Twelve building projects win AISC’s top steel design awards.

In April, the American Institute of Steel Construction (AISC) recognized 12 structural steel projects in its 2018 Innovative Design in Engineering and Architecture with Structural Steel (IDEAS2) awards program. Conducted annually, the IDEAS2 award is the highest honor bestowed on building projects by the U.S. structural steel industry and recognizes excellence and innovation in the use of structural steel on building projects across the country.

The 12 IDEAS2 winners were selected from nearly 100 submissions received from architectural, engineering, and construction firms throughout the U.S. Each project was judged on its use of structural steel from both an architectural and structural engineering perspective, with an emphasis on creative solutions to the 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 (AESS); technical or architectural advances in the use of the steel; and the use of innovative design and construction methods.

A panel of design and construction industry professionals identified National and Merit winners in three categories based on total constructed value: projects greater than $75 million; projects $15 million to $75 million; and projects less than $15 million. In addition, the panel awarded a Presidential Award of Excellence in Engineering to two projects for structural engineering accomplishment.

The IDEAS2 program also recognizes the importance of teamwork, coordination, and collaboration in fostering successful construction projects. Awards for each winning project are presented to the project team members involved in the design and construction of the structural framing system, including the architect, structural engineer of record, general contractor, owner, and AISC member fabricator, erector, detailer, and bender-roller. The awards are presented to the team members at ceremonies held at each of the winning projects during the year.

“We celebrate these projects and appreciate the savvy, creative people behind them for showcasing the beauty and usefulness of structural steel,” said Charles J. Carter, Ph.D., S.E., P.E., president of AISC. “Our hearty congratulations to the award-winning teams for a great compilation of excellent solutions!”

Following are the 2018 award-winning projects in each category.

150 North Riverside, Chicago.
Photo: Magnusson Klemencic Associates, Michael Dickter

Projects greater than $75 million

National Award: 150 North Riverside, Chicago — The new 54-story, 1.25 million-square-foot, Class A office, pre-certified LEED Gold tower spans across seven active Amtrak lines, was constructed using cranes balanced on barges, and used lifts of the largest steel sections in the world. The tower features a narrow structure at its base and a compact footprint, which opens up to column-free floors above. Just 85 feet at its widest, the site is hemmed by the river and a 30-foot setback to the east, active Amtrak lines to the west, and Lake and Randolph Streets to the north and south. Above Level 8 (the first full floor positioned more than 100 feet above the plaza), the concrete core-supported tower looks like a typical 46-story steel-framed office building. From Levels 4 to 8, a four-story transfer truss with sloping columns “funnels” the tower out of Amtrak air-rights space on the west and onto the developer’s land in a footprint equal to just 30 percent of the tower’s floor area. Although not similarly restricted, the building’s east side was also designed to slope inward to balance forces and provide open access to the expanding Chicago Riverwalk. All 16 sloping columns along the east and west building faces are 65-ksi W36x925 — the largest and strongest rolled steel shapes in the world. At the furthest north and south column lines, the sloping columns are part of a four-story steel truss. Each truss is supported by two mega-columns, each comprised of two W36x925 sections joined together to create an economical and compact super-column carrying 13,500 tons. Between the north and south column lines, the base of each sloping column bears on the central concrete core. Structural engineer for 150 North Riverside is Magnusson Klemencic Associates, Inc., Seattle.

World Trade Center Transportation Hub
(The Oculus), New York City.
Photo: COWI North America

National Award: World Trade Center Transportation Hub (The Oculus), New York City — The main transit hall in the new multi-billion dollar transit station at the tip of Manhattan Island will serve more than 200,000 travelers each day. The Oculus consists of two parallel arches spanning across a 300-foot-long oval-shaped opening in the transit hall roof slab, and reaches a crown height of more than 100 feet. The arches are supported by columns spaced approximately 7 feet apart — the same distance that the columns of the twin towers were spaced. The spaces between the columns and the gap between the arches are covered in glass, which allows natural light to illuminate the 90,000-square-foot main hall. The “wings” of the dove consist of variable-length rafters that extend from the arches to form a roof-like structure, the largest of which is 197 feet long (equivalent to an 18-story building). The entire structure used a total of 11,500 tons of large steelwork pieces. A sequential erection, rather than shoring, allowed the geometry and load paths to be measured throughout construction. Essential to the segmental erection process was the staged construction computer analysis model created for the project. Erection tolerances for the structural steel were exceedingly tight. In order to allow the glazing to fit properly, the steel in the arch and the columns had to be within 1/2 inch of the theoretical design location. The project team used the model to determine the cambered shape of each individual steel segment, the stresses in the structure, and the position of the geometry control points during each stage of the erection. Design architect and structural engineer is Santiago Calatrava. Managing engineer, engineer of record, managing architect, and architect of record are the Downtown Design Partnership, an STV/AECOM joint venture, in association with Parsons Transportation Group.

Merit Award: 111 Main, Salt Lake City — 111 Main suspends the entire perimeter of a 387-foot-tall, 24-story tower above an adjacent five-story theater. An air rights agreement allows the tower to extend above the theater starting at Level 5. Located in a region of high seismicity, a balanced two-way, 3D steel hat truss system at the penthouse roof level balances load and supports 18 perimeter columns and long-span steel floor framing. Six articulated structural steel bearings (typically located at a building’s base for seismic isolation) support the steel hat truss system and direct the compressive gravity and lateral forces from the hat truss to the tower’s high-strength concrete core walls, and accommodate temperature changes of the exposed hat truss. The hanging perimeter steel columns create open office lease spaces free of interior columns as well as a completely column-free lobby with no perimeter columns meeting the ground level. Measuring 28 feet, 1-1/2 inches deep and weighing 1,870 tons, the structural steel hat truss system extends 40 to 45 feet from the core walls. The building is tuned with longer clear spans for the 20 suspended south-side levels to balance the load of the shorter spans in the 23 suspended north-side levels. The central reinforced concrete core walls provide the tower’s only connection to its complex foundation and resist all gravity loads, as well as wind and seismic vertical and lateral loads. Structural engineers are Skidmore, Owings & Merrill LLP, San Francisco, and Dunn Associates, Inc., Salt Lake City.

Merit Award: U.S. Bank Stadium, Minneapolis — Structural engineer Thornton Tomasetti teamed with Dallas-based architect HKS to make the $825 million, 66,200-seat, Minnesota Sports Facility Authority’s vision of a climate-controlled, amenity-rich, multi-purpose venue a reality. Comprising more than 240,000 square feet, with some panels measuring more than 420 feet in length, the three-layer Texlon ETFE (ethylene-tetra-fluoro-ethylene) polymer film, air-pressure-stabilized pillow system covering the south-sloping roof of U.S. Bank Stadium is the largest transparent ETFE roof in North America. The stadium features five, 55-foot-wide by 75- to 95-foot-high, curtain wall-clad structural steel hydraulic mechanized pivoting wall panels. The lightweight ETFE enabled structural engineers to provide primary roof support with a single, 970-foot steel ridge truss, resulting in cost savings and a striking visual lightness. Orchestration of such a large and complex structure required the use of the software Rhino with the parametric plugin Grasshopper. The design team used Grasshopper to optimize the roof pitch and slope to minimize snow accumulation and reduce roof snow loads. Thornton Tomasetti’s Advanced Project Delivery approach employs specialized connection design engineers and steel detailers working side-by-side with the structural engineering design team to conceptualize the connections early in the design phase once member geometry is set and initial force magnitudes are available. Transfer of connection design information was validated for constructability by Thornton Tomasetti’s modeling the connections in the 3D fabrication software, Tekla Structures. Coordination items were addressed real-time through the use of a shared live Tekla model utilizing a Panzura system that allowed Thornton Tomasetti’s engineers to work side-by-side with the fabricator’s detailer.

U.S. Air Force Academy Center for Character and Leadership Development, Colorado Springs, Colo. Photo: SOM © Magda Biernat

Projects $15 million to $75 million

National Award: U.S. Air Force Academy Center for Character and Leadership Development (CCLD), Colorado Springs, Colo. — The CCLD, serving as an education and research center, features a cantilevering 105-foot Skylight consisting of diagonal steel plates composed in a triangular grid and precisely calibrated to resist lateral forces due to wind loading. This calibration was achieved by considering the deflected shape of the Skylight geometry under an inward pressure. When combined with the original geometry, this deflected shape became the inner boundary of the Skylight’s steel plates, providing a varying depth across each face. The product is a triangulated system of plates of varying depth, which creates a normalized stiffness profile across each face to provide a stable base for attachment of the glazed cladding units forming the outer skin of the Skylight and allows for the optimized glass joint dimension. The AESS is devoid of all embellishment or ornamentation. Through the use of an iterative analysis and design method, structural steel was added only at locations where it was required by the performance of the structure, resulting in maximized material efficiency. Analysis of the Skylight also included consideration of both global and local buckling analyses for geometric and material non-linearity, as well as a check of stresses in the plate members to highlight the flow of loads through the structure and areas of stress concentration. Architect and structural engineer is Skidmore, Owings & Merrill LLP, New York City.

Merit Award: University of California, Davis Jan Shrem and Maria Manetti Shrem Museum of Art, Davis, Calif. — The project’s signature feature is the 50,000-square-foot undulating “Grand Canopy” that covers the building and most of the remaining site. The varying angles and porosity of the canopy infill members filter and reflect sunlight. Structural steel was the best material to meet this architectural challenge. A set of irregularly shaped one- and two-story pavilions — providing gallery, studio, community, administrative, and service space — have concrete fill on metal deck diaphragms supported by steel beams and girders, with steel columns bearing on spread footings and grade beams. Steel framing efficiently supported the long-span roofs over large galleries and could be manipulated to address complicated skewed conditions, sloping and intersecting roofs, and various cantilevered regions. Buckling-restrained braced frames (BRBFs) serve as the lateral force-resisting system in the pavilions. The canopy is supported by round hollow structural sections (HSS) of varying diameters ranging in height from 15 feet to 35 feet, all supporting HSS14x10 girders and beams. They, in turn, support triangular, perforated aluminum infill beams of varying spacing, orientations, and perforations. The canopy columns are each founded on a concrete drilled pier, creating a “flag pole” system of cantilevered columns. The canopy is tied to the building pavilions, so lateral forces are shared by the cantilever columns and the BRBFs, and the canopy girders function as seismic collectors. Structural analysis used RAM Structural System for gravity design of the composite framing of the building and a SAP 2000 model that included both the building and the canopy for dynamic analyses of wind and seismic loading. Structural engineer is Rutherford + Chekene, San Francisco. Consultants include Degenkolb Engineers, San Francisco; Front, Inc., Brooklyn, N.Y.; and WSP | Parsons Brinckerhoff, San Francisco.

Merit Award: Apple Union Square, San Francisco — The addition of a new structure over a functioning below-ground ballroom and loading dock that serve the neighboring hotel required creative solutions for the existing building alterations as well as for the new structure. The new alterations are intricately woven into the existing structural fabric. The project comprises three volumes above ground — the store, the bar building, and the plaza. The unique features of the store — including tall sliding doors, a bridge-scale transfer truss, a grand cantilevered floor, a voluminous interior space, and ductile seismic bracing — were all made possible because of structural steel. A significant portion of the steel frame was constructed of wide-flange shapes, HSS, and built-up sections. The south façade has a pair of tall sliding steel-and-glass doors — some of the largest ever built — each measuring 42 feet tall by 20.5 feet wide. Special concentrically braced steel frames comprise the seismic lateral force resisting system in both directions. The braced spine is built on a substantial steel transfer truss that spans over the below-ground ballroom. The second-floor cantilever is constructed of tapered built-up steel beams, with tuned mass dampers to reduce the vibration response. Lightweight tapered steel trusses support the roof and enclose the generous interior volume. Structural engineers are Foster + Partners, London (also architect) and Simpson Gumpertz & Heger, San Francisco.

Merit Award: Daily’s Place, Jacksonville, Fla. — This 5,500-seat performance venue connects a new, 94,000-square-foot indoor football training facility to EverBank Stadium, home of the Jacksonville Jaguars. Both the performance venue and training facility are covered by a fabric roof that is suspended from an exposed steel roof structure that features exposed articulated steel trusses atop a single-layer membrane hung below. Exposed V-columns around the perimeter serve as vertical load-bearing members while economically resisting hurricane-force winds. Fifty-foot-tall rolling doors make the spaces flexible, enabling the facility to host a wide variety of events. The cost-efficient marriage of exposed structural steel with a specialized, shimmering fabric membrane allows the structure to appear opaque during the day and become translucently alive at night via distinct lighting from within. To meet an accelerated timetable, the integrated project team implemented a fully digital delivery process that eliminated sequential handoffs of documents. A central information database (CID) created from the architect’s Rhino model was crucial to this process. Every participant drew data from the CID, which defined the complex workpoint geometry for the entire project, feeding structural and documentation software platforms including Rhino, Revit, SAP 2000, and Tekla to seamlessly develop the raw architectural form into a fully connected Tekla model that was delivered to the successful steel bidder. Structural engineer and connection designer is Walter P Moore, Kansas City, Mo.

North Transfer Station Rebuild, Tipping, and Transfer Building, Seattle. Photo: Integrated Design Engineers

Projects less than $15 million

National Award: North Transfer Station Rebuild, Seattle — The station’s new $12 million, 67,000-square-foot Tipping and Transfer Building superstructure was designed by a structural engineering partnership between Integrated Design Engineers and CDM Smith. The building is used to collect and sort waste destined for landfill using the flat-floor unloading and sorting method, and is equipped with noise and odor reducers and a mist sprayer that reduces dust. A 150kW solar array and a green roof covers 80 percent of the building’s roof area. The building’s lower-level southwest corner had to be clear of columns and walls to allow truck entrance into the building after driving down the ramp from the street. In addition, the upper-level of the building had to be column-free for its full 200-foot span. A solution called the “floating corner” comprises a 50-foot cantilever truss and a 120-foot main transfer truss system that supports the weight of the entire building at its southwest corner. The main transfer truss at the south face is supported by a double W30 beam embedded in the concrete slab on the east, and a full-story cantilever truss on the west. The full-story truss depth was selected to optimize the structural weight and allow top and bottom chord stabilization. The complexity of these trusses lies in the multiple-stage camber that ensures the trusses are at the correct elevations when the building is completed and loadings applied, as any unpredicted deflection would impact the building’s tri-chorded roof trusses. The upper level of the building had to allow for a 200-foot span of open space without exceeding a roof structure depth of 7 feet (a span-to-depth ratio of L/28).

Merit Award: Riggs CAT Headquarters, Little Rock, Ark. — The new headquarters’ most defining feature is a large western-facing porch. Its cantilevered tapered ends are capped with a standard galvanized steel grate cornice that lightens the edge, filters sunlight, and emulates a shovel blade lifted in the air. The new building’s 163-ton steel structure acts as a large open shed, sheltering key programmatic elements while creating two distinct display (public) and activity (private) lawns. A southern roof overhang and galvanized grate balcony shield direct sunlight but allow indirect light, a key sustainable strategy. Structural engineer is Bernhard TME, Little Rock, Ark.

Promedica Corporate Headquarters, Toledo, Ohio.
Photo: Scott Withers – HKS

Presidential Award of Excellence in Engineering

Promedica Corporate Headquarters, Toledo, Ohio — ProMedica Headquarters is an adaptive reuse of two buildings: the historic Daniel Burnham-designed steam plant constructed in 1896 as well as a Brutalist bank building, both of which are sited adjacent to Promenade Park on the Maumee River at the heart of downtown Toledo. Transformation of the historic steam plant to a 124,000-square-foot office building posed numerous challenges. Inside the steam plant shell, a new four-story office space was created that utilized the existing roof and existing north, south, and west masonry walls to enclose the space.  The footprint of the office building, however, extends outside the original steam plant walls toward the Maumee River on the east. Structural steel was utilized for the architectural desired openness of the headquarters, with most of this steel being exposed. The floor plan inside and outside the steam plant walls consists of large bays (50 feet by 32 feet) to maximize column-free office space. These bays were only possible using wide-flange steel composite beams with up to 2 inches of camber. These beam cambers were closely monitored while pouring the composite floor slabs (3-1/2-inch normal-weight concrete on 3-inch composite deck). Three-inch composite deck was utilized to reduce the quantity of steel pieces, reduce tonnage, and to create the minimalist industrial feel to match the history of the site. Floor-to-floor heights were also limited by the existing steam plant height, thus the majority of the floors utilize beam depths of 24 inches or less. The existing steam plant utilizes pairs of steel lattice columns at roughly 16 feet on center, which support steel roof trusses that span approximately 71 feet, 8 inches between the east and west walls. The lattice columns are set inside the existing masonry walls. Structural engineer is HKS, Inc., Dallas.

Hard Rock Stadium Shade Canopy Erection Plan, Miami Gardens, Fla. Photo: Hillsdale Fabricators

Hard Rock Stadium Shade Canopy Erection Plan, Miami Gardens, Fla. — Erecting a 14-acre structural steel shade canopy weighing more than 17,000 tons over an existing NFL stadium presented unique challenges to the project team. Structural engineers Ruby+Associates, Bingham Farms, Mich., provided full erection engineering services to fabricator/erector Hillsdale Fabricators. The canopy, designed by architect HOK and structural engineer Thornton Tomasetti, Washington, D.C., was part of a $500 million renovation of the 65,000-seat stadium. The canopy is supported by eight supercolumns. Transfer trusses spanning between pairs of supercolumns support a 350-foot-tall spire near each corner of the structure. Sixty-four structural cables, up to 5 inches in diameter and up to 300 feet long, extend from the top of the masts to suspend portions of the canopy. Ruby developed a steel erection plan requiring minimal shoring and no alterations to the existing stadium. A temporary falsework system was shoehorned into each corner of the stadium. The falsework system allowed for installation of the lower mast section and cross transfer truss. After these members were installed, the falsework was removed. To predict the construction stresses and deformations, as well as cable loading/deformation at each stage of erection, a sophisticated analytical model was prepared using SAP 2000. The SAP model accurately predicted the behavior of the extremely indeterminate structure, minimizing the number of costly and cumbersome cable readjustments.

For more information about the IDEAS2 awards and the winning projects, visit

Information provided by the American Institute of Steel Construction (