Structural Steel Ideas


    Twelve structural steel building projects, chosen from nearly 100 submissions received from architectural, engineering, and construction firms throughout the United States, earned national recognition in the 2015 Innovative Design in Engineering and Architecture with Structural Steel awards program (IDEAS2). Conducted annually by the American Institute of Steel Construction (AISC), the IDEAS2 awards honor excellence in steel-frame building design.

    “The 2015 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.

    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; technical or architectural advances in the use of the steel; and the use of innovative design and construction methods.

    Presidential Award of Excellence in Engineering

    The Presidential Award of Excellence in Engineering was presented to the City University of New York’s John Jay College of Criminal Justice expansion project, a new 625,000-square-foot, $400 million academic building in Midtown Manhattan. The facility consists of a 15-story tower on 11th Avenue and a four-story podium with a garden roof that connects to the college’s existing Haaren Hall on 10th Avenue. Following significant growth in criminal justice interest during the last decade, the new building was planned to double the existing facilities and unify the campus into one city block, creating an academic city within a city.

    The John Jay structural system is distinguished by a grid of rooftop trusses that hang the perimeter of eight floors below, which creates a dramatic column-free cafeteria space on the fifth floor.
    Photo: Jason Stone, LERA

    In response to a shallow Amtrak tunnel that cuts through a corner of the site, the John Jay structural system is distinguished by a grid of rooftop trusses that hang the perimeter of eight floors below. This creates a dramatic column-free cafeteria space on the fifth floor with views of the Hudson River for the full 195-foot width of the building. Leslie E. Robertson Associates (LERA), New York, served as structural engineer on the project.

    Two layers of structure are provided to effectively isolate the building from the train vibration and noise. The main building structure cantilevers over and behind the train tunnel, which is enclosed with a hollow core precast plank ceiling and concrete crash walls. At points of convergence, creative detailing was required to maintain the load path and necessary separation.

    Another challenge was accommodating the almost two-story change in grade between 10th and 11th Avenue. A second main entrance to the building occurs along 59th Street and negotiates this steep slope. To design for this condition, the perimeter columns — in an area that supported heavy loads from the rooftop garden — were eliminated, and the entrance was pulled back to allow room for the steps and ramps. Story-deep trusses were placed inside the walls of the fourth-floor classrooms to efficiently accomplish the 40-foot cantilever out to the tip of a V-shaped tapering canopy.

    The interior architecture also responds to the sloped grade with a series of cascading staircases and escalators that complicated the structure, but allowed for fluid circulation to all parts of the campus. A large skylight supported by architecturally exposed narrow tube sections provides natural light into these main circulation areas and offers views in from the garden roof.

    The 65,000-square-foot roof terrace serves as a new, outdoor gathering place for students and faculty. The planted green roof is landscaped with large grassy zones, full-sized trees, and decked outdoor dining areas.

    Accommodating the necessary two layers of structure around the train tunnel mandated a practical limit to the weight that could be supported. After exploring numerous options, the hanging solution was favored by architect Skidmore, Owings & Merrill LLP (SOM) and the Dormitory Authority of the State of New York, and adopted for numerous reasons, including assistance in achieving the series of distinguishing setbacks that frame the west façade’s main entrance along 11th Avenue. The hanging system was continued around the full perimeter to balance the weight, complete the column-free aesthetic, and take advantage of the thin plate hangers which could fit inside standard partition walls instead of traditional column enclosures. To maintain efficiency, the hanging system was stopped where the structure over the tunnel could accommodate conventionally framed floor weight.

    In coordination with the architect, the fifth floor was chosen for this transition, allowing the column-free floor to align with the podium roof garden. The primary construction challenge involved achieving approximately level floors opening day and a 2-inch stack joint in the curtain wall at the transition floor between the conventionally framed and hung structure. To simplify the steel frame erection, the design accounted for temporary columns at the fifth floor around the tower perimeter, and temporary angles bolted to the plate hangers above the sixth floor, to stiffen these elements during erection. This allowed the construction process to proceed similar to conventional construction and maintain the project schedule. Once the truss assembly was finished, jacks at the temporary columns slowly lowered the building and engaged the trusses. At this point the temporary columns and angles could be removed.

    Calculating the required amount of vertical cambering of the steelwork (or how much to super-elevate the perimeter steel at each of the 26 hanger/column locations to account for the anticipated deflection during construction) was a challenge. Design estimates were based on the assumed construction schedule, estimated construction loads, and realistic modeling of the structural behavior. During construction, continuous surveying verified if the perimeter was behaving as anticipated.

    Once a more accurate schedule and shop drawings were available for the nonstructural elements, a full reanalysis was performed incorporating what was being learned from the surveying. During this reanalysis it was determined that the perimeter would likely not come down as much as originally thought — one reason being the curtain wall was 30 percent lighter than assumed — and field adjustments were made to lower the steel frame prior to starting the truss erection. This adjustment proved effective as the final survey data showed the building followed predictions closely and the final stack joint met the intended thickness.

    While the building did not officially submit to the U.S. Green Building Council for certification, the project specifications were written to conform with many LEED certification requirements. The structural steel was sourced from mills regionally close to New York and produced from more than 90 percent recycled content.

    Projects less than $15 million

    The National Award for projects less than $15 million total constructed value was presented to Denver Union Station, Denver. Denver’s historic Union Station is a Beaux Arts landmark located on the edge of the city’s central business district. SOM was commissioned to expand and transform the station and the surrounding 14 city blocks into a major regional transportation hub.

    SOM structural engineers, working closely with SOM architects, designed the Commuter Rail Train Hall structure, light rail station platform canopies, several additional steel-and-fabric pavilions, a pedestrian bridge, and a variety of other steel-and-fabric canopy structures, all part of the greater Denver Union Station Intermodal Hub, which opened in spring 2014.

    The National Award for projects less than $15 million total constructed value was presented to Denver Union Station, Denver.
    Photo: Ryan Dravitz Photography

    The train hall structure is the focal point of Denver Union Station and was conceived as an efficient and formally expressive means of clear-spanning 180 feet across multiple railway tracks. The structure is a rational response to a series of programmatic requirements and constraints. The result is a steel-and-fabric canopy that rises 70 feet at the head-end platform, descends in a dynamic sweep to 22 feet at the center, and then rises again at the far end over an important pedestrian link across the site between Lower Downtown and the Central Platte Valley.

    The primary structural system consists of 11 steel arch trusses spanning nearly 180 feet from a single large-diameter pin connection atop 18-foot-tall arched column supports. The arch-trusses behave as their name implies: in part like a truss, and in part like an arch. Each truss is stabilized by bracing struts between trusses. In the central region of the train hall, the arch-trusses are replaced by cantilevered trusses. Each truss is supported about 20 feet above the ground by a series of steel “kick stands,” which support vertical loads and horizontal thrust. Each kick stand is rigidly connected to the foundation with heavy anchor bolts. The arch-trusses and cantilevered trusses support a tensioned PTFE fabric.

    The above-ground architectural steel structures for Denver Union Station are all composed primarily of round hollow structural section (HSS) steel tubes supporting PTFE tensioned fabric. The exposed painted structural steel was fully detailed in close collaboration with the architectural team to develop a consistent architectural and structural vocabulary throughout the project. All structural connections were fully designed by the structural engineers. Every structural connection and member is both structural and load-carrying, and also an architecturally expressive element.

    As such, the engineers took great time and care to fully detail all members and connections in the contract drawings in order to fully control the design and evaluate aesthetics prior to the shop drawing phase. This work had the additional benefit of eliminating fabricator connection engineering time and cost. To keep the design within budget, the exposed connections were engineered to use only conventional structural steel fabrication techniques and materials but took great care to shape the connections to be aesthetically minimal and consistent.

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

    • Circuit of the Americas Observation Tower and Austin 360 Amphitheater, Austin, Texas
    • Landscape Evolution Observatory at Biosphere 2, Oracle, Ariz.
    • Minnesota Fallen Firefighters Memorial, St. Paul, Minn.
    • Hilton Columbus Downtown High Street Bridge, Columbus, Ohio
    Projects $15 million to $75 million
    The National Award for projects $15 million to $75 million total constructed value was presented to Florida Polytechnic University Innovation Science and Technology Building.
    Photo: Macbeth Photo

    The National Award for projects $15 million to $75 million total constructed value was presented to Florida Polytechnic University Innovation Science and Technology Building, Lakeland, Fla. Florida Polytechnic University, Florida’s newest university and the only one dedicated to a curriculum of science, technology, engineering, and mathematics, started its new campus building program with the 162,000-square-foot Innovation Science and Technology Building designed by architect Santiago Calatrava. Thornton Tomasetti served as structural engineer for the project. This two-story reinforced concrete structure’s signature element is the 250-foot-long glass atrium shaded by 94 operable louver arms, all of which are supported by structural steel boxed plate assemblies spanning up to 72 feet.

    The box plate assemblies are designed to carry not only the load of the glass atrium but also the extreme loads of the shading system’s operable louver arms, which are as long as 62 feet. The louver arms move during the day to act as sun shades. The arms are attached to a structural steel plate stanchion that is field welded to the structural steel plate box assembly. The load is transferred by the box plate assemblies and network of internal plate stiffeners to the foot assembly and then to a reinforced concrete ring beam.

    The structural steel box assemblies were shop fabricated then most were shipped in two pieces due to length and joined in the center at the job site. The lower portion of the plate assemblies are architecturally exposed structural steel (AESS) and exposed to view from the grand hall below. The AESS element has such a smooth finish that most observers mistake this structural steel for another building material.

    Merit Awards for projects $15 million to $75 million total constructed value were presented to:

    • University of Oregon Hatfield-Dowlin Football Performance Center, Eugene, Ore.
    • Pomona College, Studio Art Hall, Claremont, Calif.
    • Central Arizona College, Maricopa Campus, Maricopa, Ariz.
    Projects greater than $75 million

    National Awards for projects greater than $75 million total constructed value were presented to The Vegas High Roller, Las Vegas; and Anaheim Regional Transportation Intermodal Center, Anaheim, Calif.

    The Vega High Roller is the largest observation wheel ever built at 550 feet high with an approximate cost of $300 million.
    Photo: Arup

    Vegas High Roller — The High Roller, opened in March 2014, is the largest observation wheel ever built at 550 feet high with an approximate cost of $300 million. The Hettema Group was appointed as the concept design and ride architect. Caesars Entertainment (the owner) wanted its observation wheel to “appear to be lightweight, without a lot of structure.” Early collaboration between the client, architect, and Arup, the engineer of record, led to a structural scheme with minimal visual impact, affording passengers a “floating sensation” and sense of space. This was achieved with a single rim element and single cabin support bearing. Previous observation wheels, including the London Eye and Singapore Flyer, had wider truss rims and dual cabin bearings, restricting views from the cabin and making passengers more conscious of the structure supporting them.

    Two particularly challenging design constraints of the established design criteria were:

    • passenger comfort in all but the highest winds to minimize downtime and
    • a 50-year design life.

    To ensure passengers would have a stable ride, Arup carried out a wind time history analysis, modeling the spatial correlation between gusts of different sizes and the lateral stiffness afforded by the pre-load in the cables. As there are no codified acceptance criteria for wind-induced accelerations for observation wheels, the predicted movements of the wheel were simulated on a custom motion platform for the client to experience. Through this intuitive and tangible experience the client was able to choose a level of acceleration that would be acceptable, and could decide how frequently they would be willing to shut down the wheel due to high winds. This was then used to determine the level of added damping required to provide a smooth ride.

    The rotation of the wheel generates cyclical stresses in the structure and thus introduces fatigue degradation. Every structural steel component and connection was assessed for fatigue to ensure its projected life met the 50-year design life. In most instances, checks were done according to code. However, where the geometry was particularly complicated and the stress flow harder to determine, detailed solid finite element analysis was used to determine the stress ranges and a more rigorous “hot-spot” analysis undertaken.

    With regard to the cables, the published fatigue data relates primarily to axial stresses. However, as the wheel rotates, the cables are subjected to bi-axial bending and, therefore, the published data is not directly applicable. A unique analytical approach was developed to assess the cables and the results were validated with accelerated fatigue tests on cable specimens that mimicked the expected bending. Through this process it was determined that to meet the 50-year design life, spherical bearings were required at the cable ends.

    The High Roller truly takes advantage of steel’s unique properties and versatility. The rim tube is rolled from structural steel plate; the locked-coil cables are strong and slender; the hub and spindle have forged steel ends welded to structural steel mid-sections; the bearings are high-performance steel subjected to high contact stresses for their 50-year design life; and the anchor bolts to the foundations provide ductility in case of a larger than the Maximum Credible Earthquake.

    The entire structure is fully exposed and apparent to passengers and passers-by. All of the connections can be seen up close and the bolts and welds are clearly visible from within the cabins. At night, thousands of LEDs wash the steelwork (painted white) with programmable changing colors, creating a multitude of colors and dynamic patterns for celebrating special occasions. This structural exposure influenced the design of many of the connections.

    A structure as large and complex as the High Roller with all its custom components presented the delivery team with significant coordination challenges. Arup worked closely with American Bridge, the general contractor, during development of construction documents to ensure the design progressed down an economically and logistically viable route.

    Many of the tolerances exceeded those typically associated with steel structures and the unusual interfaces required careful management — most notably the interfaces between the static elements (boarding platform and drive equipment) and the moving elements (rim and cabins). To coordinate these interfaces, a detailed 3D Navisworks model was developed. This started with the 3D structural steel model and the subcontractors’ components were imported, including cabins, drive equipment, electrical equipment, lighting, and all their associated nuts, bolts, and brackets.

    The 3D model served two key purposes: 1) Having all the components in one spatial model helped with clash detection; and 2) Having a visual aid for coordination discussions allowed all parties to understand how their components related to the whole.

    Many of the final structural components for the High Roller were physically too large and heavy to transport economically to the site and a key challenge was to separate as far as practical the permanent works into sections that could be shipped and lifted into position.

    Through a detailed analysis of the reference design, American Bridge identified optimal locations for bolted splices to enable shipping, trucking, and lifting operations and then fed these back into the detailed design process of the permanent works undertaken by the structural engineer. This collaborative approach gave a schedule advantage, allowing the temporary and permanent works to be designed in parallel, and led to a more efficient structural design tailored to the contractor’s preferred fabrication and erection methods.

    The Anaheim Regional Transportation Intermodal Center includes a 68,000-square-foot terminal building beneath a soaring exposed steel structure.
    Photo: Thornton Tomasetti Inc.

    Anaheim Regional Transportation Intermodal Center (ARTIC) — The ARTIC, a hub for rail, bus, auto, and bike travel, is also ready for high-speed trains and street cars, the region’s next-generation transportation systems. The program includes a 68,000-square-foot terminal building beneath a soaring exposed steel structure. Rising from a height of approximately 80 feet at its southern end to 115 feet at the main entrance and public plaza, the ARTIC structure is approximately 250 feet long and 184 feet wide. The project included the Intermodal Terminal and the Metrolink/Amtrak concourse pedestrian bridge.

    The intermodal terminal features a tapering vault of crisscrossing parallel arches — a lamella arch-shell hybrid. It spans 184 feet over a three-story, interior terminal building housing retail, ticketing, offices, and other amenities. The special concentrically braced frames of the interior structure provide a stiffened base for the shell arches. The roof’s sculptural form is a high-tech take on the simple lines of old airship hangars and the light-filled grandeur of historic train stations. The thin shell’s curved geometry is optimized so that the amount of bending and deflection experienced under non-uniform environmental and seismic loads is minimized. The diagrid shell design has inherent structural redundancy and provides continuous load paths to transfer both gravity loads and lateral loads to the base.

    The structural design for the roof employs long pieces of 14-inch-diameter, curved, interlocking steel pipes that form the complex yet efficient structure’s diagrid shell. Due to the inherent reliance of the shell’s performance on its form, the structural engineer (Thornton Tomasetti) collaborated closely with the architect (HOK) to define its geometry, and a segment taken from a torus based on a catenary cross-section was selected as the most efficient shape to enclose ARTIC’s large interior volume.

    After exploring multiple grids for the shell, Thornton Tomasetti achieved a solution that met structural requirements for performance and efficiency while also fulfilling HOK’s aesthetic and spatial goals. The design was developed to define the arches as a series of compound curves, which made the steel easier to fabricate.

    The steel shell is clearly visible through the façade, creating a variety of impressive visual effects, particularly when lit at night. The terminal is clad in translucent “Teflon-like” material known as ethylene tetrafluoroethylene (ETFE). ARTIC is the largest single installation structure enclosed with ETFE in North America.

    Because so much of ARTIC’s structure is exposed, aesthetic considerations were nearly as important as technical ones. The structural engineer and architect collaborated to design clean details that enhance, rather than detract from, the building’s dramatic sculptural form.

    The northern and southern end walls are glass structures that curve outward supported by tapering, built-up box section masts. These elements double as structural members, acting like bicycle-wheel spokes to stiffen the edge of the roof shell, which otherwise would deflect wildly at the significant end-discontinuities. The glazing system is highly transparent and hangs from the roof via steel cables, which are laterally supported by horizontal girts formed from rolled steel elements and steel armatures connected to the masts.

    The north end-wall masts also support the cantilevering entrance canopy, which in-turn acts as a horizontal truss to laterally brace the masts. ARTIC’s unique design required constructability considerations from an early stage of the project. Thornton Tomasetti collaborated with the general contractor to develop a sequencing plan that required temporary shoring only at the first arches installed; the rest of the roof was self-supporting during erection.

    Working with the steel fabricator, the structural engineer devised an adjustable backing plate for use in the complete joint penetration (CJP) welds that connect the intersecting steel pipes of the roof shell. The construction sequence made traditional internal ring plates impractical since they would get in the way of infilling arch pieces. An internal ring plate was designed that would telescope back into the pipe to allow placement of the infill sections. The design also included a screw and block to allow for the tolerances of the pipe fabrication while maintaining continuous contact between the plate and the interior pipe surface.

    The terminal’s third level provides access to the new concourse bridge, a 262-foot-long covered pedestrian crossing that spans the existing tracks and provides elevator and stair access to the new rail platforms. The steel-framed bridge is supported by elevator shafts at its southern end, utilizing buckling restrained braces (BRBs) to resist lateral forces. At the northern end, groups of raking steel pipe columns with nested BRBs provide vertical and lateral support.

    Due to liquefiable soils, the terminal is constructed on a mat foundation following ground improvement works using deep dynamic compaction, while the bridge is supported by 10-foot-diameter cast-in-place concrete caisson piles placed between the tracks.

    Despite its visual simplicity, ARTIC was a complex and challenging project. The entire design team relied heavily on integrated BIM for design exploration, analysis, team communication, documentation, and coordination during design and in the field. The integrated model will be used by the owner for ongoing operations and maintenance. BIM’s value to the project was recognized by the American Institute of Archtects’ Technology in Architectural Practice Knowledge Community, which awarded the project its “Stellar Architecture Using BIM” citation earlier this year.

    The transit center is expected to achieve LEED Platinum certification by incorporating initiatives including solar energy and potable water consumption reduction, stormwater runoff, construction, operational waste, air emissions reduction, optimization of climate conditions, and open space areas.

    Information provided by the American Institute of Steel Construction (