Salt Lake City’s new Public Safety Building utilizes a steel moment frame and viscous dampers to protect against earthquakes, while nonreflective glass and a large public plaza signal the building’s openness to the community. GSBS Architects
The new public services center in Salt Lake City is designed not only to survive a 2,500-year earthquake, but to remain in operation in the event of such a dramatic event, all while using no more net energy than it generates.
July 30, 2013—Salt Lake City is not the first place one might think of as being vulnerable to earthquakes, but two faults run through city, including the 240 mi Wasatch Fault. According to the Utah Geologic Survey, over the last 6,000 years, at least 19 earthquakes severe enough to rupture the ground surface have occurred on the Wasatch Fault.
While the last earthquake in the area occurred in 1600, city leaders are taking no chances. When work began on the new Public Safety Building (PSB) in Salt Lake City, designers and engineers were tasked with creating a building capable of withstanding a 2,500-year earthquake. What’s more, the $125-million building, home to the city’s police and fire departments as well as its emergency call dispatch center and emergency operations center, is engineered to do more than simply not collapse under a major earthquake. It is meant to remain operational, so that first responders can continue to work during a crisis.
This performance standard exceeds the rigorous standards of California’s Office of Statewide Health Planning and Development, or OSHPD, which governs hospital construction in California, the state that is most widely known for its large earthquakes, and is renowned for its research into, and construction of, systems that help structures resist them.
As the designers from GSBS Architects, the Salt Lake City-based firm that designed the building, considered the goal of having the building remain operational after such a strong seismic event, they realized the demands would have “pretty dramatic impacts on the structural system as well as the nonstructural elements of the building,” says Kevin Miller, AIA, a principal of GSBS.
They turned to engineers from Dunn Associates, Inc., of Salt Lake City, to oversee the structural engineering on the project. Dunn’s engineers evaluated a number of lateral systems that could resist the earthquake loads, including a standard concrete-and-steel frame. But the best option turned out to be a steel moment frame backed up by a series of viscous dampers. “What it was able to provide in terms of energy dissipation and its cost—it maximized cost per energy dissipation,” says Christopher Olson, S.E., a principal of Dunn Associates. Not as stiff as concrete, steel moment frames have very ductile joints, Olson says, which allow them to absorb a lot of energy, protecting beams and columns—and the floors they support.
Given the complexity of the work, Dunn brought in another structural engineering firm, San Francisco-based Holmes Culley, as special seismic consultants. Richard Dreyer, S.E., a principal of Holmes Culley, says that the steel moment frame works better in conjunction with the dampers, which permitted a light, more efficient use of steel. The dampers themselves are basically large shock absorbers that help reduce distortion in a seismic event, reducing the amount of acceleration each floor experiences during a seismic event. Those forces, Dreyer adds, are what “throws your equipment around, rips your ceilings apart, knocks your light fixtures out.”
The Public Safety Building bills itself as the largest net-zero
building in the United States, thanks in part to energy modeling
that predicted energy use during the building’s design. GSBS
But securing the building’s structural systems was only part of the challenge. “All the building systems have to be designed to resist the forces that the earthquake will impose on them as they exist in the building,” says Miller. “Design of the structure is actually relatively easy compared to dealing with all of the nonstructural elements that had to come up to snuff.
“Mechanical systems have to run. Electrical panels can’t shake themselves lose and quit functioning. Ceilings can’t fall down and disrupt operations,” he adds. “The partitions have to be designed in a way that they can move with the way that the building will move when it’s subjected to those forces.”
This meant that subcontractors and suppliers on the project had to supply equipment that met the design team’s strict standards. An air-handling unit that was supposed to be placed on the roof, for example, had to meet the predicted force level of an earthquake not only in its internal components but in its connection to the building’s roof. The standards were so tough, in fact, that the system couldn’t meet them, and the unit was relocated to the ground floor.
All of the mechanical and electrical systems were designed in accordance with rigorous specifications and many pieces of equipment were subjected to shake-table tests to mimic actual earthquake conditions. “Some of them work afterward,” Dreyer notes. “Some of them don’t. Some of them fly apart and need to be modified or respecified.”
In addition to making the building more earthquake resistant, engineers also had to meet federal antiterrorism guidelines. To comply, Dunn conducted an analysis of the building to test the PSB’s ability to remain standing if any one of its columns was to be destroyed. The analysis impacted how the beams and columns are connected. In typical beam-to-column construction, Olson notes, a single plate might be welded to the column, and that would be bolted to the beam. The PSB has more robust connections around its perimeter, however. There, the web of beams framing into the columns is sandwiched between two clip angles. Additionally, the building is fitted with blast-resistant—and in some cases bullet-resistant—glass.
And if seismic stability and safety weren’t enough, 315,000 square foot project is also the largest net-zero building in the country. (The building itself occupies 172,000 sq ft; the two-level underground garage adds another 143,000 sq ft.) An older plan for the PSB projected that the building would achieve a silver rating in the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) program, but the design team decided to exceed this. “We approached the initial response to the RFP [by] saying, you can do better than this, and we’re the guys who can help you get there,” Miller says. “It isn’t going to take more money and it isn’t going to detract from your programmatic requirements.”
GSBS had dangled the prospect of a net-zero building when it bid on the project, and when the city agreed, Miller says the firm prioritized net-zero equally with the building’s program, budget, and overall quality. Achieving it in a cost-effective manner meant starting with energy modeling that attempted to predict energy usage before and during the building’s design. As the design evolved, new reports predicting energy consumption were generated every week.
The building uses triple-pane glazing, with a high-performance, low-emissivity coating on two of the six surfaces. “I’m not sure there is better glass on the planet you can buy,” Miller says. The building is heated by radiant floor slabs, and in the dispatch center, which has high cooling demands, chilled beams are used as a supplemental system.
Additionally, GSBS worked to reduce the building’s “plug load,” the amount of energy used by appliances or electronics plugged into the wall, by encouraging police and fire personnel to use energy-efficient laptops in the future rather than desktop computers. The facility has one central break room, so that items like coffeemakers don’t need to be plugged in throughout the building.
In a follow-up email to Civil Engineering online, Miller noted that the plug load in an average building may account for about 25 percent of its energy usage; in the public safety building, he adds “where energy use has been decreased so aggressively, we think that the plug loads are likely to account for as much as 40 percent of the total energy use, perhaps more.”
The savings mean, for one, that the mechanical system uses less energy and can be smaller. And it reduces the amount of photovoltaic units that are required to be installed in order to bring the building down to net zero. Typically a building of this size would require the equivalent of four Salt Lake City blocks worth of such units; this building required only a block and a half. (Some of the photovoltaic panels are located off-site.)
“There’s nothing we did in this building that doesn’t pay back in 10 years. Not a single measure, which I’m astounded by,” says Miller. (Even the high-performance glass pays back in about three years, he adds.) What’s more, he says, the technology is very straightforward. “There’s nothing superexotic here.”
The building’s final imperative was its architectural design. Situated in a developing civic campus, it had to stand up to both the Neogothic brown sandstone of the 1833 City Hall building as well as the swooping icon of the nearby library.
To meet programmatic needs that called for collaboration while maintaining the relatively narrow floor plates that help reduce energy use, GSBS settled on an L-shaped design. The ends are joined by an S- shaped curved, which created ample public space on the first floor of the building. Further, since public access is limited to the first floor, the four-story building tapers as it rises. The north facade is all nonreflective glass, which emphasizes the building’s open character and helps harvest daylight with a minimum amount of solar load. The other three facades, meanwhile, are clad with terra cotta panels that echo the brown sandstone on the city county building.
Miller says his key word for the project was balance—between safety and openness (a public plaza outside will host a portion of the city’s annual arts fest) as well as between function and energy efficiency. “What typically happens is people focus on one or two,” he says. “If you only focus on security you end up with a castle. Just focus on sustainability and not function and you end up with a building that doesn’t work for its occupants.”