Matching the Look of Century-Old Trolley Barns in Salt Lake City, Utah
by Roy Diez, executive vice president, James O. Ahtes, Inc.
From Architectural West May/Jun ’13
Creating an up-to-date design that fits effortlessly within an existing historical context is one of the arts that constitute quality architecture. For the new Whole Foods store at Trolley Square in Salt Lake City, Utah, designers faced the challenge of complementing the iconic architecture of century-old brick trolley barns. Their answer was to utilize brick-inlay precast concrete panels that were carefully crafted to match the hand-laid bricks used on the original structures.
“We were operating in the context of an historical environment and the design was subject to an historical review board,” says Gary Larson, AIA, senior principal at MulvannyG2 Architecture, Portland, Oregon. “Our design concept was to extend that texture, the look and feel of the older buildings, yet keep it sufficiently modern. We were not just mimicking what was there, but were using it as an inspiration for a more modern building. The historic committee was very pleased with what we did.”
A Multiphase Renovation
Trolley Square is a mixed-use, specialty retail project in downtown Salt Lake City. The 14-acre complex was originally built in the early 1900s as trolley barns. In 1945, after the trolleys were shut down, the barns were painted yellow and used to store city buses. Scheduled for demolition in 1969, the property was acquired by a developer. The yellow paint was removed from the old brick and, in 1971, the old barns were converted into a festival-style shopping mall modeled after Ghirardelli Square in San Francisco, Calif. In 1986, new owners added an atrium and food court. In the late 1990s, a Pottery Barn and Hard Rock Café opened and the property was listed on the National Register of Historic Places.
In 2008, a multiphase reconstruction was begun by new owners, ScanlanKemperBard Companies, Portland, Oregon, and Okland Construction, Salt Lake City. This included removal of an existing parking structure on the west side and replacement with a two-level, below-grade garage topped by retail space. The renovation added 35 retail stores and increased leasable space from 225,000 to 350,000 sq.ft. The finished complex is now a themed, upscale marketplace with more than 60 shops, restaurants, and entertainment venues situated in four historic buildings. But the most intriguing aspect of the mall make over was the addition of the new Whole Foods store.
Parking on the roof
The new Whole Foods store occupies 44,000 sq.ft. on the northeast corner of the property, with an additional 16,000 sq.ft. set aside for small, specialty retailers within the same structure. On top of the Whole Foods building is one covered level and one open level of parking, providing 200 stalls. Rooftop, rather than underground parking, was chosen because of the site’s high water table.
The building employs load-bearing precast wall panels with thin brick cast into the face of the walls, precast columns and beams, and prestressed double tees produced by Hanson Structural Precast, Salt Lake City. Some of the panels were cast as radius walls to form the curvature of the building. Typical panels measure 45’ tall and 10’ 8” wide. Whole Foods required a building with an open floor plan measuring 163’ by 300’ and a minimum clear height of 22’. The precast double tees have spans of 60’. Column spacing is 30’ in one direction and 60’ in the other. The building sits on a mat foundation system. Interior walls consist of studs, cavity wall insulation, and sheetrock.
“In the Salt Lake City region, they do a lot of precast buildings and parking structures,” says Larson. “It made sense to use a system that was clearly understood by contractors in the region. The system also allowed us to achieve the brick look we wanted. A large amount of credit goes to how well [the wall panels] were done by the precaster.”
The precast concrete construction provides lateral support and meets the seismic requirement for the region, according to Jim McGuire, sales manager for Hanson Structural Precast. Interior shear walls run through the periphery of the floor plan in such a way that they don’t affect store operations. The stair and elevator towers are also designed as dual load bearing and shear walls. Loads are transferred into the footings with welded connections and grouted dowels.
Shopper access to the rooftop garage levels is by stairs, elevators, and escalators. Automobile access to the garage is via speed ramps. A membrane and secondary slab over the garage floor double tees ensures against water leaks into the store. Storm water is collected internally and routed to detention chambers installed underneath another new, nearby building.
Creating a Battered Brick Look
To fit the building in its historic context, designers selected a battered thin-brick which could be cast into the outer face of specialized precast wall panels. “The precast, thin-brick system was suggested by the contractor,” says Larson. “What we saw when we were shown samples by the precaster is that we could actually achieve what was wanted, a result that looks for all the world like a laid-up brick wall.”
Explains McGuire, “The individual bricks were laid out on the formwork in a special plastic grid that held them in place at the proper spacing while the plastic between each thin-brick formed a concave grout joint when the panels were poured. Once cast, the panels were striped out of the forms and the plastic sheet was removed. The bricks, which had been coated with a thin layer of wax for protection, were then hot-water washed revealing the beautiful character of the brick facing and exposed concrete work.” Alternating scalloped arches were integrally cast into the precast with the brick. “This,” says McGuire, “put the Trolley Square signature on the architecture.”
Precast Cuts Construction Time
“The project went up quickly, thanks largely to the use of precast construction,” says Larson. “When we started construction, the precast panels were well prepared. They were stockpiled and we just kept going.” All the precast structural elements were manufactured off-site under controlled conditions at Hanson’s Salt Lake City plant. This left the jobsite unencumbered until footings were poured. Combining load-bearing elements and masonry cladding in one component proved economically effective.
Precast concrete also helped the team meet sustainability requirements. The durability, strength, and inherent weather resistance of precast concrete represents a tremendous advantage over alternative construction methods. The material stands up well in the harsh environment conditions of Salt Lake City. Other sustainable features of the project include an on-site, storm-water management system, native plants that require less irrigation, additional scooter and bike parking, an extensive plan to divert construction waste from the landfill, and use of regionally produced materials with recycled content, including the precast components. Also employed are low-emission boilers, water-efficient fixtures, high-performance glazing, use of day-lighting, dark sky compliant design, and energy, humidity, and CO2 sensors. All power is obtained from wind energy sources. The store was designated a Three Globe Project by the Green Globes rating system and it is the first supermarket in Utah to receive a Green Chill award for its refrigeration system.
Larson notes several additional advantages to the use of precast concrete construction. “One,” he says, “certainly was price, because it was competitive over conventional concrete. And steel is not a system you want to use in the Salt Lake area because of the use of corrosive salt as a de-icer in winter. Another advantage was the speed of erection. This was important because the store was in a hurry to open. Finally, the precast panels with thin-brick were totally satisfactory aesthetically. That was the capper in terms of their use.”
According to McGuire, precast concrete construction reduced construction time of the main structure by six months and resulted in a cost savings of 15%.