Innovative designs in steel

Ten structural steel building projects chosen from nearly 100 submissions earned national recognition in the 2016 Innovative Design in Engineering and Architecture with Structural Steel (IDEAS2) awards program. Conducted annually by the American Institute of Steel Construction (AISC) for more than half a century, the award is the highest honor bestowed on building projects by the structural steel industry in the United States.

“The 2016 IDEAS2 winners demonstrate that innovation and creativity can be found on building projects of every size and description,” said Roger E. Ferch, P.E., president of AISC. “Steel continues to provide excellent solutions for the entire design and construction team, from architects, engineers, and developers to general contractors, fabricators, and erectors. Congratulations to the award-winning teams for projects that combine creativity, economy, and technical achievement through the use of structural steel.”

A panel of design and construction industry professionals identified National and Merit winners in three categories, based on total constructed value: projects less than $15 million; projects $15 million to $75 million; and projects greater than $75 million. In addition, the panel awarded a Presidential Award of Excellence in Engineering to one project for structural engineering accomplishment, and also recognized one project in a new category for steel sculptures/art installations.

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 steel; and use of innovative design and construction methods.

Presidential Award of Excellence in Engineering
Emerson College Los Angeles, the West Coast home of Boston-based Emerson College, received the Presidential Award of Excellence in Engineering. Located in Hollywood, this $85 million building (structural engineer: John A. Martin & Associates, Inc., Los Angeles) is a small-scale university campus containing below-grade parking, classrooms, performance space, offices, and student housing. The complicated forms and interconnecting spaces required creative structural problem solving to maintain efficiency of material and constructability while upholding the architect’s vision.

The nearly square footprint of the building is based three stories below grade and rises in that shape up to the third level. Above that level, the square shape of the building is broken into two separate pieces: the east tower — a slender rectangular floor plate housing residential units — and the west tower — a combination of academic space and administrative offices in an irregularly shaped slab adjoined with residential units. The two towers continue to climb, with the west tower’s shape continually changing, until the sixth level when the west tower reduces to a near mirror image of the east tower. The towers terminate at the eleventh level roof where they are connected by a helistop spanning over the academic structure below.

Mild reinforced concrete slabs are the gravity framing system for the parking, administrative, and office spaces. The residential towers are framed using post-tensioned concrete slabs, and the academic form is supported by steel beams, steel columns, and concrete over metal deck. Interconnectivity of the multiple systems was addressed by careful detailing and consideration of the construction sequence.

The amorphous shape of the academic building presented further structural challenges because of the two intertwining forms and varying floor-to-floor heights between residential and academic program areas. The academic building features a hanging boardroom, simultaneously reinforcing the architect’s desired massing and providing a column-free entry pavilion at the second level. To support the academic forms, multiple cantilever elements were outfitted with steel cantilever trusses, one supported by the concrete elevator core walls and the other supported off of steel columns terminating at concrete transfer girders. Discontinuous special concentric braced frames and discontinuous steel moment frames were used to transfer lateral forces from the roof of the academic building down to the supporting concrete transfer diaphragm at Level 3.

The primary lateral resisting system below the third level is special reinforced concrete shearwalls. The residential towers are laterally supported in the short direction by concrete shearwalls, while the long direction is supported by special concrete moment frames that terminate at the bases of the towers. The use of moment frames that were nearly the entire length of the floor kept the forces in the beams low and allowed a shallow structure to minimize floor height. Below the third level of the west tower the supporting columns slope, creating a horizontal gravity thrust that needed to be accounted for in the lateral system.

The helistop that connects the east and west towers is supported by eleven, 120-foot-long, 5-foot-deep castellated beams. The castellated beams weigh the same as standard wide-flange beams but are 30 percent to 50 percent stronger and 50 percent deeper, thus adding structural load capacity and stiffness without adding weight.

The connection of the two towers, at both the roof and bridges at Levels 5 and 6, created structural challenges accommodating the differential deflection of the separated elements. To minimize the movement of the towers, which tended toward deflection amplified by torsional effects, the helistop was ultimately used as a diaphragm to control the torsional deflection of the residential towers. This allowed separation joints between elements to be minimized, as well as provided reduced deflection criteria for the sensitive curtainwalls and scrims cladding the towers’ exteriors.

In developing the structural model for the academic form, multiple iterations of geometry refinement were coordinated with the architect’s model. The thickness of the exterior assembly was determined by the factory-assembled panel system, including tolerance and connection details, and the structural shape was set using a 3D shell created by offsetting the architect’s exterior shape. Through close collaboration, both the aesthetic and functional intentions of the architecture were used to aid in shaping the appropriate structural systems and geometry.

Numerous subcontractor models, in addition to the structural, architectural, and mechanical models, were combined for multidiscipline BIM coordination and conflict identification. During construction, 3D models (along with traditional 2D drawings) were submitted by the structural steel contractor to more clearly explain the unique geometry and details required at the academic form. The appropriate use of design and coordination programs contributed to the successful delivery of Emerson College Los Angeles on-time and on-budget.

Projects less than $15 million
American Physical Society, Ridge, N.Y., and Vertical House, Dallas, received National Awards for projects less than $15 million. In late 2014, the American Physical Society renovated its 30,000-square-foot editorial headquarters and added 18,500 square feet above it. The Long Island Pine Barrens Preservation Act prohibited expanding the building’s footprint, hence the addition had to occur above the existing structure.

To meet the project’s $6 million construction budget, operation of the facility could not be interrupted while the work was performed to eliminate leasing of temporary space and employee relocation. The entire construction, including columns, floor, and roof framing, was achieved with the building occupied and in operation.

Structural engineering involvement (structural engineer: Gilsanz Murray Steficek, New York) started in 2009 during dismal economic times. To minimize cost, the steel was purchased and fabricated in advance and stored offsite in a controlled environment before it was required for erection. This strategy proved to be cost-effective even after including the storage cost.

The existing structure — footings, columns, roof framing, and lateral system — did not have the capacity to support the additional second story loads. The design allowed the new steel to be installed without disrupting the building’s ongoing use. The long-span design with a column grid up to 38 feet by 62 feet results in spacious, column-free, and architecturally flexible interiors with minimal penetrations through the existing ground floor.

The majority of the perimeter columns were located outside the walls of the existing building, forming an exoskeleton, and in its existing courtyard. The W12 columns of the new frame are situated 5 feet to 9 feet outside the perimeter of the existing structure, eliminating interference with the existing foundation, and allowed most of the foundation work to be done outside the building. Only six columns penetrate the interior of the old building. These columns and footings were installed one at a time with limited impact to the occupied building.

The new second floor is elevated 4 feet above the existing roof, providing a 4-foot interstitial space that serves both the existing building below and new structure above. The mechanical services then could be distributed efficiently from the rooftop equipment on top of the single-story building. The existing roof served as the working platform for erection of the second-floor framing.

The thermal analysis of the exoskeleton accounts for differential expansion and contraction created by temperature differences between the interior and exterior of the building. All members that penetrate the building envelope are insulated for the first 8 feet as they enter the building. A series of skewed W8x24 members brace the exterior beam-column connections to resist lateral loads and to dissipate the increased stresses caused by the temperature differentials.

The long-span design took into account deflection, vibration, and construction of the steel members. The 57-foot-long W24 filler beams span N-S between W30 and W36 E-W girders, which in turn frame into columns at the interior. At the north side, the girders are offset from the columns, serve as spandrels beams, and are located within the building envelope. These spandrels frame into 62-foot-long W30 beams at the N-S column line that extend through the envelope and connect to the exoskeleton columns.

The building’s lateral system consists of eight braced frames, which utilize diagonal HSS8x8 braces that frame at three locations around the perimeter of the exoskeleton, two locations within the existing single-story section of the structure, and three visually exposed locations at the new double-height interior atrium. The existing one-story building was laterally upgraded by tying it to the new two-story structure so that the building behaves as one.

Floor slabs consist of 2-1/2-inch normal-weight concrete on 3-inch metal deck. To moderate deflection that occurs in long-span frames, the concrete was placed from the center of the diaphragm outward. The design called for slip joints at the top of all interior partition walls so that deflection under snow loads or other live loads would not impose load and cause interior partitions to buckle.

Located on one of the highest sites in Dallas, minutes away from downtown, the Vertical House (structural engineer: Datum Engineers, Austin, Texas) five-story residence rises 58 feet above the surrounding landscape. The compact footprint of the project is sectionally integrated into the site via a carved spiraling entry drive that allows for an almost subterranean experience of the existing natural canopy, while the verticality of the two exterior screen walls accents the home’s slenderness and height.

Visitors to the house arrive at natural grade and then cross over the excavated area via an internally stabilized AESS foot bridge to the front entry. The 4-foot-wide foot bridge is framed with a pair of C15x50 edge stringers, each spanning 43 feet. Vertical and horizontal diaphragm X-rod bracing is provided in panel bays of 4-foot, 3-½-inches, with a steel grating floor accented by thin strips of glass flooring on the edges.

The tight floor-to-floor requirements of the project required a close integration of the various building systems, without compromising, and preserving the structural integrity and architectural expression. The interior elevated floor framing consists of a series of shallow-depth wide-flange beams with shear studs, supporting a 1-½-inch-deep composite metal deck filled with 2-¾-inch concrete above the deck flutes.

Each wide-flange beam is connected via welded moment connections to a stiff C15x50 steel channel along the perimeter walls, which distributes the vertical loads from the conventionally spaced interior beams to the closely spaced exterior screen columns. The steel Hollow Structural Section (HSS) curtain, which provides vertical support for the floors, is set 1-foot, 4-inches clear of the floor edge. This visual break between the floor and supporting screen of columns was critical to the architectural effect.

Each screen column, positioned proud of the exterior walls, is connected to the perimeter channel via a vertical ¾-inch-thick steel plate at each floor level; each plate not only transmits the dead and live loads to the columns, but also provides the required stability bracing against weak axis flexural buckling of each 58-foot-tall screen column via weak axis bending of the cantilevered plate. The stresses in the connection system were relatively small when compared with the nominal capacities, as the structural design of each plate was materially governed by the flexural stiffness requirements for nodal bracing.

The solid volume, clad in locally abundant limestone, is tectonically differentiated from its butt-glazed counterpart with inset windows, providing a pronounced shadow line at penetrations. A glass and AESS “floating stair,” along with an adjacent elevator core, provide the primary vertical circulation of the residence. The AESS stair is comprised of 1-inch by 4-inch steel plate stringers oriented in a “zigzag” geometry that follows the pattern of the AESS tread and riser plates. The stair terminates at a fifth-level open-air roof terrace, which provides 360-degree views of Dallas; the terrace is shaded from the afternoon sun by an extension of the HSS6x2 screen columns, which folds at the roof level to form a horizontal roof trellis. The intermediate stair landings are cleverly suspended via two disguised thin steel rods; each rod hangs from the screen-turned-trellis, creating a “floating stair” aesthetic.

Merit Awards for projects less than $15 million total constructed value were presented to:

The Hillary Rodham Clinton Children’s Library and Learning Center, Little Rock, Ark.
Principal Riverwalk Pavilion, Des Moines, Iowa

Projects $15 million to $75 million
Nu Skin Innovation Center, Provo, Utah, and Rutgers University School of Business, Piscataway, N.J., received National Awards for projects $15 million to $75 million total construction value. The 170,000-square-foot Nu Skin Innovation Center (structural engineer: Magnusson Klemencic Associates, Seattle) houses research laboratories, conference spaces, two cafés, a retail storefront, a fitness center, three floors of executive offices, and a data center in a series of elegant, light-filled spaces. Project cost was $74 million.

The Innovation Center is comprised of three primary elements: a three-story building to the north that responds to the scale of Provo’s historic Center Street; a six-story steel-framed building to the south; and a four-story atrium linking the new buildings to each other and to the existing Nu Skin office tower. The atrium is the heart of the new campus, acting as a glazed spine and entry hall designed to host thousands of people from around the world and to accommodate multiple activities and events concurrently.

Visitors and employees enter the atrium through a transparent, glazed volume between the existing Nu Skin office tower and the new office buildings that visually connects the north and south sides of the campus. Telescoping glass walls open to a 500-seat meeting room and offer views of a new garden and the Nu Skin campus to the south. Across from the meeting room, a grand staircase draws visitors and staff up to the data center, laboratory, and office levels that are connected by circulation paths bridging across the space. Underneath the stair, a cantilevered concrete slab marks the entry to an auditorium space clad in maple wall and ceiling panels. A café at the west end of the space affords views of Center Street, linking the atrium with the outdoors.

Above the atrium, glass conference rooms cantilever into the space and a gently curving ceiling of translucent glass is suspended below steel trusses supporting the sky-lit roof, mitigating the intense Utah sunlight and softening the interior space.

The exterior of the Innovation Center is composed of sleek, transparent volumes anchored by aluminum-clad core spaces. Sunshades along the south elevation of the entry hall and offices shade the interior spaces from direct sunlight while framing views of the nearby Wasatch Mountains. Slender steel columns support a canopy on the south elevation that extends the interior spaces into the landscape, while providing shade and protection during inclement weather. Crowning the south building is an airfoil-shaped mechanical penthouse, a nod to the barrel-vaulted forms of the original Nu Skin tower.

The structural systems of each of the buildings respond to the functions within each space. The gravity framing for the North Building consists of concrete columns supporting a 10-inch-thick concrete slab and wide shallow concrete beams. Concrete was used for this structure to minimize the structural depth and the overall building height, effectively controlling vibration in the laboratory space and allowing architecturally exposed soffits in select locations.

The typical framing is comprised of structural steel columns supporting composite steel beams and composite floor slabs with 3 inches of normal-weight concrete over 3-inch steel deck. To eliminate columns in a large meeting room at the first floor, six tower columns are transferred at the third floor. Those columns are supported by two 67-foot-long built-up steel plate girders spanning in the north-south direction and two 85-foot-long story-deep trusses spanning in the east-west direction.

The sharply curved penthouse roof on the South Building is one of the exterior highlights of the project, and the radii of the roof beams vary from 3 feet, 4 inches to 95 feet. Structural steel was vital to this geometry, as was the heroic transfers over the meeting room. Structural steel also facilitated more flexible structural bays in the office areas and reduced construction time for the taller structure.

The atrium is the heart of the Nu Skin campus, and steel framing was essential to create this dramatic space:

• The glass roof is supported by steel girders that span between the North and South Buildings, along with intermediate steel beams and tension bracing.
• The translucent glass ceiling is hung from delicate trusses, which are in turn suspended from the roof girders.
• The 10-foot, 6-inch-wide feature stair rises 29 feet between Levels 1 and 3, and runs 93 feet continuously along the atrium. The stringers and treads are fabricated with steel channels.
• Bridges spanning the atrium are supported simply by steel beams.
• Conference rooms cantilevering into the atrium are supported by remarkably small beams, post and tension rods.
• The four-story-high glass walls are supported by primary and secondary structural steel.

Seismicity in Provo is quite high, and the atrium roof and bridges are not strong enough to tie the buildings together. Therefore, the North and South Buildings are seismically separated with an expansion joint at the north side of the atrium. Lateral forces for the North and South Buildings are resisted by shear walls, which minimize relative movement between the buildings during seismic events.

While it may be unusual to use different structural systems for buildings on either side of a common atrium, the differences in building functions justifies an uncommon solution. In addition to supporting the needs of the individual building functions, the unique structural solution helped accelerate the construction schedule. Construction proceeded on the concrete North Building while the steel was being fabricated for the South Building.

The 150,000-square-foot Rutgers Business School (structural engineer: WSP, New York) is the gateway to Rutgers University’s Livingston Campus in Piscataway, N.J., as envisioned by the campus master plan. The L-shaped form of the building appears to float 60 feet above Rockefeller Road, becoming the physical gate through which most campus traffic passes. The building is designed in keeping with the goals of the master plan toward a high-density academic development complete with urban facilities, shared amenities, and a walkable campus.

Similarly, this building reflects the ongoing shift in higher education that moves away from a focus on classroom-oriented organization and toward a focus on spaces that support collaboration. The building is conceived as three bands — classroom, office, and public spaces — connected vertically by an atrium and horizontally stitched together by scaled communal spaces ranging from personal nooks to collaboration zones to collective spaces.

The Business School, like every new construction at Rutgers University, is LEED Silver equivalent. The building is powered by solar panels located above the adjacent parking lot. Cooling and heating needs are augmented by neighboring geothermal borefields built below the quad. All stormwater is managed through bioswales and retention ponds onsite. The atrium provides high levels of day-lighting into the building and the mechanical system is optimized for lower energy use. Low-VOC materials and specialized carpet tiles enhance the air quality as well.

Structurally, the building includes twelve, 65-foot-long sloping columns that support the “floating” L-shaped form above. The floating L-shaped feature includes a 92-foot column-free span. To achieve this, 60-inch-deep built-up plate girders were used. These 92-foot-long girders are supported by the 65-foot-long sloping columns.

To ensure there would not be a vibration issue with the floating L-shaped portion of the building, the design team created a finite element model to study human-induced vibrations for this area. The team at WSP Structures performed a time history analysis following AISC Design Guide 11 recommendations. Based on the analysis, it was determined that the human-induced vibrations would be considerably less than the acceptable vibration levels defined by the ISO chart in chapter 2 of Design Guide 11.

Steel members also created other architectural features within the building. Exposed bracing inside the building became an architectural feature. Making sure that the lateral forces induced from wind and seismic events could get to the lateral bracing systems turned out to be a challenge. Because of the open nature of the building, numerous openings in the floor diaphragms were required. The numerous openings and the L-shaped section connecting the two parts of the building required the design team to carefully follow the load paths of the wind- and seismic-induced loads.

Projects greater than $75 million
The National September 11 Memorial Museum Pavilion in New York City (structural engineer: BuroHappold Engineering, New York) received a National Award for projects greater than $75 million. The pavilion acts as an open and transparent entry for visitors to the below-grade museum from the memorial site. The 47,600-square-foot cultural facility orients visitors within the memorial grounds and belies the complexity of the site.

Overcoming the many constraints of a site that is situated in dense urban infrastructure and that has been continually transforming since Sept. 11, 2001, required rigorous coordination of architect, engineer, and other project teams working onsite. Integrated structural systems, both above and below grade, impacted the building’s design as well. The team had to take into consideration support for the museum below and other underground infrastructure when calculating structural loads.

The majority of the pavilion is supported over the PATH train station and tracks, while the remainder sits atop the museum. Analysis of these below-grade structures, the memorial pools, and surrounding infrastructure, in addition to the pavilion’s concrete core, identified limited supports capable of carrying the loads of the pavilion. So, a full-story-tall steel truss extends from the pavilion’s core to effectively cantilever the building over the PATH station hall.

The reinforced concrete core provides lateral stability for the pavilion, however, its location above the PATH tracks and station hall complicated the transfer of lateral forces to the ground. To solve this issue, the pavilion is ringed with steel and reinforced-concrete composite drag beams that transfer the forces to the museum’s shear walls. To construct the pavilion shear walls over the tracks, erection trusses support the full weight of the four-story pavilion concrete walls.

Among the most striking features in the pavilion are two 80-foot-tall artifacts known as the “tridents,” which formed the iconic outer structural support of the World Trade Center towers. The tridents are housed in a full-height steel and glass atrium that also extends one story below grade. The atrium steel support is a complex configuration of HSS — HSS20×8 and 20×12 steel tubes — clad with a uniform rectangular curtainwall system set at an angle. Due to their size, the tridents were installed in 2010, prior to the installation of the atrium steel, and protected as the atrium and remainder of the pavilion were constructed.

Within the atrium, the pavilion’s freestanding grand stairs are over 30 feet tall, and the stair widens as it descends, bringing visitors within close proximity to the tridents. The stair has limited support points, creating the appearance of floating within the space. Careful consideration to performance and vibrational aspects of the HSS stair was required to ensure visitors’ comfort as they descend and potentially pause along this feature.

As plans for the site evolved, the structural design was recalculated and adjusted, a feat advanced by the team’s understanding of the tremendous importance of the pavilion, both as a physical presence within the memorial plaza and as the visitors’ entry to the museum.

Mariposa Land Port of Entry, Nogales, Ariz., received a Merit Award for projects greater than $75 million.

Sculpture/art installation
Built for the San Antonio Botanical Gardens’ human-sized birdhouse competition, The Gourd is built out of 70 plates of 12GA Cor-Ten steel that are wrapped around a robin’s egg blue internal octahedron structure and perforated with more than 1,000 Ball Mason jars. The jars illuminate the interior space while providing a visible connection to the outside world. Each steel plate, unique in shape and size, was fabricated using CNC laser cutting technology and emulates the pattern of a dragonfly wing.

This steel structure is comprised of three main components: the schedule 80 steel pipe legs, the rolled pipe octahedron frame, and the Cor-Ten steel skin.

Fastening at only three points around the base of The Gourd, the schedule 80 steel pipe legs provide the structural connection to the ground, with three concrete spread footings providing the foundation for the legs to rest on. These three spread footings are connected together via underground tension cables and turnbuckles to prevent each footing from splaying in the direction of the angled leg.

The steel octahedron structure is fabricated from rolled arcs of schedule 40 pipe and is fastened at their intersections with custom laser cut and bent steel hubs. The hub detail is a pivotal part of the design as it mediates the connection between the rolled pipe frame, the three schedule 80 steel pipe legs, the tube steel floor, and the steel skin. Each hub is designed around an X-shaped disk with four rounded arms, laser cut out of ½-inch plate steel and then bent inward 15-degrees with a CNC-brake. On the upper end of The Gourd, these disks have a 3-inch extension pipe connecting a round bolt plate for fastening the steel skin. At the lower three connection hubs, the extension pipe is fastened on both sides of the “X” disk and is gusseted with ½-inch plate for additional transfer of lateral loads to the legs. The extension on the exterior of the octahedron connects the frame to the legs, sandwiching the skin plates between two round bolt plates. On the interior of the octahedron, the extension pipe connects to a 1-½-inch threaded stud that provides a bolted connection to the three bent steel “J” plates that float the floor off of the structure.

Bent by hand through the process of assembling each faceted plate together, the steel skin becomes a tensile balloon once fully assembled and can be self-supporting. As each plate flexes inward, the skin self inflates while also providing the tensile support to lift the neck of the bottle gourd into its cantilevered position. Combining the structural support of the skin with the structure of the octahedron, The Gourd can delicately rest on the slope of the site while supporting live loads from occupants as well as additional dead loads from the integrated exterior glass apertures.

Fabricated and assembled in house by the design team, the project provided young designers a firsthand education in material characteristics and craftsmanship, as well as working as part of a production team. The project serves as an exemplar model of high-end digital fabrication and finely honed craft.

For more information about the IDEAS2 awards, visit www.aisc.org/ideas2.