​Case Study: Salt Lake City’s Suspended Skyscraper | SOM

Located at the heart of Salt Lake City’s financial district, at the corner of South Main and East 100 South Street, 111 Main is a Class A office tower that anchors a larger urban redevelopment project in the area. The construction of the building followed a parallel timeline with an adjacent project designed by another architect, the George S. and Dolores Doré Eccles Theater.

The office building and theater, critical elements in the city’s downtown revitalization, contribute to the development of a walkable urban core and help to create a vibrant community. The office tower is targeting LEED® Gold certification and also supports Salt Lake City’s commitment to increased urban density and long-term sustainability.

The structural engineering of 111 Main reflects an innovative solution to a complex site challenge. To ensure the project would not compromise any of the theater’s functionality, the entire structure is suspended from a steel hat truss on top of the building that allows the Eccles Theater to slide under the tower’s south side.

The lobby is enclosed by 35-foot-tall, ultra-clear, low-iron structural glass. SOM worked with the New York office of engineers Eckersley O’Callaghan to develop a sophisticated glass hinge system to meet this height requirement and mitigate seismic movement. The feature provides the office building with a high level of transparency, visually connecting its lobby interiors with the city outside.

A 35-foot glazed facade system for the expansive lobby of the newest addition to Salt Lake City’s skyline. Designed to withstand windstorms and the seismic pressures of earthquakes.

Eckersley O’Callaghan acted as the Engineer of Record for the design of the custom all-glass lobby facade system. Set back from the perimeter, the slender building core allows for an expansive lobby entrance 40 feet tall. However, this also results in significant building movements in the event of a windstorm or earthquake.

While all floor plates move together uniformly, a key challenge was presented at the interface between the hanging building and the entry-level facade, which is base-supported on the ground.

A study of movements, rotations, supports, and rigidity was conducted to define a system that would cope with the immense imposed building deflections.

A kinetic hinge system was developed to accommodate total building vertical movements of three feet, while precision linear slide bearings were employed to absorb lateral building drifts.

Large cantilever structural steel entry portals were designed integrally with the glazed facade system. Incorporation of architectural timber fins was accomplished with a novel approach to laminate wood veneer into the glass assemblies.

Detailed analysis of global movements, post-failure behaviour, and gasket and sealant flexibility was carried out as part of the delegated design requirements to ensure performance throughout the building’s design life.

111 Main’s translucent glass fin facade reflects changing light conditions as the sun traverses the sky. The structural hat truss, situated behind a graduated translucent glass veil, is also visible in the sunlight and, when backlit, appears like a glowing lantern in the night. The result is a building that adds lightness and luminosity to Salt Lake City’s skyline.

MEETING A TALL ORDER

There’s more than meets the eye at 111 Main, Salt Lake City’s most prominent new office building. Behind the glass facade, a feat of structural engineering allowed the 25-story tower to rise on a surprisingly complex site. As with any building in a seismic zone, SOM designed the 387-foot-tall building to withstand earthquakes. The bigger challenge was to accommodate an important new neighbor: the Eccles Theater, a 2,500-seat performing arts center, planned for the adjacent lot.​

DOUBLE DUTY

Photo © Paul Richer

To meet the requirements for both buildings, SOM designed a portion of the tower to be suspended above the four-story theater. All of this had to be delivered on a demanding schedule: the office tower and the theater below would be built at the same time.

HOISTING THE HIGH-RISE

Photo © Paul Richer

An innovative engineering system called a “hat truss” suspends the tower above the theater. This structural steel framework weighs 1,870 tons. To support the tower’s perimeter columns, the truss extends outward 45 feet from the tower’s core walls. These walls are built of reinforced concrete, making the tower resistant to gravity, wind, and seismic forces.

OPEN SPACES

Photo © Cesar Rubio

SOM used a conventional long-span, composite-steel floor framing construction to connect the core walls to the perimeter steel frame and suspended columns. The design brings big advantages: vast, column-free floor plates, as well as a dramatic lobby that can accommodate spillover crowds from the theater next door.

TEAMWORK

Photo © Cesar Rubio

This innovative engineering solution enabled the project teams for 111 Main and Eccles Theater to work independently toward a shared goal. With parallel construction timeframes, the design and construction of the two buildings continued at a rapid pace.

TOUR DE FORCE

Photo © Cesar Rubio (left) and Paul Richer (right)

111 Main was completed in 2016. As one of the city’s most prominent new buildings, it elevates the quality of architecture in Salt Lake City’s evolving downtown corridor. Together with the performing arts center, it’s already seen as a catalyst to revitalize downtown. “It is clear Salt Lake City has a new icon,” said Mayor Jackie Biskupski at the dedication ceremony for 111 Main, “and this is just the beginning.”

Credits

Architects: SOM
Facade Engineers: Eckersley O’Callaghan
Location:Salt Lake City, Utah
Project Completion: 2016
Project Area: 502,610 ft²
Number of Stories: 25
Building Height: 387 ft

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Article via SOM