City Creek Center Retractable Roof Wins National Architecture and Engineering Award
September 4, 2013 from American Institute of Steel Construction
(Chicago, IL) – The retractable roof at City Creek Center in Salt Lake City has earned national recognition in the 2013 Innovative Design in Engineering and Architecture with Structural Steel awards program (IDEAS2). In honor of this achievement, members of the project team were presented with awards from the American Institute of Steel Construction (AISC) during a ceremony held last week at City Creek Center.
Conducted annually by AISC, the IDEAS2 awards recognize outstanding achievement in engineering and architecture on structural steel projects across the country. The IDEAS2 award is the highest, most prestigious honor bestowed on building projects by the structural steel industry in the U.S. and recognizes the importance of teamwork, coordination and collaboration in fostering successful construction projects.
Project team members include:
Master Developer: City Creek Reserve, Inc., Salt Lake City
Retail Center Owner/Operator: Taubman Centers, Inc., Bloomfield Hills, Mich.
Architect: Hobbs + Black Architects, Ann Arbor, Mich.
Structural Engineer: Magnusson Klemencic Associates, Seattle
General Contractor: Jacobsen Construction, Salt Lake City
Steel Fabricator: Ducworks, Inc., Logan, Utah (AISC Member/AISC Certified Fabricator)
Steel Erector and Mechanization Consultant: Uni-Systems, Minneapolis (AISC Member)
The City Creek Center Retractable Roof project is a National award winner in the category of projects $15 Million to $75 Million, making it one of only four projects around the country to receive the National honor. Each year, the IDEAS2 awards honor National and Merit award winners in three categories, based on constructed value: projects less than $15 million; projects $15 million to $75 million; and projects greater than $75 million. Each project is judged on its use of structural steel from both an architectural and structural engineering perspective, with an emphasis on: creative solutions to project’s program requirements; applications of innovative design approaches in areas such as connections, gravity systems, lateral load resisting systems, fire protection and blast; aesthetic and visual impact of the project; innovative use of architecturally exposed structural steel; technical or architectural advances in the use of the steel; and the use of innovative design and construction methods.
Beginning in 2002, City Creek Reserve, on behalf of The Church of Jesus Christ of Latter-day Saints, developed plans to transform two-and-a-half Salt Lake City “mega-blocks” just south of Temple Square with a mixed-use development featuring retail, residential and office space, all utilizing shared underground parking. City Creek was conceived to revitalize and enliven the city’s downtown core. One of the most ambitious urban redevelopment projects in the U.S., construction began in 2006. When it opened in 2012, City Creek Center, the retail centerpiece of the project, was the first regional shopping center to open in the U.S. in six years. The development features a 1,200-ft recreation of historic City Creek that meanders through plazas, walkways and gallerias spanning six acres of green space that provide a park-like setting for shoppers, office workers, residents and visitors. Developers wanted an urban, open-air setting but also needed the assurance that retail businesses would be protected during inclement weather.
After studying many skylight possibilities, structural engineer Magnusson Klemencic (MKA) produced a retractable roof concept that would fully meet developers’ needs. Uni-Systems was selected as the design-build contractor, with MKA as their structural engineering sub-consultant, and Ducworks as the steel fabricator. The resulting retractable, barrel-vaulted roof is configured in two sections, each spanning one city block.
“Having a roof spanning two city blocks that can be transparent and open and close is amazing,” commented Charles C. Porter, principal and cofounder of Development Management Associates, LLC, Chicago, and a judge in the competition.
Each section is 240 ft long and 58 ft wide, with a slight S-shape that echoes the curve of the signature creek below. The precision-sculpted steel and glass transparently shields patrons when closed and disappears from sight when open, connecting nature with the areas below.
For each block, the retractable roof is comprised of three pairs of glass-covered, arching panels that cantilever 33 ft from the adjacent structures over the retail concourse. When closed, all six panels seal together and create an air- and water-tight barrier. To open, the panels part in the middle and retract onto the building structure as the panels lay down out of sight from below.
Key to the laying down action are innovative whalebone-shaped ribs that support the glass roof. Each roof panel is comprised of three parallel whalebones made of curved and tapered welded steel box girders that run from the tip of each panel’s arch to the end of its backspan. The glazed portion of the three whalebone arches are joined by four purlins made of 8-in. A106 Grade B pipe and one purlin of HSS 10 ¾ x ½ in. ASTM A500 Grade B tube.
The purlins are designed with concealed connections that are invisible from below and provide attachment points for 6-ft, 4-in.-sq panes of glass. A typical roof panel is glazed with 72 panes of glass, each weighing approximately 300 lb, although the size of each panel varies because of the roof’s curvature.
The three whalebone backspans are connected with rectangular HSS ASTM A500 Grade B tubing in a K-brace configuration to provide shear stiffness between them. In order to meet special finish and detailing requirements, the side and bottom whalebone girder walls were ground and filled to produce perfectly flat plane surfaces, and a Tnemec Fluoronar paint system gives the whalebones and purlins a high-quality metallic finish.
The whalebones were built at Ducworks’ fabrication facility in two sections using custom- designed fixtures and joined with a plate-welded connection to accommodate the unique geometry. The pre-assembled rail girders and whalebones were hoisted onto the roof, and the panels were assembled in place.
Each 10½ -ton whalebone is supported by a 27-in. double-flanged steel wheel located at the bottom of the arch and two guide rollers located at the end of the backspan. The wheel follows one geometric path on top of the rail girder, and the guide rollers ride an inclined track along the bottom of the rail girder. As the guide rollers travel up the incline, the roof’s cantilevered front edge dips down, causing the roof to lay down, with the wheel as the vertical rotation point. The guide roller track surface is a heat-treated, hardened plate welded to the A572 Grade 50 steel rail girder.
An industrial computer located in a remote control room operates the retractable roof, which travels up to 8 ft per minute and opens or closes in approximately six minutes. Each panel has a unique operating sequence to prevent the panels from interfering with one another as the seals engage and disengage. The roof’s curvature, along with the complex seals and intersecting panels, made the control system the most complicated ever developed by Uni-Systems.
The 13 IDEAS2 winners for 2013 were chosen from nearly 100 submissions received from architectural and engineering firms throughout the U.S. Each submission is reviewed and award winners are selected by a nationally recognized panel of design and construction industry professionals.
The IDEAS2 award dates back more than 70 years to the earliest years of AISC’s existence. Roger E. Ferch, P.E., president of AISC, said, “The entire City Creek Center Retractable Roof project team has shown how structural steel can be used to create structures that combine beauty and practicality. The result is a retractable roof structure that serves its purpose extremely well, while providing an example of what can be achieved when designing and constructing projects with steel.”
High-resolution images of the City Creek Retractable Roof project are available upon request by contacting AISC’s Tasha Weiss at 312.670.5439, [email protected]. To learn more about the IDEAS2 awards and to view all of this year’s winning projects, visit www.aisc.org/ideas2.
Photo Credit: Magnusson Klemencic Associates
For more information contact:
American Institute of Steel Construction
The American Institute of Steel Construction, headquartered in Chicago, is a not-for-profit technical institute and trade association established in 1921 to serve the structural steel design community and construction industry. AISC’s mission is to make structural steel the material of choice by being the leader in structural steel-related technical and market-building activities, including: specification and code development, research, education, technical assistance, quality certification, standardization, and market development. AISC has a long tradition of service to the steel construction industry of providing timely and reliable information.
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