nothing deliberately incorporated into the structural system to account for earthquake motion,” says Jerod Johnson, principal of Reaveley Engineers + Associates, the project’s Salt Lake City-based structural engineering firm.

Engineers found that the amount of reinforcement in the existing frame was minimal and the brittle concrete would likely cause the structure to start coming down in the event of an earthquake. The investigation found that the quality of the concrete diminished the higher up the building went.

The highest compressive strength about 5,600 psi was found in the basement, but in areas around the dome, the concrete quality was so poor that investigators could brush it away with their fingertips. Instead of the minimum required strength of 2,500 psi, concrete in some of these areas measured below 900 psi.

“Chalk’s strength is 300 psi,” says David Hart, president of the Utah State Capitol Preservation Board (the building’s owner) and the Capitol’s architect.

To protect the structure and its inhabitants against a future quake, the interior was completely gutted, new mechanical and electrical systems installed, the rotunda stabilized and concrete shear walls placed in select locations. The most far-reaching upgrades, however, were placed beneath the Capitol’s foundation.

Below-grade Base Isolation

The project team explored a number of options traditionally used in seismic stabilization efforts. In most large buildings, bracing or load-transfer systems are the most effective and economical.

In the Capitol’s case, where retaining the historic architecture was paramount, x-braces and numerous shear walls would have been intrusive and incongruous with its original design. Rather than addressing the magnitude forces of an earthquake directly, the team decided to use a base-isolation system to decouple the building from its foundation.

Crews would separate the column bases from their footings; install rubber, steel and lead base isolators; then rebuild the footings. If an earthquake hit, the building would essentially “float” on the isolators up to 2 ft from center in any direction. The bulk of the energy up to 80 percent from the earthquake would be transferred back into the ground, greatly reducing the impact to the structure.

The use of base isolators eliminated the need for intrusive x-braces and greatly reduced the number of concrete shear walls required.

To install the base isolators (each cylindrical bearing measured approximately 20 in. high and 36 in. in diameter and weighed 5,000 lbs) beneath 265 of the Capitol’s 380 total columns would require a mammoth effort. The entire 132-million-lb weight of the building would need to be supported not lifted while the footings were removed and the base isolators attached to the ends of the columns.

Reaveley partnered with Forell/Elsesser Engineers of San Francisco on the base-isolation design.

First, a series of micropiles were installed in between the existing columns to provide a point for the location of the temporary jacking system. Four ft above the micropiles, crews placed a two-way system of concrete load-transfer beams each 5 ft wide and 2.5 ft deep around the existing columns. New concrete was cast directly against the existing concrete columns on all four sides.

Temporary jacks were placed between the micropile system and the bottom of the new load-transfer beam above. The jacks were opened up just to the point where the loads would transfer out of the columns and into the load transfer beams, allowing absolutely no vertical lifting of the building.

Once the entire weight of the building was supported, the existing columns’ footings were removed, the base isolators hung in place and new footings constructed below the isolators. Steel locking plates were placed on all four sides of each isolator to prevent them from mobilizing before the entire system was complete.

Once the last isolator was placed and a new concrete mat foundation poured, the locking plates were taken off, the jacks removed and the loads permanently transferred to the new footings.

“We expect that when the ‘big earthquake’ does come, the isolators will perform,” Johnson says.

The use of the load transfer beam in this scenario was unusual, said Johnson, and likely the first time such a system has been used on a structure of this type. The team performed numerous mock-ups before actually using the method to test the load transfer scheme. Most buildings that employ a base isolation system are steel frame buildings, Johnson said, which are more flexible and forgiving. During their early research, the team toured several buildings that had used seismic base isolation system, but the buildings were not made of reinforced concrete. In a steel building scenario, temporary steel beams would typically be welded onto columns to carry the load. Here, the concrete load transfer beams remain a permanent part of the structure. They can be engaged again should an isolator ever need to be examined or replaced.

Extra Support

Support was amplified beneath the four rotunda columns, each of which was supporting a total weight of approximately 10 million lbs. Here, 11 jacks were used to support each column, as opposed to one jack per column elsewhere in the structure. While no vertical movement during the load transfer was allowed in other parts of the building, here contractors were asked to allow for 1/16 of an inch of vertical movement to prove that the load had been captured.

“During the transfers, the exact load had to be taken based on the engineers’ calculations,” says David Marshall, project manager with Jacobsen Hunt Joint Venture of Salt Lake City, the project’s construction manager. “The calculations were fantastic.”

At the opposite tip of the building, considerable work was also being performed. Because the quality of the rotunda dome’s concrete was so poor, the project team had to come up with a method to stabilize it, as well as tie back the terra cotta on its exterior.

Crews applied a 6-in. layer of reinforced shotcrete to the interior surface of the dome with anchors extending from the new shell into the existing shell to engage the exterior cladding. The failing concrete was essentially sandwiched between the new shell on the inside and the existing terra cotta on the outside.

In a Tight Spot

Another challenge unfolded between the walls of the Capitol. Crews had completely gutted the building’s existing electrical and mechanical systems and were working to rebuild them under the watchful eye of the Capitol Restoration Group, which included VCBO Architecture (Salt Lake City), MJSA Architects (Salt Lake City) and Schooley Caldwell Associates (Columbus, Ohio).

The architectural design called for the ceilings to be rebuilt back to their original heights, leaving literally no overhead space to run mechanical ductwork or electrical wiring.

“The architects wouldn’t budge,” says Dave Wesemann, vice president of Salt Lake City-based Spectrum Engineers, the project’s electrical/mechanical/AV designers. “We couldn’t even get 2 in.”

Instead, the mechanical/electrical design team got creative and thickened the walls between offices and other rooms to allow for the mechanical and electrical systems. Instead of placing diffusers in the ceilings, they were incorporated into the walls. Designers had to make sure the walls stacked to ensure continuity of the systems.

“The historical value of the restoration took precedence over many things,” Wesemann adds. “The No. 1 priority was to restore the Capitol to its original look and feel.”

Locating fire alarms and smoke detection systems also required M/E designers to come up with creative solutions. Their originally proposed scheme was deemed too architecturally intrusive by the architects, so designers offered an air-sampling system instead.

Instead of a smoke detector every 30 ft, a piping network that used tiny, 1/8-inch openings to extract air samples was hidden throughout the building. To further disguise the openings, mechanical designers worked with architectural lighting contractor Rambusch of Jersey City, N.J., to located tiny air-sampling tubes within the screw holes of certain lighting fixtures. The samples are then routed to a back-of-house computerized detection mechanism.

Some life-protection systems such as audible fire alarms and strobe lights had to take precedence over the Capitol’s architectural design, but Spectrum minimized the appearance of these as well, particularly in the main rotunda area. Designers performed tests to prove that the reflectivity of the shiny marble surfaces and the acoustics of the rotunda would allow for a scaled-back system that would perform the same as a fully loaded system.

The tests proved that strobe lights effectively bounced off the marble and were visible in all pertinent areas. They also proved that the acoustics amplified the sound of the alarms, so fewer alarm holes had to be installed. Designers then took their case to the fire marshal, who allowed an exception to the code requirements.

Lighting designers were also able to slip in high-efficiency fluorescent lamps in lieu of conventional incandescent lamps in several areas, said Wesemann. The use of dual level switches on many fixtures allows the building’s occupants to dim the lighting when the building is being toured or not in use.

“They can cut the lighting back to historic lighting levels,” said Wesemann. “This not only gives (the spaces) a historic feel, but also saves energy.”

Early Work

To ensure that the restoration project would proceed with as few hiccups as possible, the Utah State Capitol Preservation Board spent nearly two years at its head end defining the project.

“Rather than hiring an architect and saying, ‘We don’t have much of an idea of what we want,’ we defined it and told them exactly what we wanted,” says Hart, the board’s president.

The board designated a set of project guidelines and a set of imperatives. The guidelines outlined the things related to the job that were open to discussion, while the imperatives defined what the project had to include.

The construction manager was brought on board before the design team was assembled an unusual move undertaken to ensure that the joint-venture building team would be a fully interactive partner throughout the entire process, Hart adds.

The CM sat in on the selection of the architects and participated in 17 planning workshops held over six months. Dozens of mock-ups were performed on systems ranging from the base isolators to decorative painting to ensure the right materials and methods were used, and subtrades were brought in as required to contribute additional information.

“We probably did a dozen different mock-ups just on door casings,” says Jacobsen Hunt’s Marshall.

The subcontractor selection process for particular trades was equally unique. Under a design/assist process, the selected RFP respondents were assigned to the contractor but worked with the architect to come up with a design. If they met the budget, they were awarded the project. If not, the subcontractors were paid a fee and the information gathered was used to bid the job.

For example, the process was used to select Rambusch, the architectural lighting contractor. The contract called for the restoration of 400 historic light fixtures and the creation of 1,000 new ones.

The process was successful, Marshall says. “Savings were realized because they helped build the scope,” he adds. “It’s a good process when extra technical assistance is needed.”

Hart agrees

“The subcontractors went from consultants to tradespersons,” he says. “(The process) treated the subs and trades as professionals rather than manufacturers.”

Since the Utah State Capitol building’s grand reopening earlier this year, occupants and visitors have marveled at how the historic structure has been restored to its original elegance. But the design and construction team members would prefer that the most crucial upgrades remain unnoticed.

“It’s a compliment when no one can tell that we ripped out a room and worked in concrete shear walls,” Marshall says. “We hope that people can walk through the building and never even know we were there.”

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