Architects tend to get the credit for their buildings’ contributions to the urban realm, but structural engineers play a key, often-overlooked role in turning vision into reality. Structural engineers have to create clever strategies for shoehorning facilities into tight sites, make expansive column-free areas possible within irregular spaces, give stability to unusual stacked or projecting forms, and design highly efficient solutions that conserve material as well as energy resources.
The following ten projects—all completed over the past five years—incorporate creative structural engineering, including a footbridge that can fold and unfold like a Japanese fan, a headquarters building that touches the ground lightly, and a ballpark that extends partly over an active railway.
1. Cooled Conservatories at Gardens by the Bay
The Singapore government’s National Parks Board created Gardens by the Bay as the centerpiece of a new business and leisure district alongside Marina Bay. Two glass, climate-controlled conservatories, billed as the world’s largest free-spanning glass conservatories, contain exotic plants from around the globe. The conservatories rely on a composite structure comprising a grid shell and an external superstructure of radially arranged arched steel ribs, a combination that allowed the engineers to minimize the size of the steel members, maximizing daylight.
A biomass furnace turns waste clippings from the city-state’s street trees into energy to keep the interiors cool in the tropical climate, helping the conservatories achieve carbon neutrality. To exhaust the nontoxic gases that the furnace produces, the team designed 18 tree-like structures dubbed “supertrees,” which reach heights up to 165 feet (50 m). Located outside the conservatories, these structures serve as chimneys, collect solar energy, and support vertical gardens. The Singapore office of landscape architects Grant Associates, the London-based architecture firm Wilkinson Eyre, the London-based structural engineering firm Atelier One, and the local office of environmental engineering firm Atelier Ten collaborated on the project, which opened in 2012.
2. Halifax Central Library
Halifax, Nova Scotia, Canada
Opened in 2014, the Halifax Central Library consists of four glass rectangular enclosed volumes offset and slightly rotated in relation to each other, like a stack of books. The volumes are aligned and shaped to relate to a nearby diagonal street. The municipality requires new buildings to respect the view plane from the historic Halifax Citadel to the harbor to the east. Although the library’s first four floors would fall under the view plane, the fifth floor would not unless it were configured as a narrow bar. Containing a café and seating area, this bar cantilevers out nearly 30 feet (9 m), pointing toward the citadel.
Working with a concept design by Arup of London, local structural engineering firm SNC-Lavalin used two custom-designed Vierendeel trusses—which are open-web trusses that have vertical members, rigid joints, and no diagonals—to achieve the cantilever as unobtrusively as possible and accommodated the building’s large glass atrium with strategic placement of the cast-in-place concrete stair and elevator cores. Schmidt Hammer Lassen Architects of Aarhus, Denmark, was the design architect and local firm Fowler Bauld & Mitchell Ltd. Architecture & Interiors served as architect and prime consultant.
3. Intesa SanPaolo Tower
In designing a new headquarters tower for Intesa SanPaolo bank, the Paris office of architecture firm Renzo Piano Building Workshop decided to raise the building above the ground plane to allow the adjacent public park to connect to the street. London-based Expedition Engineering and local firm Studio Ossola collaborated on the structural design, which lifts the tower by supporting it with just six steel megacolumns and a reinforced concrete circulation core. This solution was made possible by deep two-way transfer structures in the plant-room level and the rear wall of the suspended 364-seat auditorium that supports the internal columns from the 27 office floors above. A three-level, naturally ventilated public greenhouse tops the building, providing expansive views.
Cantilevered off the south side of the tower, a glazed stairwell connecting the office floors filters sunlight by means of vertical gardens and motorized louvers. The precast concrete office floor slabs contain internal voids that passively cool the building; air flows through the voids at night, driven naturally by the stack effect in the double-skin facades on the east and west elevations. The five-level basement includes sunken gardens and building facilities, 300 parking spaces, and water tanks used by the building’s ground-source heat pump system. The 545-foot-high (166 m) tower was completed in 2014.
4. Krishna P. Singh Center for Nanotechnology
The University of Pennsylvania wanted the new Krishna P. Singh Center for Nanotechnology to enliven an uninviting stretch of land at the northeastern edge of campus by celebrating the cutting-edge science inside. But nanotechnology equipment requires strict isolation from vibration, electromagnetic waves, and ultraviolet light, so the building had to be set back from the street and the elevator cores of nearby structures. New York City–based Weiss/Manfredi configured the facility as an L-shaped structure spiraling upward around a landscaped quad, terminating in a glass-enclosed meeting space called the forum, which cantilevers 68 feet (21 m) over the quad at the street edge.
New York City–based structural engineering firm Severud Associates configured the forum to control potential vibration caused by people using it for lectures, receptions, and even dancing. The most vibration-sensitive equipment is tucked into the basement, but nanofabrication conducted in the first floor’s clean room is visible to the galleria behind a long wall of orange glass. Visitors enter the building through a daylit three-story galleria, where a 60-foot-long (18 m) stair, its wide landings sized to encourage interaction, rises to the second floor. The building was completed in 2013.
5. Merchant Square Footbridge
For Merchant Square, an 11-acre (4.5 ha) mixed-use development in London’s West End, local developer European Land & Property held a design competition in 2012 for a pedestrian bridge that would connect two sides of a canal and serve as a focal point for a public garden square. The bridge would need to open to let boats pass underneath, and land ownership constraints required that the bridge structure be supported mostly on the north bank. Ease of maintenance was another key consideration.
Knight Architects of High Wycombe, Buckinghamshire, England, along with local structural engineering firm AKT II, responded with a bridge that opens and closes like a Japanese fan. Five steel beams rise in sequence each Friday to let vessels pass under. Dividing the bridge into five lightweight “fingers” not only turned it into a moving sculpture but also reduced the load on the hydraulic systems, which are assisted by counterweights. When lowered, the pieces fit together precisely to create a flat, safe walking surface. The footbridge was completed in 2014.
6. National Stadium, Singapore Sports Hub
The Singapore Sports Hub is part of the government’s initiative to promote a healthier and more active society, so it is appropriate that the hub’s National Stadium is itself an active building. The largest free-span dome structure in the world, the stadium has not only a retractable roof but also movable seating tiers and turf modules that allow it to be reconfigured to host a wide variety of sports and cultural events, including football, rugby, and cricket.
The local offices of DP Architects, AECOM, and structural engineering firm Arup collaborated on the design of the hub. Arup designed the roof to be unusually thin, using a third of the weight of steel typical for a dome of this size. The lightweight cladding system is translucent, letting in natural light during the day. The roof closes to shade occupants from the city-state’s tropical heat; when the roof opens, spectators have views of the skyline and waterfront. The cooling system delivers cooled air directly to the 55,000 spectator seats, a more energy-efficient strategy than overhead distribution. Completed in 2014, the hub also includes an aquatic center, an arena, the renovated Singapore Indoor Stadium, retail and office space, and community sports facilities.
7. Roy and Diana Vagelos Education Center
New York, New York
For its new medical and graduate studies facility, Columbia University wanted to eschew the typical low-ceilinged, regimented spaces of medical schools and encourage team-based learning and teaching. In response, lead designer Diller Scofidio + Renfro of New York City, in collaboration with the local office of Gensler as executive architect, created a 14-story glass, concrete, and steel building whose defining element they dubbed the “study cascade.” This asymmetrical network stacks two- and three-story neighborhoods containing social and study spaces, all enclosed in glass to allow for views to the Hudson River and expose the activities within. A vertical staircase runs the height of the building’s south side, linking all these spaces.
The design required a structural system that would provide long, open floor spans with no perimeter columns, minimal structural depth, and plenty of strength to avoid torqueing the all-glass facade. Local firm LERA – Leslie E. Robertson Associates supported the irregular cascade of cantilevered concrete slabs with a pair of inclined composite concrete columns, using single-story walls and ramps to provide additional stiffening for the slabs. The facility opened in 2016.
8. Southwest University Park
El Paso, Texas
When Mountain Star Sports Group of Austin, Texas, purchased the Tucson Padres, the city of El Paso agreed to build a new stadium for the Minor League Baseball team. One downtown site fit the bill because it was easily accessible to visitors, was close to the Union Plaza entertainment district, and would not require displacing existing businesses. The hitch: the site sloped steeply, had an irregular shape, and was less than six acres (2.4 ha)—smaller than any other Minor League Baseball stadium site. In addition, an active, sunken Union Pacific Railroad trainway passed along the southern edge, protected by a large concrete retaining wall.
As prime consultant and design architect, Populous of Kansas City, Missouri, worked with associate architect MNK Architects of El Paso and engineering firm Walter P. Moore of Austin, Texas, to squeeze Southwest University Park onto its site by placing 7,500 seats onto four levels rather than the two or three typical of similar ballparks. Parts of the ballpark cantilever over the trainway, with a structural system crafted to avoid any impact to the 1950s-era retaining wall. The first pitch was thrown in 2014.
9. Tilikum Crossing
Tilikum Crossing is the first new span to cross the Willamette River since 1973. Before creating it, the city of Portland and the Tri-County Metropolitan Transportation District of Oregon engaged in an extensive public process. The community’s input, in tandem with strict requirements for seismic performance and the need to accommodate light rail, placed multiple constraints on the architecture firm, Donald MacDonald Architects of San Francisco, and the structural engineering team, T.Y. Lin International of Olympia, Washington, and HNTB Corporation of Bellevue, Washington.
The bridge had to have shorter-than-usual towers to avoid competing visually with nearby existing bridges. So the engineers made the 1,720-foot-long (525 m) concrete bridge a unique combination of two bridge types: traditional cable-stayed and extradosed. Two lanes of track run down the center of the span, flanked by extra-wide pedestrian/cyclist paths that cantilever around the legs of the two stay-cable towers, leaving a gap that creates an updraft that minimizes the force of the wind. The slope of the cables echoes the angle of the Cascade Range in the distance. The bridge opened in 2015.
10. Wallis Annenberg Center for the Performing Arts Goldsmith Theater
Beverly Hills, California
The city of Beverly Hills purchased a shuttered 1930s post office in 1999 with the ultimate goal of creating a cultural center. With funding from the Annenberg Foundation and other donors, the project was initially to locate the theater in the former post office. Studio Pali Fekete Architects of Culver City, California, proposed instead creating a new, larger structure adjacent with room enough for a 500-seat theater; the historic structure would be renovated to house the entrance lobby, educational and administrative spaces, back-of-house functions, and a 150-seat theater. Sinking the new theater 30 feet (9 m) into the ground allowed the theater to have a full-size fly tower without overshadowing the post office. The tower’s red-orange concrete panels are textured to suggest envelopes.
Structural Focus of Gardena, California, had to design the new Bram Goldsmith Theater’s foundation to avoid affecting and being affected by the adjacent underground parking structure. To keep the heating, ventilation, and cooling system from compromising acoustics inside without placing it on the roof, the team cantilevered multilevel mechanical platforms off the fly tower structure. The performing arts center was completed in 2013.
Ron Nyren is a freelance architecture, urban design, and real estate writer based in the San Francisco Bay area.