Preserving the look and feeling of an old town trolley station, designers of the new Whole Foods store and parking structure at Trolley Square in Salt Lake City, Utah, envisioned a building exterior that would complement the iconic architecture of the century-old brick trolley barns and support buildings. To achieve this look, the new building was constructed with brick-inlay precast panels from Hanson Structural Precast that were carefully crafted to match the hand-laid bricks used on the original structures.
Trolley Square is a mixed-use, specialty retail project in downtown Salt Lake City. Originally a trolley barn in the early 1900s, Trolley Square is now an upscale marketplace with more than 60 shops, restaurants, and entertainment venues situated in four historic buildings.
The new Whole Foods store occupies 44,000 square feet on the northeast corner of the property, with an additional 16,000 square feet set aside for small, speciality retailers within the same structure. On top of the Whole Foods building is one covered level and one open level of parking.
Whole Foods required a building with an open floor plan measuring 163 feet by 300 feet and a minimum clear height of 22 feet. The original design called for cast-in-place framing. This was converted to precast construction when Hanson Structural Precast was awarded the design and production of the precast components.
“The primary reason for the conversion was the speed of erection,” says Roger Arnell, business developer for Hanson. “We were able to show that we could complete the building substantially faster than with conventional construction. There were some contractual problems that had delayed construction to a point that it made a lot more sense and was more economical to convert to precast concrete. Okland Construction had been awarded the construction. So we approached them to make the conversion.”
Hanson components included in the project are prestressed double tees with spans of 60 feet, precast columns, radius wall panels, and flat wall panels. In all, Hanson precast components include 169 wall panels with thin brick cast into the face of the walls, 228 double tees, 63 columns, and 78 beams. Typical wall panels measure 45 feet tall and 10 feet, 8 inches wide.
Creating a battered brick look
Designers selected a battered thin-brick which could be cast into the outer face of specialized precast wall panels.
“The individual bricks,” explains Hanson sales manager Jim McGuire, “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 stripped 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.”
In all 210,000 pieces of thin brick were incorporated into the panels. Some of the panels were cast as radius walls to form the curvature of the building. After casting, the individual panels were shipped in construction order to the jobsite and stood up on footings.
The back-up mix for the concrete panels was a high strength 6,500 psi concrete and was heavily reinforced to do its job. In some locations, specially designed connectors were used to “stitch” together several wall panels to act as a single shear wall. The forces were very high and the loads were transferred into the footings with welded connections and grouted dowels. The stair and elevator towers were also designed as dual load bearing and shear walls.
Wet joints were cast on-site in such a way that they would not be exposed to the building exterior. Creative detailing allowed the exterior brick finish to remain intact while the wet joint connection was completed behind it.