A new urban development in Sydney, Australia, will combine an underground library filled with natural light and an aboveground public plaza that is expected to become the focal point of the community. An opening in the plaza will provide light for a small garden that library patrons can enjoy. Courtesy of City of Sydney
A new library design for the City of Sydney creates a subterranean space for books topped with a sunny, accessible public plaza.
March 12, 2013—The City of Sydney, Australia, has very clear plans for how its residents will live, work, and play by 2030. It will be a city that is sustainable, economically thriving, and connected to arts and culture, and its greenhouse gas emissions will be 70 percent lower than in 2006, according to the city’s mayor, Clover Moore, and its chief executive officer, Monica Barone, in a statement on the city’s website. Toward that end, a competition for the design of a new library for the city has recently concluded, and the winning concept features a space infused with natural light that will also be cozy and offer plenty of space for reading, studying, and chatting. The design calls for an expansive space in which the community can come together to celebrate, attend movie screenings, or enjoy the outdoors.
Created by the architects Felicity Stewart and Matthias Hollenstein of Sydney-based Stewart Hollenstein in collaboration with Canberra-based Colin Stewart Architects, the design features a belowground, roughly rectangular library topped by a public plaza that will be able to host arts and cultural festivals. The library and plaza will be located on a 14 ha parcel of land that will form the heart of the Green Square Town Centre urban renewal project, according to Matthias Hollenstein, the director of Stewart Hollenstein, who responded in writing to questions posed by Civil Engineering online.
Over the next two decades, the city plans to spend $A8 billion (U.S.$8.2 billion) developing Green Square, a 278 ha area located 3.5 km from the center of Sydney. It is the largest urban development project under way in the country, according to material provided by the city.
“The [Green Square] project will be home to more than 40,000 new residents,” Hollenstein said. “With the density so high, enormous pressure is put on the available public open space.” Placing the plaza over the library ensures that both indoor and outdoor public gathering areas will be readily available and that sunlight will feature in both. A tramway with grass growing between the rails will operate alongside the plaza, and both the tramway and the plaza itself will be accessible to pedestrians and bicyclists from multiple entry points.
The plaza is expected to become a gathering space for the
community. A tram will operate alongside the plaza, accessible to
pedestrians and bicyclists from multiple entry points. Courtesy
of City of Sydney
To create visual and functional links between the upper plaza and the lower library, the complex “has a series of volumes [that] pop up into the plaza and pop down to reveal the interior of the library,” Hollenstein explained. “These volumes activate the plaza and bring a human scale to it.” A six-story tower that climbs above the plaza will provide a number of spaces in which library patrons and staff members can meet. A circular opening within the plaza will provide both natural light to the library and a small garden that patrons can enjoy. Skylights, together with a large, triangular glazed entry structure, will punctuate the plaza, lighting the library by day and glowing in the plaza at night.
The underground structure will comprise a reinforced-concrete raft slab and walls that will form a box beneath the plaza, according to Andrew Johnson, CPEng, a principal of the Sydney office of the global engineering firm Arup, who acted as a consultant on the design. Johnson wrote in response to questions posed by Civil Engineering online.
According to Johnson, one of the biggest challenges from an engineering perspective was “balancing the overall structure’s mass and performance with the buoyancy from the hydrostatic pressure.” In addition to external waterproofing, an internal cavity that will double as an air supply plenum will be included within the two long sides of the library. A drained subfloor also may be required, Johnson said.
The slab that tops the library and forms the base of the plaza will be partially posttensioned to accommodate the irregular column grid that will be used within the library, Johnson said. Prestressing will be required for the longer-span and open areas of the design, and beams will be needed around the open spaces to provide support and control deflections around such elements as the glazed entry structure, Johnson said.
A six-story tower will climb above the plaza from the underground
volume, providing multiple spaces for library patrons and staff to
meet. One end of the underground structure will boast an open-air
amphitheater. Courtesy of City of Sydney
The geotechnical investigation of the site is still to come, but “experience in the area indicates that the raft slab is likely to be founded on medium-dense saturated sands, and depending on the final design groundwater levels, [the structure] may need some tension piling or ground anchors in some areas,” Johnson explained.
The tower will be have a reinforced-concrete frame, Johnson said. Stability will be provided by concrete shear walls that will envelop the eccentrically located elevator and stairway core, and the floors may also be posttensioned on-site, he said. Precast-concrete systems may be considered in the next design phase for both the library and the tower, Johnson said.
Thermal efficiency and other elements of sustainable design are crucial to the project; the library’s sunken design will take advantage of the thermal constancy of the surrounding earth for insulation and to minimize the amount of heating and cooling needed, according to material provided by the city. A passive ventilation and cooling system and operable windows in the tower will decrease the energy needs of the complex, although a small backup cooling system will be available. The complex is designed so that it can connect to the city’s proposed “green” transformer plant.
“The biggest challenge was to prove that such an unconventional building solution could respond simultaneously to questions about the future of libraries, how you might place a building in a plaza, and how a building could become a piece of social infrastructure,” Hollenstein said. “It had to do all of this while still being sustainable, on budget, and distinctly beautiful.”
The city council endorsed the jury’s decision in the design competition on February 25. The library project is currently budgeted at $A25 million (U.S.$25.6 million), and an additional $A15 million (U.S.$15.3 million) has been allocated for the public plaza. According to material provided by the city, the design is currently being refined, and construction will probably conclude by 2017.